OTHER Self Study Program 861503 – Noise, Vibration and Harshness SSP-861503-Noise-Vibration-and-Harshness

Noise, Vibration,
and Harshness

Self Study Program

Course Number 861503

Volkswagen of America, Inc.
Service Training
Printed in U.S.A.
Printed 03/2005
Course Number 861503

©2005 Volkswagen of America, Inc.

All rights reserved.

Information contained in this manual is based
on the latest information available at the time
of printing and is subject to the copyright
and other intellectual property rights of
Volkswagen of America, Inc., its affiliated
companies and its licensors.

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Volkswagen of America, Inc.

Always check Technical Bulletins and the
Volkswagen Worldwide Repair Information
System for information that may supersede
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respective owners.

Table of Contents

Course Goals ..................................................................................... 1

Introduction ...................................................................................... 2

Theory ................................................................................................ 3

Characteristics of Noise, Vibration and Harshness (NVH), Generation of
Noise and Vibration, Sound and Sound Waves, Audible Range of Sound, NVH
Terminology, Types of Noise, Compelling Force and Vibrating Body, Vibration,
Vibration Transfer Path, Vibration Order, Types of Vibration, Ride Comfort

Diagnosis ......................................................................................... 24

Getting Good Information from Service Advisors, The Four Steps, Diagnosing
and Solving Customer Concerns, Other Information Sources, Pre-Road Test
Inspection, Road Test Tips, Road Testing

Engine Vibrations ............................................................................ 32

Engine Speed-Related Vibrations, Types of Engine Vibrations, Engine Vibration
Formula, Engine Accessory Formula, Types of Engine Noise, Exhaust Noise,
Engine Firing Frequency Formula

Vehicle Speed Vibrations ............................................................... 44

Tires and Wheels, Tire Vibration Formulas, Drive Shaft Frequency Formula,
Drive and Axle Shafts, Driveline Vibration, Transmission Noise and Vibrations,
Differential Operation, Driveline Snap, Suspension Components, Steering
Components

All-Wheel Drive Systems ............................................................... 62

4Motion All-Wheel Drive, 4XMOTION, Haldex Coupling

Tools ................................................................................................. 68

Sirometer, EVA II, ChassisEAR, Hunter's GSP9700 Series, Other Tools

Glossary ........................................................................................... 73

Diagnostic Flow Chart .................................................................... 75

Knowledge Assessment ................................................................. 77

The Self-Study Program provides you with information
regarding designs and functions.

New!

Important/Note!

The Self-Study Program is not a repair manual.

For maintenance and repair work, always refer to the
current technical literature.

i

Course Goals

Course Goals

This course will enable you to:

• Identify the terminology used in diagnosing
Noise, Vibration, and Harshness (NVH)
concerns

• Identify the different types of NVH

• Identify the steps of the NVH systematic
diagnostic approach

• Identify the road test procedures
necessary to isolate a noise or vibration

• Calculate NVH frequencies necessary for
component classification

• Identify test equipment and tools used in
diagnosing and correcting NVH concerns

• Identify, diagnose, and specify the
component causing the NVH concern

1

Introduction

Introduction

This Self-Study Program focuses on vehicle
Noise, Vibration, and Harshness (NVH), their
causes and diagnostic and service procedures
to locate and correct NVH concerns.

Modern cars and trucks use a combination
of systems to provide the driver with the
safest, most responsive, and comfortable
vehicle ever built. Today’s driver has come to
expect a smooth and quiet ride in all operating
environments. When vehicle noise, vibration,
or ride harshness exceeds the driver’s
expectations, it is up to the technician to correct
the cause of the customer’s concern.

Vehicle components are being manufactured
using lighter weight metals. Lighter weight
metals reduce the overall vehicle weight that
reduce emissions and improve fuel economy.
As technologies develop stronger and more
lightweight metals this trend will continue.
Lighter vehicle components do not absorb
noises and vibrations as well as heavier
components. This leads to an increase in NVH
concerns.

Diagnosing NVH concerns has been developed

into a logical and almost scientific procedure.
This course will provide the Volkswagen
technician with concepts to help understand and
diagnose NVH concerns.

2

2

Theory



Characteristics of
Noise, Vibration, Harshness

Noise is defined as any unpleasant or
unexpected sound created by a vibrating object.

Vibration is defined as any objectionable
repetitive motion of an object, back-and-forth or
up-and-down.

Harshness is defined as an aggressive
suspension feel or lack of “give” in response to
a single input.

Generation of Noise and Vibration

A vibrating object normally produces sound, and
that sound may be an annoying noise. In the
case where a vibrating body is the direct source
of noise (such as combustion causing the
engine to vibrate), the vibrating body or source
is easy to find. In other cases, the vibrating body
may generate a small vibration only.

This small vibration may cause a larger vibration
or noise due to the vibrating body’s contact
with other parts. When this happens, attention
focuses on where the large vibration or noise
occurs while the real source often escapes
notice.

An understanding of noise and vibration
generation assists with the troubleshooting
process. The development of a small noise
into a larger noise begins when a vibration
source (compelling force) generates a vibration.
Resonance amplifies the vibration with other
vehicle parts. The vibrating body (sound
generating body) then receives transmission of
the amplified vibration.

3

Theory

90018503

Sounds and Sound Waves

A sound wave’s cycle, period, frequency, and
amplitude determine the physical qualities of the
sound wave. The physical qualities of sound are:

• Audible range of sound

• Pitch

• Intensity

All people have different capabilities for hearing
sound. Some people may not hear sounds
that other people can hear. Keep these facts in
mind while diagnosing noise concerns. Most
customers become tuned into a noise after
hearing it repetitively.

When diagnosing a vehicle, it may
be beneficial to have the customer
reproduce the noise during a road test.

Audible Range of Sound

For sound to be heard, the resulting acoustic
wave must have a range of 20 to 20,000 Hz,
which is the audible range of sound for humans.
While many vehicle noises are capable of being
heard, some NVH noises are not in the audible
range.

Low-speed droning is an example of a low
frequency NVH concern that may have
components not in the audible range. This
condition exerts pressure on the driver’s
eardrum and can be extremely uncomfortable.

On the other end of the audible range of vehicle
noises are wind noise and brake squeaking.
The high frequencies of these NVH concerns
produce a high-pitched noise that can be
extremely annoying. The figure below illustrates
the audible range of automotive noises.

120

100

80

60

40

Minimum Audible Level

20

SOUND LEVEL INTENSITY (dB)

0

Maximum Audible Level

10050 500

FREQUENCY (Hz)

Average Audible Level

1k

5k 10k

4

90018504

TIME

1st Cycle

2nd Cycle

3rd Cycle

90018505

1st Cycle

2nd Cycle

3rd Cycle 4th Cycle 5th Cycle 6th Cycle 7th Cycle

Fre

quency Equals 7 Cycles Per Second or 7 Hz

1 Second

TIME

NVH Terminology

There are common terms used when discussing
an NVH concern. The following terms and
graphics will help when discussing NVH with
other people with a technical background.

Cycle

Theory

Cycle is the path a wave travels before the wave
begins to repeat the path again. If an Alternating
Current (AC) sine wave begins a path at zero
volts, the wave completes one cycle when it
returns to zero volts from a positive voltage.

Frequency

In other words, the wave completes one cycle
by traveling the path from a negative voltage to
zero volts, then to a positive voltage, and then
back to zero volts.

Frequency is the number of complete cycles
that occur in one second. Sound and vibration
waves are measured in Hz, or Cycles Per
Second (CPS). One Hz is equal to one CPS.

The sound wave in the figure below has a
frequency of 7 Hz because it completes seven
CPS. The frequency of a sound or vibration can
aid in troubleshooting an NVH concern.

5

Theory

90018506

AMPLITUDE

Minimum

Maximum

90018501

Pitch

Pitch is the physical quality of sound that relates
to the frequency of the wave. Increasing the
frequency of a sound increases the pitch of
the sound. If frequency decreases, pitch also
decreases.

Maximum

Listening to an accessory drive belt squeaking
is an example of a high pitched, high frequency
type of noise. A high pitched, high frequency
noise is irritating to most people.

A roller bearing that makes noise is an example
of a low pitched, low frequency type of noise.

Amplitude

Amplitude refers to the vertical measurement
between the top and the bottom of a wave.

Two waves can have the same frequency, but
differ in amplitude. Amplitude is the quantity
or amount of energy produced by a vibrating
component.

Amplitude

Pitch

Minimum

High Frequency: High Pitch

AMPLITUDE

6

Low Frequency: Low Pitch

TIME

90018502

Sound Intensity

Sound intensity is the physical quality of sound
that relates to the amount and direction of the
flow of acoustic energy at a given position.
The figure illustrates two sound waves with
the same frequency but different amplitudes
(different intensity levels).

Sound intensity is measured in decibels.
A decibel is a unit for expressing relative
difference in power between acoustic signals.
Sounds greater than 160 decibels are dangerous
to human hearing.

Differences in pitch, the source of each sound,
or the person who hears the sound can create
the perception that two sounds of the same
intensity have different levels of loudness.

Theory

Low Amplitude: Low Intensity

AMPLITUDE

High Amplitude: High Intensity

TIME

7

Theory

5

10

15

20

0

20

40

60

80 100

Resonance

Resonance is the tendency of a system to
respond to a compelling force oscillating at, or
near, the natural frequency of the system. All
objects have natural frequencies and experience
maximum response at the point of resonance.

The natural frequency of a typical automotive
front suspension is in the 10 to 15 Hz range. This
is designed for ride and handling considerations.

As seen in the figure, the suspension’s natural
frequency is the same no matter what the
vehicle speed. As the tire speed increases,
along with the vehicle speed, the disturbance
created by the unbalanced tire increases in
frequency. Eventually, the frequency of the
unbalanced tire intersects with the natural
frequency of the suspension, causing the
suspension to vibrate. This intersection point is
called the resonance.

The amplitude of a vibration is greatest at the
point of resonance. Although the vibration can
be felt above and below the problem speed, it is
most prominent at the point of resonance.

Resonance explains why a tire vibration occurs
at certain vehicle speeds. If the vehicle's
suspension has a natural frequency of 13 Hz,
the suspension will transmit, or resonate the
vibration at speeds in the 13 Hz range. The
vehicle will vibrate at 39 mph, 52 mph and
65 mph because these speeds cause a tire
vibration to resonate through the suspension
into the vehicle.

Hz

Suspension Frequency

Compelling Force

Point of Resonance

Vibration Speed

MPH

8

Types of Noise

Theory

There can be many types of noise concerns on
a vehicle. The classification of noises assists the
technician in troubleshooting and repairing the
customer’s vehicle.

Noise is an unpleasant or unexpected sound
created by a vibrating object. Interpretation plays
a large role in defining noise characteristics.
Terms used to describe noise include:

• Droning

• Beat

• Road noise

• Brake squeal

The frequency of noise vibrations is much higher
than that which can only be felt, often ranging
between 20 and 500 Hz. Certain noises can
be associated with the component systems
of a vehicle such as the engine, driveline, axle,
brakes, or body components.

Noise can be annoying to some people, while
others find it acceptable. Automotive noises
can be audible at certain speeds or under
certain driving conditions. A gear-driven unit,
such as an automotive drive axle, produces a
certain amount of noise. In dealing with these
concerns, it is important to know what a normal
condition is and explain it to the customer in
terms they can understand.

Trying to repair a normal vehicle condition can
be frustrating. Despite good intentions, an
attempted repair can also become a liability if
legal action is initiated.

In other situations, a noise can telegraph
through the body of a vehicle. For example,
a chirping noise may be heard in the area of

the instrument panel when, in fact, it is being
produced by the rear brakes. The sound has
traveled, or telegraphed through the parking
brake cables. Following a systematic approach
when troubleshooting an NVH concern helps to
locate the cause and correct the condition.

9

Theory

90018510.EPS

Droning

The sensation people experience when driving
into a tunnel at high speed, or climbing to a
high altitude, is a feeling of ear discomfort. The
ear drums feel as if they are being forced in
or out due to sudden changes in atmospheric
pressure. An unpleasant droning causes a
similar sensation due to large fluctuations of air
pressure in the car.

A customer may refer to unpleasant droning
noises as humming noises. There are three
types of unpleasant droning:

• Low-speed

• Middle-speed

• High-speed

Unpleasant droning at low and middle-speed
driving is a long duration, low-pitched noise that
is non-directional. It is hard to hear and feels like
pressure in the ears.

Feeling a small amplitude vibration is common
with low and middle-speed droning. Low-speed
droning has a range of up to 30 mph (50 kph)
and has a frequency of 30 to 60 Hz. Middle­speed droning has a range of 30 to 50 mph (50
to 80 kph) with a frequency of 60 to 100 Hz.

Unpleasant droning at high-speed driving is a
long duration, non-directional humming noise
that is uncomfortable to the ears. High-speed
droning has a range of 50 mph (80 kph) and up
with a frequency of 100 to 200 Hz.

The three classifications of droning are speed
and frequency related. A low-speed droning
sound has a lower pitch than a high-speed
droning sound.

The table summarizes the speed and frequency
ranges for the three types of droning.

Speed and Frequency Ranges of Droning

FREQUENCY

RANGE

30 to 60 Hz

60 to 100 Hz

100 to 200 Hz

Low-Speed
Droning

Middle­Speed
Droning

High-Speed
Droning

SPEED RANGE

Up to 30 mph
(50 kph)

30 to 50 mph
(50 to 80 kph)

50 mph
(80 kph and up)

10

Theory

90018511.EPS

Droning can occur when accelerating,
decelerating, or driving at a constant speed, but
most often occurs when accelerating. Droning
usually is apparent at a specific engine rpm or
vehicle speed. For example, the figure illustrates
how the noise level of a vehicle increases
with vehicle speed. As vehicle speed reaches
a certain range (the solid colored areas of the
figure), a large increase in the noise level occurs.

Noise

Level

Change

High

Unpleasant

Droning

The speed or rpm range at which unpleasant
droning occurs is relatively narrow. When
droning occurs at a specific vehicle speed, the
range is generally within 3 mph (5 kph) of that
speed. When droning occurs at a specific engine
rpm, the technician should change vehicle speed
very slowly. Changing vehicle speed quickly will
make it difficult to check the droning because
rpm will pass through the specific range too
quickly.

Droning is usually generated by more than one
component. In most cases, it is necessary to
eliminate all the causes in order to remove the
droning noise. For example, unpleasant droning
can occur when engine and driveline vibrations
are transmitted to the body panels causing them
to resonate. Air cleaner, air intake, and exhaust
noises can combine and cause droning in the
passenger compartment.

Other items that are sometimes responsible for
unpleasant droning include:

Noise
Level

Low

Vehicle Speed High

Generating

Sound

• Bending resonance of exhaust pipes

• Resonance of auxiliary equipment

• Bending resonance of propeller shaft

• Resonance of suspension links

• Transmission of engine vibration

• Transmission of exhaust noise

• Transmission of intake air noise

The bending resonance is a normal occurrence
for straight tubes and pipes, and exhaust
and drive shafts. These components deform
(resonate) at known frequencies. Engineers
design components so that the bending
resonance will not occur during the normal
operation of the vehicle.

11

Theory

90018512

Beat

For beat sounds to develop, there must be
two sound sources. For example, striking a
tuning fork produces a pure tone of a certain
frequency (pitch). If a second tuning fork with
a very different pitch is struck, each tone is
distinguishable from one another. However, if
the pitches of the tuning forks are similar, the
two tones produce a beat sound with a pitch
that occurs in cycles at the difference of the two
frequencies. If the pitches of the two sounds
are the same or only slightly different, they
are indistinguishable and are perceived as one
sound.

The figure illustrates two tuning forks producing
sound waves with troughs and peaks. The two
waves have slightly different frequencies. The
sound level becomes higher when their peaks
occur at the same time. The sound level drops
when a peak of one wave occurs at the same
time as the trough of the other wave. When the
two waves combine, they produce a beat sound
in which loudness changes periodically.

The sensation of a beat sound is most
noticeable when the frequency difference is 1
to 6 Hz. If the two frequencies are closer, their
tones are indistinguishable and are sensed
as the same sound. If the two frequencies
are greater than 6 Hz apart, each tone is
distinguishable from one another.

Beat sounds can result from a combination
of many types of vibrations. Common
combinations that result in beat sounds include:

• Engine and air-conditioning compressor

• Engine and power steering hydraulic
pump or other accessories

• Engine and vibrations of the drive shaft

• Tire non-uniformity

• Tire and drive shaft vibrations

A

B

C

Sound Waves C are the sum of Sound Waves A and B
(The fluctuation in Magnitude is Phasing or Beating)

10 Hz

+

8 Hz

=

12

Road Noise

The sounds that occur while driving on gravel
or roughly paved roads is an example of road
noise. This type of noise is continuous and has
a constant character. Road noise can occur at all
vehicle speeds, or when the vehicle is coasting,
and has a frequency range of 30 to 500 Hz. A
very fine vibration also may be noticeable.

Road roughness and tires are major sources of
noise and vibration that occur during driving.
Since the source of road noise is irregular road
surfaces, different types of tires can influence
the amount of road noise. The impact force from
road surfaces transmits to the tires causing
them to vibrate. This vibration, in turn, transmits
to the suspension and body. The resonance
characteristic of the passenger compartment
amplifies the vibration and generates annoying
road noise.

Theory

13

Theory

Brake Squeal

The most common brake system NVH concern
is brake squeal. Brake squeal is a high-pitched
noise. If brake squeal only appears when the
vehicle is first put into operation, it may be due
to moisture on the brake linings.

Brake squeal also can occur when friction is
created between brake components during
braking. Worn or damaged brake components
can produce a vibration resulting in brake squeal.
This high frequency noise can occur under
different brake pedal pressures, vehicle speeds,
and brake temperatures.

Drum brakes usually emit a lower pitch noise
that gets louder with increased brake pedal
pressure. Disc brake noise is generally a high­pitched squeal that occurs under light pedal
pressure.

The major vibration sources of brake squeal are:

• Worn brake shoes

• Non-uniform thickness of brake disc or
drums

• Excessive runout

• Damage or contamination of friction
surfaces

Because of the complex nature of brakes and
the many different parts found in them, the
best way to correct brake squeal is to follow
service procedures. During brake service,
always thoroughly clean any friction surface
before reassembling the brake. A wide variety
of coating materials used on brake backing
surfaces and the installation of shims and clips
can help eliminate brake squeal NVH concerns.

14

Compelling Force and Vibrating Body

Theory

Vibrations occur when there is a compelling
force (or exciting force) acting upon an object
that causes the body to vibrate. Locating the
compelling force (the source of the vibration)
can assist in eliminating an NVH concern.

The major component groups that produce
compelling forces are:

• Tire and wheel

• Driveline

• Engine and torque converter

Vibration

Vibration is the repetitive motion of an object
(back-and-forth or up-and-down). This motion
is a function of time and is measurable in Hz.
Vibration can be described in many ways, which
include:

• Shake

• Shimmy

• Shudder

Vibrations can be constant or variable, and
occur during a portion of the total operating
speed range. Vibrations usually are caused by
some rotating component or components, or
sometimes by the combustion of the air/fuel
mixture in the individual engine cylinders.

Under normal circumstances, a rotating
component does not produce a noticeable
vibration. However, if the component has
improper weight distribution (imbalance), or is
rotating in an eccentric pattern (out-of-round
or bent), then a noticeable vibration may be
produced. If the characteristics of the vibration
can be measured, the information about
the vibration can be used to match it with
components that are the likely cause.

There are many types of vibration problems on
a vehicle. The classification of vibrations assists
the technician in troubleshooting and repairing
the customer concern.

Vibration Transfer Path

Vibrations travel through a vehicle’s structure
similar to the way radio waves travel through
air. Vibrations are often noticed in a component
far removed from where they are generated.
Transmission of a vibration to other components
is called “telegraphing.” For example, an out­of-balance front tire and wheel assembly may
result in a noticeable steering wheel shake. In
this case, the wheel and tire assembly is the
originator of the vibration, the suspension is the
conductor, and the steering wheel is the reactor.

15

Theory

90018509

Vibration Order

Order is the number of disturbances created
in one revolution of a component. A single
high spot on a tire causes one disturbance per
revolution and is called a first-order disturbance.
If the wheel rotates 10 times per second, there
are 10 disturbances per second. This creates a
first-order disturbance of 10 Hz.

If the tire developed a second high spot, a
second-order disturbance would result. The
wheel rotating 10 times per second produces 20
disturbances per second. This creates a second­order disturbance of 20 Hz. Three high spots
create a third-order disturbance and four high
spots create a fourth order disturbance. Higher
order disturbances continue to progress in this
way.

First-order Vibration

The vibration order can aid the technician while
troubleshooting. For example: a vehicle has an
NVH concern that is producing a vibration at 68
Hz. After calculating drive shaft frequency, it is
determined the drive shaft has a frequency of
34 Hz. The second-order frequency of the drive
shaft is 68 Hz. This matches the frequency of
the NVH concern.

By determining that the NVH concern is a
possible second-order vibration, you would look
at components that could cause a vibration
of this type. Universal joints would be a good
component to check because it is possible
they could produce two disturbances with each
revolution of the drive shaft. A missing drive
shaft weight could be eliminated from the list
of possibilities because this situation would
produce a vibration of the first-order.

Second-order Vibration

16

Vibration Order Examples

Theory

Half-order vibration

Half-order vibration is created when any
component that rotates at half the crankshaft
speed is out-of-balance or has excessive runout.
An example of this is camshaft imbalance.
Balancing the component or correcting the
runout may bring the vibration to an acceptable
level.

First-order vibration

First-order vibration is created when any
component that rotates at crankshaft speed
is out of balance or has excessive runout.
Examples are flywheel or torque converter
imbalance and cylinder-to-cylinder mass
differences. In rare cases, the crankshaft itself
may be imbalanced. Balancing the component
or correcting the runout may bring the vibration
to an acceptable level.

Second-order vibration

Second-order vibration is caused by the up-and­down motion of the pistons. This reversal of
mass and motion creates a natural vibration.

Symptoms of engine imbalance include:

• A low-speed shake felt between 480 and
1,200 Revolutions Per Minute (rpm) that
has a frequency of 8 to 20 Hz

• A roughness sometimes felt and heard
between 1,200 to 3,000 rpm at a
frequency of 20 to 50 Hz

First and second-order engine vibrations usually
are detected during the neutral run-up test.

Third-order vibration

A third-order vibration is caused by any
component that has three heavy spots.

17

Theory

Types of Vibration

Vibrations in a vehicle can be any one of the
following types:

• Shake

• Shimmy

• Brake Vibration/Shudder

Shake

Vibrations at the steering wheel or seat, or an
annoying vibration at the floor, are indicators of
“shake.” Shake generally has a frequency of 10
to 30 Hz. There are two types of shake:

• Vertical (up-and-down)

• Lateral (side-to-side)

Vertical shake is severe vertical vibration of the
body, seats, and steering wheel. A trembling
engine hood or rearview mirror also can be a
vertical shake symptom.

Lateral shake is side-to-side vibration of the
body, seats, and steering wheel. A trembling
vibration in the driver’s waist or hips may be a
symptom of a lateral shake.

The major vibration sources of vertical and
lateral shake are:

• Roughness of road

• Tire imbalance

• Non-uniform tires

• Bent or out-of-round wheels

• Driveline

• Engine

18

Shimmy

Vibration that causes the steering wheel to
oscillate is known as “shimmy.” The body of
the vehicle also may vibrate laterally. Shimmy
generally has a frequency of 5 to 15 Hz. There
are two types of shimmy:

• High-speed shimmy

• Low-speed shimmy

High-speed shimmy occurs when driving on
smooth roads at high speeds. High-speed
shimmy typically has a limited speed range in
which symptoms are noticeable.

Low-speed shimmy occurs when the steering
wheel begins to vibrate as the vehicle is driven
across a bump at low speeds.

Theory

The major vibration sources of high-speed and
low-speed shimmy are:

• Roughness of road

• Tire imbalance

• Non-uniform tires

• Bent or out-of-round wheels

For example, a tire with excessive runout, out­of-balance, or out-of-round may cause high or
low-speed shimmy. This is because the tire fault
generates a vibration at a particular frequency.
When the vibration of the tire reaches the
natural frequency of the vehicle’s front unsprung
components (such as the front axle, tires,
and wheels), they start to vibrate. When the
frequency of the front unsprung components
matches the natural frequency of the steering
system, resonance occurs. This resonance
causes the steering wheel to vibrate heavily in
the turning direction.

19

Theory

Brake Vibration/Shudder

Brake vibration/shudder is transmitted through
the brake hydraulic lines to the suspension
system, steering system, and the brake pedal.
Brake pedal pulsation is generated when
applying a brake with a non-uniform diameter
drum or a disc brake with non-uniform brake
disc thickness.

Brake shudder causes the instrument panel,
steering wheel, and sometimes the entire
body to vibrate vertically and back-and-forth
during braking. It also may result in brake pedal
pulsation related to wheel rotation and can
occur during any braking condition or vehicle
speed. Normally, brake shudder has a peak at 40
to 50 mph (60 to 80 kph) and has a frequency of
5 to 30 Hz.

Certain operating conditions can affect the
cause of these vibrations. These include:

• Extended periods where the vehicle is
not in operation

• Brake disc surface irregularities due to
foreign agents (oil or grease, antifreeze,
etc.)

• Deformation of brake disc or drum due to

poor installation

If the disc rotor has excessive thickness
variation, friction force on the braking surface
varies during brake application. The change in
the braking force generates a vibration at a
certain frequency. This vibration is transmitted to
the suspension, steering, and brake pedal. The
vibration can also transmit to the body, causing
it to resonate.

The root cause of disc brake vibration/shudder
concerns is thickness variation. Thickness
variation can be caused by a rotor that has
lateral runout. Lateral runout can be caused
by improper wheel tightening procedures and
torque values as well as hub runout. As the rotor
wobbles (lateral runout), contact is made with
the brake pads. As sections of the rotor make
contact with the pads, small amounts of metal
wear from the rotor surface. This continues
until enough metal is worn in sections to cause
thickness variation. This is why improper wheel
tightening procedures often take weeks or
months to produce brake vibrations.

The same is true for hub runout. Resurfacing or
replacing rotors when the hub has lateral runout
is usually a short-term repair. Always follow
service information for proper wheel tightening
procedures and torque values. Check the hub
for lateral runout when resurfacing or replacing
rotors for a brake vibration.

20

If the vibration or noise is caused by the brake
system, refer to service manual information
for the vehicle. Procedures to check drums
and rotors for out-of-round, thickness variation
and lateral runout are covered in the service
information.

Overtightening wheel bolts, such as
with an impact wrench, often causes
rotor warpage.
Be sure wheel nuts are correctly
torqued.

Ride Comfort

Ride comfort plays a large part in a customer’s
satisfaction with their vehicle. Avoiding abnormal
vibrations ensures a quality ride comfort level.

Normal vehicle vibrations are a result of road
roughness. During normal operation, the
vehicle experiences vibration between the
sprung components (body and suspension) and
the unsprung components (axles, tires, and
wheels). This is an acceptable condition unless
the sprung or unsprung components become
defective, worn, or damaged.

When unsprung components resonate with
the sprung components, the result is poor ride
comfort. Ride comfort vibrations may cause the
vehicle to roll, pitch, and bounce, which may
cause a customer concern. Poor ride comfort
can be minimized by ensuring suspension and
steering components are not damaged or worn.

Theory

21

Theory

Harshness

Harshness results when the vehicle is unable to
absorb vibrations produced by road conditions.
The causes may be due to deterioration of
vehicle components, damage, or modifi cation
of the original equipment. In most cases,
harshness is related to chassis components.

When diagnosing a harshness concern, pay
close attention to interior noise levels in the
vehicle. Many harshness conditions are due
to a component that is not allowed to move
within its normal travel, or one that has lost its
isolating grommets or bushings. This makes
engine mounts, subframe mounts, bushings and
suspension components prime suspects in the
diagnostic procedure.

Oversized tires, heavy-duty springs and shocks,
or other vehicle modifi cations also must be
considered. Some aftermarket tires, even when
they are the correct size, may produce changes
in the vehicle that will generate owner concerns.

Many customers use the word “harshness” to
describe ride comfort concerns. Harshness has
become a universal term when dealing with
NVH concerns on a vehicle. For the purpose
of this course, harshness is an aggressive
suspension feel or lack of “give” in response
to a single input. It can be associated with an
abrupt thumping noise, as well as an aggressive
feel.

Harshness occurs when a vehicle vibrates from
moving across road joints, projections, stepped
differences, or depressions on paved roads.
Driving on the expressway increases the pitch
of the thumping sound. The impact force from
the road surface causes the tires to vibrate.
The tires transmit the vibration through the
suspension system to the car body. Harshness
has a frequency of 30 to 60 Hz.

22

Vibrations

Vibrations are noticeable at the steering wheel,
seats, and floor. The level and intensity of the
vibration changes with the suspension type and
the bushings used.

Longitudinal impact forces are transmitted to the
lower arms where suspension bushings dampen
the vibration. The dampened vibration then
transmits through the suspension crossmember
and strut insulators to the body.

The rigidity of the bushings and insulators in
the vibration transmission path has a large
influence on harshness. The use of low-rigidity
bushings and insulators to provide greater fore­aft suspension compliance softens the impact
force effectively, but results in less responsive
steering.

Theory

Along with suspension system designs,
tire characteristics influence the amount of
harshness. When tires experience an impact
force from a pavement joint, they deform to
cushion the rest of the vehicle. The tires absorb
the force to some extent and are an important
factor when dealing with harshness. At the
same time, the deformation transmits vibration
to other portions of the tires. This causes the

tires to undergo complicated resilient vibrations.
A tire that can absorb vibrations from impact is
efficient in controlling the problem of harshness.

It is extremely difficult for a tire to absorb
harshness vibrations completely. These
vibrations involve not only tire type, but also
inflation pressure. The technician should always
ensure proper tire inflation pressure when
troubleshooting a harshness concern.

Generally, a soft tire with enveloping
characteristics performs well in preventing
harshness. Radial tires have rigid treads and are
low in enveloping characteristics. They tend to
cause harshness, particularly at 19 to 25 mph
(30 to 40 kph).

23

Diagnosis

Getting Good Information from
Service Advisors

To properly diagnose and repair an NVH
concern, the concern will need to be duplicated
during a road test. The service advisors are
a good source for the symptoms and facts
surrounding the concern. Proper questioning
of the customer will usually provide the
information necessary to duplicate the concern.

If the customer is leaving the vehicle and will
be unavailable for a road test later in the day,
then it is advisable that the service advisor
or technician road test with the customer
beforehand to experience the symptoms and
facts of the NVH concern.

The Four Steps

1. Focus the discussion with the customer on
the symptom description.

2. Ask questions that clarify what, when,
where and how often.

Diagnosing and Solving Customer Concerns

1. Describe the concern.

• List known symptoms

• Avoid opinions or disguised solutions

2. Verify and analyze.

• Try to duplicate the concern

• List possible causes

3. Locate the concern.

• Select the probable causes

• Prioritize tasks

• Identify the concern

4. Repair the concern.

• Determine the specific cause

• Perform the repair

3. Summarize your understanding and get
agreement from the customer. Use open-

ended questions to prompt for specifics.

4. Explain what you will do to proceed and get
acknowledgement from the customer.

5. Conduct a quality check.

• Recheck for proper operation and
reassembly

• Check for cleanliness and appearance

Other Information Sources:

• Volkswagen Electronic Service
Information System (VESIS)

– Technical Bulletins

• Other technicians

• Helpline

• Known good vehicle

• This training manual

• The GSP9700 Vibration Control System
Operation Instructions

24

Diagnosis

Pre-Road Test Inspection

Begin checking the vehicle with a visual
inspection. Be sure to carefully inspect the
tires, unless the NVH concern only occurs at
a standstill. Prior to the road test, inspect the
following:

• Tires:

− Pressure – Inflated to specification

− Wear – Cupping, flat spots, feathering
and shoulder wear

− Tread grooves – Correct depth over
entire surface

− Type – The tire is the proper
application

− Foreign debris – Stones, mud, etc.

• Wheels:

Road Test Tips

Observe the following guidelines when
preparing for the road test:

• Check the customer repair order before
beginning the road test. It is important
to know which specific concern the
customer has with his/her vehicle. This
prevents correcting the wrong concern
and increasing the cost of the repair. If
possible, road test with the customer.

• Don’t be misled by the reported location
of the noise or vibration. The cause
actually may be some distance away.

• Remember that the vibrating body may
generate a small vibration only. This
small vibration in turn may cause a larger
vibration or noise due to the vibrating
body’s contact with other components.

− Not deformed or bent

− Weights – Properly installed/correct
size

− Wheel bolts – Torqued to specification

− Tire bead – Uniform

• Driveline:

− Not damaged or bent

− Properly mounted and supported

− Properly aligned

• Engine:

− Belts and accessories for damage

− Properly aligned

− Mounts

• Exhaust:

− Not damaged or bent

• Conduct the road test on a quiet street
where safely duplicating the noise or
vibration is possible. It must be possible
to operate the vehicle at the speed in
which the condition occurs. It is best
to conduct the road test on a route that
has been previously driven with known
good vehicles. This allows for any road
imperfections; i.e. road surfaces and
joints, from being the source of NVH
concerns.

• Turn off the radio and the blower for the
heater and air conditioner unless the
noise or vibration only occurs with the air
conditioning or radio on.

• Determine which test equipment is
needed for the road test. If utilizing test
equipment during a road test, it is best
practice to have an assistant drive while
the equipment is being monitored and
the results recorded.

− Properly aligned

− Properly mounted and supported

• For cold weather climates, be aware that
snow and ice can be the cause of NVH
concerns.

25

Diagnosis

Road Testing

The following road test procedure assists in
classifying an NVH concern into:

• Engine speed

• Vehicle speed

• Wheel speed

Each of the following procedures helps to
eliminate possible components. Depending
upon the cause of the NVH concern, certain
procedures may or may not be necessary.

• Slow Acceleration Test

• Neutral Coast-Down Speed Test

• Downshift Speed Test

• Torque Converter Test

• Steering Input Test 1

Slow Acceleration Test

The first vehicle check to determine a related
symptom of an NVH concern is the slow
acceleration test. This test is used to identify
the noise or vibration if a road test with the
customer was not possible. The steps of the
slow acceleration test are:

1. Slowly accelerate the vehicle to the speed in
which the problem occurs.

2. Note the vehicle speed and the engine rpm.

3. If possible, determine the frequency of the
noise or vibration.

4. Classify the noise or vibration.

• Steering Input Test 2

• Neutral Run-Up Test

• Engine Loaded Test

• Engine Accessory Test

26

Diagnosis

Neutral Coast-Down Speed Test

The next vehicle check when performing the
road test is the neutral coast-down speed test.
This test divides the possible causes of the
noise or vibration into two categories:

• Vehicle speed-related

• Engine speed-related

• Wheel speed-related

The steps of the neutral coast-down speed test
are:

1. Drive the vehicle at a speed higher than the
speed in which the noise or vibration was
obvious in the slow acceleration test.

2. Place the vehicle in Neutral and coast down
through the speed where the concern
occurs.

3. Classify the NVH concern as either vehicle
speed-related or engine speed-related.

• If the noise or vibration exists, then

the concern is vehicle or wheel speed­related. This eliminates the engine and

torque converter as possible causes

• If the NVH concern did not occur during

the neutral coast-down speed test,
perform a downshift speed test to
confirm the concern as engine speed­related

Downshift Speed Test

This vehicle check helps to confirm the NVH
concern as engine speed-related. The steps of
the downshift speed test are:

1. Stop the vehicle and place the transmission
in a lower gear.

2. Drive the vehicle at the engine rpm in which
the noise or vibration occurs.

• If the noise or vibration exists, then the

concern is engine speed-related. This
eliminates tires, wheels, brakes, and
suspension components

• If necessary, repeat the test using other

gears and Neutral to confirm the results

Torque Converter Test

This vehicle check determines how the torque
converter contributes to an engine speed-related
condition. The steps of the torque converter test
are:

1. Drive the vehicle at the speed in which the
NVH concern exists.

2. Operate the torque converter by taking it
in and out of lock-up by lightly depressing
the brake pedal, while maintaining vehicle
speed.

3. Check for noise when the torque converter is
not locked up.

27

Diagnosis

Steering Input Test 1

The next road test steps are the two steering
input tests. These tests determine if the wheel
bearings and other suspension components are
contributing to a speed-related condition.

The steps of the Steering Input Test 1 are:

1. Drive the vehicle at the speed in which the
NVH concern exists.

2. Make wide sweeping turns in both
directions.

• If the concern goes away or gets worse,

wheel bearings, hubs, Universal Joints
(U-joints), drive axles, constant velocity
joints and tire tread wear may be the
components causing the concern

Steering Input Test 2

Perform the Steering Input Test 2 if the NVH
condition occurs when turning only. The steps of
Steering Input Test 2 are:

1. Drive the vehicle at a speed higher than the
speed at which the noise or vibration occurs.

2. Place the vehicle in Neutral and coast down
through the speed where the NVH concern
is obvious, while making wide sweeping
turns in both directions.

• If the concern exists, check for worn

wheel bearings, suspension bushings,
constant velocity joints and U-joints
(contained in the axles of AWD
applications)

• If the vibration does not occur, stop the

vehicle and engage the transmission/
transaxle. Alternately accelerate and
decelerate through the speed at which
the NVH concern appears, while making
wide sweeping turns in both directions

• If the concern returns, then the cause

is dependent upon engine load. The
probable causes are constant velocity
joints or U-joints (contained in the axles
of AWD applications) and loose or
missing wheel nuts

• If the noise is a “clunking sound,” engine

and transaxle mounts, suspension
bushings and U-joints are probable
causes

28

Neutral Run-Up Test

Diagnosis

Perform the Neutral Run-Up Test if the NVH
concern is engine speed-related. Use the test
as a follow-up to the downshift test or when the
NVH concern occurs at idle. The steps are:

1. Increase the engine rpm while in Park or
Neutral.

2. If necessary, make note of the rpm and
frequency of the NVH concern.

Engine Loaded Test

Perform the Engine Loaded Test if the NVH
concern is engine speed-related. This test may
help reproduce engine speed-related concerns
not evident with the neutral run-up or neutral
coast-down speed tests. The engine loaded
test also identifies noise and vibration sensitive
to engine load or torque. These NVH concerns
often appear during heavy acceleration or when
climbing a hill.

Warning: Block the front and back
wheels or injury to personnel may

result. Do not exceed five seconds
when performing the engine loaded
test or damage to the transmission/
transaxle may result.

The steps of the Engine Loaded Test are:

1. Block the front and back wheels.

2. Apply the parking and service brakes.

3. Put the transmission in Drive while keeping
the brakes applied.

4. Increase the engine rpm to the rpm at which
the NVH concern occurred. If necessary,
make note of the rpm and frequency of the
NVH concern.

5. Return engine to idle.

6. Put the transmission in Reverse while
keeping the brakes applied.

7. Increase the engine rpm to the rpm at which
the NVH concern occurred. If necessary,
make note of the rpm and frequency of the
NVH concern.

Immediately after engine loaded test,
run in neutral for 3 minutes at a slightly
elevated rpm to cool the transmission.

If the concern is definitely engine speed-related,
perform the Engine Accessory Test to narrow
down the possible source of the concern

29

Diagnosis

Engine Accessory Test

Perform the Engine Accessory Test if the NVH
concern is engine speed-related. This test helps
locate faulty belts and accessories that are
causing engine speed-related NVH concerns.

The steps are:

1. Block the front and back wheels.

2. Apply the parking and service brakes.

3. Remove the accessory drive belt(s).

4. Increase engine rpm to the rpm at which the
NVH concern occurred.

• If the vibration occurs, the belts and
accessories are not the source of the
concern

• If the belts and accessories are the
source of the NVH concern, continue to
add or remove specific accessory belts
to locate the concern

Caution: With the accessory belt
removed:

• Do not drive the vehicle

• Do not operate the engine for
extended periods
– Water-cooled alternators can fail
– Engines can overheat

30

Notes

31

Engine Vibrations

Engine Speed-Related Vibrations

During the initial vehicle road test, using the
road test procedure, the vibration causing the
concern will be classified into either engine
speed-related or vehicle speed-related. This
section will be used when the vibration is found
to be engine speed-related.

Engine speed-related vibrations are caused
by a component that is driven by the engine.
These components may be part of the engine
assembly or an engine accessory.

Using the frequency of the vibration and
mathematical formulas, the engine speed­related vibration can be classified into these
categories:

• Engine Components

• Engine Accessories

• Engine Cylinders (Firing Frequency)

Types of Engine Vibrations

Many NVH concerns are related to the engine
systems. The operation of the engine creates
a natural vibration. If any one component is
slightly out-of-balance, the natural vibration of
the engine is compounded. Engine vibration is
generally caused by any of the following:

• First and second-order engine imbalance

• Engine firing frequency

• Engine mounts

• Engine accessories

First and Second-Order Engine Imbalance

A first-order engine imbalance is created when
any component that rotates at crankshaft speed
is out-of-balance or has excessive runout.
Examples are harmonic balancer, flywheel or
torque converter imbalance and cylinder-to­cylinder mass differences. In rare cases, the
crankshaft itself may be imbalanced. Balancing
the component or correcting the runout may
bring the vibration to an acceptable level. First­order engine vibrations can be offset by proper
arrangement of crankshaft counterweights.

32

Second-order engine imbalance is caused by the
up-and-down motion of the pistons. This reversal
of mass and motion creates a natural vibration.

Symptoms of engine imbalance include:

• A low-speed shake felt between 480 and
1,200 rpm that has a frequency of 8 to 20
Hz

• A roughness sometimes felt and heard
between 1,200 to 3,000 rpm at a
frequency of 20 to 50 Hz

First and second-order engine imbalances are
usually detected during the Neutral Run-Up Test.

90018522.EPS

Half-Order Engine Vibration

Engine Vibrations

A half-order vibration is created when any
component that rotates at half the crankshaft
speed is out-of-balance or has excessive runout.
An example of this is camshaft imbalance.
Balancing the component or correcting the
runout may bring the vibration to an acceptable
level.

Torque Converter

Although not actually an engine component, the
torque converter rotates at engine speed and its
vibration frequencies are often the same as the
engine. The torque converter is a fluid coupling
that uses transmission fluid to transfer and
multiply engine torque to the input shaft of an
automatic transmission.

The movement of the fluid between the
impeller, which is connected to the engine, and
the turbine, which connects to the transmission,
can sometimes generate a beat sound. If this
is the case, however, the sound disappears
when the torque converter clutch engages,
mechanically locking the impeller and turbine
together.

Another NVH concern that may be caused by
the torque converter is vibration during clutch
engagement. If the converter clutch does not
apply smoothly, it might result in a jerking or
shaking vibration that can be felt throughout
the vehicle. This vibration disappears when the
clutch finally engages completely.

Torque converter imbalance is also a possibility
when dealing with an engine-dependent NVH
concern. Although rare on new vehicles, this
type of vibration may appear if the torque
converter had been replaced or installed
incorrectly during transmission service. Also,
inspect the flexplate for damage, as this could
cause noise or vibration.

Torque Converter

Converter clutch vibrations also can occur
during downshifts and coasting if the clutch
fails to release correctly. If a converter clutch
malfunction is the suspected cause of an
NVH concern, refer to the appropriate service
publications for transmission diagnostic
procedures.

33

Engine Vibrations

Engine Mounts

The first components that isolate vibration from
the engine to the passenger compartment
are engine mounts. Engine and transmission
mounting consists of a number of relatively
small parts and are sometimes ignored when
troubleshooting. However, these parts are
extremely important in preventing noise and
vibration produced by the engine.

Right Side
Engine Mount

Front Crossmember

Left Side Engine Mount

Left Engine Bracket

Vacuum
Connection

Verify last paragraph

Left Engine
Support

Top
Shield

Mount
Cover

Torque reaction force of the engine acts directly
on the transmission, causing engine mounts to
be subjected to a large force. Therefore, engine
mounts must be rigid to stabilize the engine.
On the other hand, to minimize inherent engine
vibrations and noise during all engine speeds,
the engine mounts also must be soft. Any fault
in the engine mounting system can lead directly
to noise and vibration.

Inspect engine mounts for cracks or damage
to the insulator and the bracket. Grounded, the
engine mounted bracket contacting the frame­mounted bracket, or strained engine mounts
may not isolate engine vibrations.

Engine mounts must be installed correctly.
If the mounts are installed incorrectly or
incorrect parts are used, they cannot absorb
engine vibration. Service information details
the procedure to remove and install the engine
mounting bolts and locator pins.

Several Volkswagen models use Electro­Hydraulic Engine Mount Solenoid Valves.
These valves soften or stiffen the engine
mounts depending upon engine operating
characteristics. The system may be the source
of an engine vibration at idle if not operating
properly. Consult with Volkswagen Service
information for system information.

34

Accessory Vibration

Engine accessories can be a source of engine
vibration. For example, air conditioning
compressors are susceptible to overcharging,
which can result in an NVH condition. Accessory
pulley misalignment or faulty components also
can cause vibrations.

With the advent of serpentine belts, it is no
longer possible to remove belts one at a time
to isolate the source component. Because
the serpentine belt drives all components,
one component may affect another through
resonance. If removing the serpentine belt
eliminates the vibration, reinstall the belt and
operate each component separately. By turning
the air conditioning ON and OFF, or by turning
the steering wheel, some components can be
eliminated or isolated as NVH sources.

Engine Vibrations

When diagnosing accessory vibration, make
sure the source of the vibration is not caused by
the engine or engine firing frequencies. Engine
firing frequencies can cause components to
resonate and vibrate. The vibration amplitude
may increase with the accessories loaded.
The most effective repair may be isolating the
disturbance by interrupting its transfer path

rather than attempting to eliminate the source.

35

Engine Vibrations

Engine Vibration Formula

For purposes of vibration diagnosis, the engine
also includes the torque converter and exhaust
system. When an NVH problem is torque
sensitive, the vibration may appear or disappear
at different vehicle speeds (mph/kph), but is
present at the same engine rpm. For example, if
a vehicle has some vibration at 25 mph (40 kph),
40 mph (64 kph) and 65 mph (104.6 kph), but is
worse at a particular speed, the NVH concern
is probably torque sensitive since the condition
occurs at the same engine rpm but at a different
load.

Use the engine rpm at which the NVH symptom
occurs to determine engine frequency. Calculate
engine frequency as follows:

Divide the engine rpm by 60 (the number of
seconds in a minute).

rp m ÷ 6 0 =

H z ( e n g i n e fr e q u e n c y)

For example, if the corresponding engine rpm of
an NVH problem on a vehicle is 2400 rpm, the
resulting engine frequency is 40 Hz.

2 4 0 0 ÷ 6 0 = 4 0 H z

To get the second and third-order frequency,
multiply the first-order frequency by 2 for
second-order, 3 for third-order, etc.

F i r s t - o r d e r x 2 = S e c o n d - or d e r

F i r s t - o r d e r x 3 = T h i r d - o r de r

Engine vibrations also may have half-order
frequencies; half-order frequencies are
calculated by dividing the first-order by 2.

36

F i r s t - o r d e r ÷ 2 = H a l f - o rd e r

Engine Accessory Formula

Engine Vibrations

Belt-driven engine accessories produce
vibrations at different frequencies than the
engine itself. This is because the drive ratio
created by the different size pulleys causes
them to rotate at different speeds. Determining
engine accessory frequency is comparable to
calculating driveline frequency.

Calculate engine accessory frequency by
performing the following steps:

1. Determine the size ratio between the
accessory pulley and the crankshaft pulley
by dividing the crankshaft pulley diameter
by the accessory pulley diameter.

C r a n k s h a ft p u l l e y d i a m e t e r ÷

Ac c e s s o r y p u l l ey d i a m e te r =

P u l l e y r a t i o

For example, if the diameter of the crankshaft
pulley is 152.4 mm (6 inches) and the accessory
pulley diameter is 50.8 mm (2 inches), divide 6
by 2. The accessory pulley rotates three times
for every crankshaft rotation.

2. Multiply the engine rpm in which the NVH
condition occurs by the pulley ratio.

E n g i n e r p m x Pu l l ey r a t i o =

Ac c e s s o r y r p m

For example, if the engine rpm is 2,400 rpm
(engine speed), multiply 2,400 by 3. The
accessory is rotating at 7,200 rpm

2 4 0 0 x 3 = 7 2 0 0 r p m

3. Divide the accessory rpm by 60 (the number
of seconds in a minute) to obtain the
accessory Hz.

Ac c e s s o r y r p m ÷ 6 0 = Ac c e s s o r y H z

For example, the engine accessory rpm is
7,200, divide 7,200 by 60. The engine accessory
frequency is 120 Hz.

7 2 0 0 ÷ 6 0 = 1 2 0 H z

6 ÷ 2 = 3 Ac c e s s o r y H z

37

Engine Vibrations

90018557

Types of Engine Noises

When engine components deviate from the
precise specifications in which they were
engineered, the engine creates excessive or
intolerable noises.

Reciprocating motion of the pistons and the
rotating motion of other engine components
create inherent noises. Causes of engine noises
include:

• Combustion – Noises are produced when
the air/fuel mixture is ignited

• Friction

• Moving parts and the impact between
reciprocating parts

• Tolerance “slap” – Pistons move up-and­down, and the tolerance between parts is
repeatedly pulled in alternating directions

Abnormal Combustion

Any abnormalities in the combustion process
can lead to audible engine vibrations. Abnormal
combustion can include any of the following:

• Spark knock (pinging)

• Backfiring

Detonation (Pinging)

Pinging is generally distinguished by a high­pitched striking noise generated when the
throttle is fully open or during hard acceleration.
If operation is continued in this state, the
pistons and valves are adversely affected,
resulting in a damaged engine.

Causes of engine spark knock (pinging) include
the following:

• Inadequate fuel

• Incorrect timing

• Carbon deposits in the combustion
chamber

38

Engine Vibrations

Backfiring

One type of backfire, known as pop-back, occurs
when the cylinder is fired before the intake
valve closes. When the intake valve opens, the
air/fuel mixture in the intake manifold is ignited
and burns. This situation is sometimes violent
enough to cause an explosive report within
the manifold. Pop-back can be caused by the
following:

• Excessively lean fuel mixture

• Incorrect valve timing

If the mixture is too lean, flame speed
becomes slower, taking longer to complete
the combustion process. If timing has been
disturbed, a pop-back can occur and possibly the
engine will not start.

Another type of backfire is afterfire. Afterfire is
combustion in the exhaust system producing a
loud report or flames at the tail pipe. Conditions
that can produce afterfire are:

• Driving for periods of time with the
engine braked

• The throttle valve closing rapidly

Afterfire occurs when unburned fuel is released
from the combustion chamber and is reheated
by components in the exhaust system. When
the fuel is reheated past its self-ignition point,
afterfire occurs. In some cases, afterfire
can cause damage to the muffler, catalytic
converter, or other components of the exhaust
system. Main causes of afterfire include:

Exhaust Noise

The exhaust system can be a source of noise.
Exhaust noises include:

• Exhaust gas sounds

• Muffler and pipe

Exhaust gas sounds are further subdivided into
three categories:

• Pulsating

• Air column resonance

• Air stream sounds

Exhaust gases are discharged each time the
exhaust valves open, creating a pulsating sound.
The sound is cyclic and is associated with
engine speed and the number of cylinders. The
sound is relatively low-pitched, consisting mainly
of this basic frequency.

Air-column resonance consists of sounds
produced in exhaust pipes and mufflers. Pipe
length and the cross-sectional area of the pipe
determine the frequency. Air stream sounds can
be produced by high-speed exhaust. An example
of this is turbulence caused by air going through
the muffler, or jet noise when exhaust is
discharged from the tailpipe.

Muffler and exhaust noises can be caused
by exhaust system misalignment, incorrectly
installed or damaged mounting brackets, or
failed hangers. This can cause a variety of
annoying noises that can be located with a
thorough visual inspection.

• Rich fuel mixture

• Incorrect ignition or valve timing

• Faulty ignition components

Any of these sounds in the exhaust system can
be carried, or transmitted, throughout many of
the exhaust system components and into the
passenger compartment.

39

Engine Vibrations

Compelling Force of Exhaust

The compelling force of exhaust exiting each
cylinder creates a pulsation on the exhaust
manifold. The pulsating pressure at the exhaust
manifold produces acoustic energy, which is
transmitted to the exhaust pipe. The pulsating
sound waves traveling through the exhaust pipe
are a source of vibration for the exhaust system.
Exhaust vibrations can become amplified by
resonating with engine firing frequencies and
vibrations caused by the reciprocal motion of
the pistons. The combination of these vibrations
can produce unwanted NVH concerns.

Exhaust Hangers

The combination of engine, exhaust, and
acoustic vibrations within the exhaust system
must be dampened. In order to dampen these
vibrations and prevent them from acting on
the body of the vehicle, exhaust hangers must
be specially designed. Exhaust hangers are
designed to suspend the exhaust pipe from the
body and to prevent transmission of vibration
to the body. Exhaust hangers usually consist of
rigid metal to support the system separated by
rubber to dampen the vibration.

Ideally, hangers should be located for support
at points where they bear the weight of the
exhaust uniformly. They are also located at
points of inherent minimum vibration. The
location and tension of the hanger rubber affects
the passenger compartment noise level.

Main muffler hangers are double vibration
proof. The body side of the mount is installed
with a rubber bracket, and the muffler is then
supported by a hanger.

Exhaust Flap

The Volkswagen R32 has an exhaust flap that is
controlled by the Engine Control Module (ECM).
This flap will open or close depending on either
engine speed or other vehicle conditions. When
diagnosing an exhaust noise or other NVH
concern, be sure this flap is operating correctly
and is not the cause of abnormal noises.

40

Engine Vibrations

Exhaust System Symptoms and Corrections

Exhaust system vibrations, symptoms, and possible corrections are listed in the table.

Exhaust System NVH Concerns

CONDITION

SYMPTOM

CORRECTION

Unpleasant droning Generated when exhaust system

vibration is transmitted through
exhaust pipe hangers, and engine
mounts to the body. Causes body
panels and frames to vibrate.

Outside passenger
compartment radiating
noise

Idling vibration Heavy deformation of exhaust

Noise produced by vibration of
exhaust system pipes, muffler
shell, end plate, separator,
exhaust pipe, or shield plate.
Engine racing can reproduce this
noise.

pipes or flexible tubes (collapsed
flexible tubes) can change
vibration characteristics of the
exhaust system, inducing idling
vibration.

Inspect exhaust pipe hangers
and engine mounts for
damage. Tighten or replace
as necessary.

Identify exhaust
component(s) responsible
for the noise, and check
for looseness, damage,
or interference. Adjust or
replace as necessary.

Replace damaged or
deformed exhaust
component.

41

Engine Vibrations

Engine Firing Frequency

All engines have inherent first-order vibrations.
Engines also have vibrations created by firing
frequency. Firing frequency refers to the force
created by the engine each time a cylinder fires.
The force of the combustion creates one pulse,
and with the cylinders firing in order, a natural
vibration is created. The higher the load an
engine is under, the more prominent the firing
frequency becomes. Vibrations also increase
when the engine has a problem that interferes
with the normal combustion cycle.

Symptoms of firing frequency NVH concerns
include:

• Engine rpm sensitivity

• Torque sensitivity

• Low frequency noise

• Shake or buzz

• Loaded engine

If an NVH concern is firing frequency sensitive,
it may be causing resonance of another
component when a specific rpm is reached.

Firing frequency concerns usually have a
narrow rpm range. To prevent the vibrations
created by firing pulses from becoming an
NVH concern, the vibration must be isolated.
Motor mounts are designed to minimize the
amount of vibrations that reach the passenger
compartment.

42

Engine Firing Frequency Formula

Engine fi ring frequency is a term used to
describe the pulses an engine creates from the
fi ring of the cylinders. Engine fi ring frequency
depends upon how many cylinders an engine
has. The number of times an engine fi res a
cylinder with each crankshaft revolution is equal
to one-half the number of cylinders. A four­cylinder engine fi res two cylinders with each
crankshaft revolution. Two revolutions of the
crankshaft fi res all four cylinders. A six-cylinder
engine fi res three cylinders with each crankshaft
revolution. An eight-cylinder engine fi res four
cylinders for each crankshaft revolution.

Calculate the engine fi ring frequency by
performing the following steps:

Divide the engine rpm at which the vibration
occurs by 60.

Engine Vibrations

rp m ÷ 6 0 = E n gi n e H z

For example,

2 , 4 0 0 rp m ÷ 6 0 = 4 0 H z

Multiply engine frequency by half of the number
of cylinders in the engine. (For a four-stroke

engine.)

E n g i n e H z x H a l f t h e n u m b e r o f

c y l i n d e r s = E n g i n e f i ri n g H z

For example,

4 0 x 3 ( s i x c y l i n d e r e n g i n e ) =

1 2 0 E n g i n e Fi ri n g H z

43

Vehicle Speed Vibrations

Vehicle Speed-Related Vibrations

During the initial vehicle road test, using the
road test procedures, the vibration causing the
concern will be classified into either engine
speed-related or vehicle speed-related. This
section will be used when the vibration is found
to be vehicle speed-related.

Vehicle speed-related vibrations are caused by
a component that is rotating at vehicle speed.
These components may be part of the tire and
wheel assemblies or a drive train component
transmitting power to the wheels. There are
drive train components that rotate at tire and
wheel frequencies, i.e. axle shafts or brake
components. The vibration can be diagnosed to
another component rotating at tire frequencies
by substituting tires and wheels of the same
type from a known good vehicle. These
components will need to be diagnosed after a
tire frequency vibration cannot be corrected by
servicing the tire and wheel assemblies.

Using the frequency of the vibration and
mathematical formulas, the vehicle speed­related vibration can be classified into these
categories:

• Tire and Wheel Assembly

• Drive Train Component

Tires and Wheels

Noise and vibration that occur during driving
have various sources. The major sources are the
following:

• Rough or irregular road surfaces

• Condition of the tires and wheels

Impact force caused by rough and irregular road
surfaces is first transmitted to the tires causing
them to vibrate. This characteristic represents
the close relationship that exists between the
tire and road surface.

Tires, just like the suspension, body, and other
components, are designed to minimize noise
and vibration. However, they wear faster than
other components. This is a contributing factor
to tire and wheel noise and vibration.

Tires and wheels can cause vehicle vibrations
for one or more of the following reasons:

• Imbalance

• Excessive radial force variation

• Excessive radial runout

• Excessive lateral runout

• Improperly mounted wheel on the
vehicle’s hub

44

One or more of the following tire properties can
cause tire noise:

• Natural frequency and vibration transfer
characteristics

• Tread patterns

Vehicle Speed Vibrations

Imbalance

When the tire and wheel assembly are rotating
at normal highway speeds, imbalance conditions
are most likely to be noticed by the driver and
the occupants of the passenger compartment.
The first step in correcting a tire and wheel
vibration is to balance the tire and wheel
assembly. There are two methods for balancing
tire and wheel assemblies. They are:

• Static Balancing

• Dynamic Balancing

Static Balancing

As the word static implies, the tire will be
balanced when at rest. For example, if an
unmoving assembly was centered on a cone
and was balanced, it would be statically
balanced. A “bubble balancer” is designed to
statically balance a tire and wheel assembly.

Static imbalance is where there is one amount
of weight located in the center of the tire and
wheel assembly causing an imbalance. As the
weight rotates, centrifugal forces are created
causing the wheel to lift as the weight reaches
top dead center. This lifting motion causes
the tire and wheel assembly to move “up and
down” creating a bounce to be felt.

The static imbalance condition is evident by a
“jiggle” or up-down movement of the steering
wheel. These vibrations may also be apparent
in the body, with or without steering wheel
shake. A statically imbalanced tire driven for an
extended period may cause “cupping“ in the
tire’s tread, create vibration, and adversely affect
handling. Static balancing alone is a seldom­recommended procedure that balances the
assembly using only a single weight plane.

For example, a single weight is commonly
placed on the inner clip weight position for
cosmetic purposes. This is not a recommended
practice and usually results in an assembly that
is not dynamically balanced. The assembly may
then experience side-to-side imbalance while
in motion, causing a shimmy condition and
objectionable vibration.

45

Vehicle Speed Vibrations

90018527

Dynamic Balancing

Dynamic imbalance is defined where one or
more locations of the tire and wheel assembly
are heavier causing an imbalance force or an
imbalance wobble.

The example shown is a tire and wheel
assembly with two heavy spots of equal
weight which are located 180 degrees across
from each other on opposite sides. As this
assembly rotates, centrifugal forces cause a
large imbalance wobble to be created, but the
imbalance force (as well as the static imbalance)
will be zero. A wheel with this condition will
cause a wobble or shimmy to be felt in the
steering wheel. Excessive dynamic imbalance
of this type creates a shimmy that transfers
through the suspension components to the
occupants of the vehicle, especially at higher
speeds.

Dynamic balancers spin the wheel in order to
measure both the up and down imbalance force
and the wobble or shimmy related imbalance
(side-to-side). Dynamic balancers direct the
operator to place correction weights on the
inside and outside correction locations of the
rim so that both imbalance force and imbalance
wobble will be eliminated.

46

Vehicle Speed Vibrations

Mechanical Unloaded Runout

Runout of a tire and wheel assembly directly
affects the amount of imbalance and radial
force variation and should be corrected first.
The smaller the amount of runout, the less
imbalance and force variation. Radial and lateral
runout can be corrected at the same time. There
are two methods to measure runout of the tire
and wheel assembly:

• On-vehicle

• Off-vehicle

Prior to performing a runout measurement,
ensure that the beads are seated equally around
the circumference of the tire.

On-vehicle measurements require the wheel to
be mounted onto the hub and that the wheel
bearing is in good condition.

Once the on-vehicle runout has been checked,
then on off-vehicle check should be taken.

If there is a large difference between runout
measurements on the vehicle and off the
vehicle, then runout is due to one of the
following:

• Stud circle runout

• Hub flange runout

• Some other mounting condition between
the wheel and the vehicle

When diagnosing a tire and wheel
concern on a vehicle, consult the
service information for correct
specifications.

47

Vehicle Speed Vibrations

Mechanical Unloaded Radial Runout

Radial runout of the tire and wheel assembly
should be started at the tire while mounted
to the vehicle. If the tire radial runout
measurements are within specifications, no
further radial measurements of the assembly
need to be measured.

If the radial runout measurements exceed
specifications while mounted on the vehicle,
perform the measurements off-vehicle. The
tire and wheel assembly radial runout can be
measured off-vehicle when mounted on a
balancing machine.

If the off-vehicle runout exceeds specifications,
radial runout of the stud circle and hub flange
needs to be measured. The wheel-to-hub
mounting should be checked to ensure there are
no faults causing the runout.

If the off-vehicle measurement exceeds
specifications, the radial runout of the wheel
assembly should be taken. If the wheel
assembly exceeds specifications, it will need
to be replaced. If the wheel assembly meets
specifications, the tire is at fault and will need to
be replaced.

Mechanical Unloaded Lateral Runout

Lateral runout of the tire and wheel assembly
should be started at the tire while mounted
to the vehicle. If the tire lateral runout
measurements are within specifications, no
further lateral measurements of the assembly
are needed.

If the lateral runout measurements exceed
specifications while mounted on the vehicle,
perform measurements off-vehicle. The tire and
wheel assembly lateral runout can be measured
off-vehicle when mounted on a balancing
machine.

If the off-vehicle runout exceeds specifications,
lateral runout of the stud circle and hub flange
needs to be measured. The wheel to hub
mounting should be checked to ensure there are
no faults causing the runout.

If the off-vehicle measurement exceeds
specifications, the lateral runout of the wheel
assembly should be taken. If the wheel
assembly exceeds specifications, it will need
to be replaced. If the wheel assembly meets
specifications, the tire is at fault and will need to
be replaced.

48

Vehicle Speed Vibrations

90018528

Radial Force Variation (RFV)

The RFV is an industrial measurement term
describing the tire uniformity under load,
measuring the variation (up and down) of the
load acting on the vehicle spindle. All tires have
some non-uniformity in the sidewall and/or
footprint due to variables in the manufacturing
process.

Tire uniformity measurement values can
be affected by rim width, rim condition and
many diverse tire mounting variables. Unlike
balancing, there is often a small amount of RFV
remaining in the tire and wheel assembly after
assembly and this is generally acceptable.

To understand the effects of radial force variation
on vibration, a model of a tire can be used. The
sidewall and footprint can be understood as a
collection of springs between the rim and the
tire contact patch. If the “springs” are not of
uniform stiffness, a varied force is exerted on
the axle and causes it to move up and down
as the tire rotates and flexes. This movement
creates a vibration in the vehicle unrelated to
balance.

A tire with noticeable RFV will produce a
vibration even though it is perfectly balanced

and is within the radial and lateral runout limits.
Manufacturers attempt to minimize the RFV
during tire and wheel assembly.

The RFV can be measured by a load roller
pressing against a rotating tire and wheel
assembly to evaluate the magnitude of existing
assembly harmonics. The Hunter GSP9700
Series Vibration Control System is one method
of determining and possibly correcting for RFV.

Paint marks or tape strips on the tire
and wheel, or valve stem location
in the wheel vary in purpose.
Manufacturers use these markings
for heavy spot, RFV, runout, inventory
control and similar purposes. Without
specific manufacturer information,
they are of little use to the technician.

49

Vehicle Speed Vibrations

Natural Frequency and Vibration Transfer
Characteristics

When a tire is subjected to a compelling force
at one point, it only vibrates there as long as
the frequency of the compelling force is low
(below 30 Hz). When the frequency is high, the
whole tire starts to vibrate. Similar vibrations are
caused when tires are excited by road surface
irregularities. These vibrations have a large effect
on unwanted harshness and road noise.

The relationship between vibration
transmissibility and excitation frequency is
called the “vibration transfer characteristic.”
This is a measure of a tire’s overall vibration
characteristic. Radial and bias tires have a
natural frequency between 90 and 140 Hz,
respectively. The poor harshness characteristics
of a radial tire are due to high transmission of
vibrations at low natural frequencies of about
90 Hz. On the other hand, the poor road noise
characteristics of a bias tire are due to high
vibration transmissibility at natural frequencies
near 140 Hz.

Tire and wheel NVH concerns are low frequency
(usually around 10 to 20 Hz). Knowing the
natural frequency and vibration transfer

characteristics of different tires can help
determine if an NVH concern is due to the tire
type or if the tire is in need of service because
of a runout or imbalance condition.

Tread Patterns

Tire noise associated with tread patterns has
two causes:

• Repeated deformation of the tread
pattern grooves that occurs as the tire
rolls on the road combined with the
resultant flow of air in the grooves

• Continuous striking of the tread pattern
against the road surface

A smooth tread having no pattern on the surface
is the most silent. The noise levels of the tire
tread increases in the order of:

1. Straight rib with grooves running around the
circumference

2. General purpose rib with the zigzag grooves

Tire noise associated with tread patterns will
change pitches when driven on different road
surfaces. Diagnosing tire noise is accomplished
by driving the vehicle on different types of road
surfaces, i.e. asphalt and concrete. The tire
noise will still be present, however it will sound
different on the different road surfaces. Similar
vehicles with the same type tires will also
exhibit the same noise characteristics.

50

Tire Vibration Formulas

Tire Diameter =

Aspect Ratio x Tire Width

2

2540

+ Wheel Diameter

Tire rps per 5 mph =

20800

5

Tire Diameter

3600

Vehicle Speed Vibrations

To determine if a vehicle speed-related vibration
is being caused by a tire and wheel assembly,
use the tire vibration formulas. Tire and wheel
calculations are performed in 5 mph (8 kph)
increments.

Begin by calculating the number of tire and
wheel rotations in 5 mph (8 kph) increments.
The next step is to calculate the RPS per every
5 mph (8 kph). Then, calculate the vehicle speed
where the vibration occurs in 5 mph (8 kph)
increments and calculate the tire and wheel
assembly Hz rate at the vibration speed.

Tire Revolutions per 5 mph (8 kph) Formula

Use the following formula to determine the RPS
per 5 mph (8 kph).

1. Verify the tire size on the vehicle.

2. Determine tire diameter by using the
following formula:

1. Multiply the tire aspect ratio by the tire
width.

2. Divide the above answer by 2540.

3. Multiply the above answer by 2.

4. Add the above answer to the wheel
diameter.

A n s w e r a b ov e + W h e e l d i a m e t e r

10. 7 6 + 1 5 =

2 5 . 7 6 ” ( 6 5 4 . 3 m m ) T i re d i a m e te r

3. Determine RPS in 5 mph (8 kph) increments
using the following formula:

1. Divide 20800 by the tire diameter.

2. Multiply the above answer by 5.

3. Divide the above answer by 3600.

Example: P195/70R15

2 0 8 0 0 ÷ Ti re d i a m e te r

2 0 8 0 0 ÷ 2 5 . 76 = 8 0 7.4 5

A n s w e r a b ov e x 5

8 0 7. 4 5 x 5 = 4 0 3 7.2 5

A n s w e r a b ov e ÷ 3 6 0 0

4 0 3 7.2 5 ÷ 3 6 0 0 =

1. 1 2 R P S a t 5 m p h ( 8 k p h )

Example: P195/70R15

A s p e c t r a t i o x Ti re w i d t h

7 0 x 19 5 = 1 3 6 5 0

A n s w e r a b ov e ÷ 2 5 4 0

1 3 6 5 0 ÷ 2 5 4 0 = 5 . 3 8

A n s w e r a b ov e x 2

5 . 3 8 x 2 = 10. 7 6

This formula has determined that a P195/70R15
tire revolves 1.12 times per second for every 5
mph (8 kph) increment. Using the 1.12 RPS per
5 mph (8 kph), the Hz rate of the tire and wheel
assembly at a given vehicle speed can now be
determined. Use the Tire and Wheel HZ Formula
to calculate the Hz rate at a given vehicle speed.

51

Vehicle Speed Vibrations

Tire and Wheel Hz Formula

Use the tire and wheel Hz formula to calculate a
tire and wheel Hz rate at a given vehicle speed.

Remember, all tire and wheel calculations are
determined in 5 mph (8 kph) increments.

Begin to calculate tire and wheel frequency in
5 mph (8 kph) increments by performing the
following steps:

1. Divide vehicle speed mph by 5 (kph by 8).

This step is necessary due to all calculations

being done in 5 mph (8 kph) increments.

Ve h i cl e s p e e d ÷ 5 =

5 m p h i n c re m e n t

For example, if the corresponding speed of

an NVH problem on a vehicle is 45 mph (72.4
kph), the resulting 5 mph (8 kph) increment
is nine.

4 5 ÷ 5 =

9 ( 5 m p h i n cr e m e n t s )

2. Use the Tire Revolutions at 5 MPH (8 KPH)

Formula (previous page) to determine the tire
and wheel RPS per 5 mph (8 kph).

Example from previous page: If the tire size

on the vehicle is P195/70R15, then the RPS
per 5 mph (8 kph) is 1.12.

3. Multiply the vehicle 5 mph (8 kph) increment
by the tire and wheel RPS per 5 mph (8 kph).

This determines how many times the tire

and wheel assembly revolves per second
at the vehicle speed where the vibration
occurs.

5 m p h i n c re m e n t x Ti r e R P S /5 m p h

=

ti r e a nd w h ee l RP S a t v ib rat io n s pe ed

Example: P195/70R15 at 45 mph

9 x 1. 1 2 =

10. 0 8 R P S a t 4 5 m p h

The tire and wheel assembly revolves 10.08
times per second (or 10 Hz )at the vehicle
speed of 45 mph (72.4 kph).

The calculated frequency of 10 Hz is the first­order tire and wheel frequency.

The second-order frequency of the tire and
wheel assemblies is twice this number, or 20
Hz.

10 x 2 = 2 0 H z

52

The third-order frequency is three times this
number, or 33 Hz.

10 x 3 = 3 0 H z

Drive Shaft Frequency Formula

Vehicle Speed Vibrations

Knowing the tire and wheel frequency allows
for easy calculation of drive shaft frequency. The
drive shaft drives the tires through the rear axle.
Therefore, to determine drive shaft frequency,
multiply tire and wheel frequency by the ratio
of the ring and pinion. Calculate drive shaft
frequency by performing the following steps:

1. Obtain the axle ratio

2. Multiply the tire and wheel frequency at
vibration speed by the axle ratio

T i r e H z x A x l e r a t i o =

D r i v e s h a f t f re q u e n c y

For example, a P195/70R15 equipped vehicle
with a vibration at 45 mph (72.4 kph) and an axle
ratio of 3.90:1.

Using this information, multiply 10 Hz (the tire
and wheel frequency at 5 mph, calculated by
using the Tire and Wheel Frequency Formula) by
the axle ratio of 3.90.

This results in a drive shaft frequency of 39 Hz
at the vehicle speed of 45 mph (72.4 kph).

The calculated frequency of 39 Hz is the first­order drive shaft frequency.

The second-order frequency of the drive shaft is
twice this number, or 78 Hz.

3 5 x 2 = 7 8

It is important to remember the
difference between drive shaft and
axle shaft frequencies. The frequency
of drive shaft concerns are high since
they rotate approximately three to
four times that of the tire and wheel
assemblies. Axle shaft concerns are
lower frequency because they rotate
at tire and wheel speed.

10 x 3 . 9 = 3 9 H z

53

Vehicle Speed Vibrations

Drive Shafts

The function of a drive shaft is to transmit power
from one point to another in a smooth action.
The shafts are designed to send torque through
an angle from the transmission (transfer case on
AWD vehicles), to the axle.

Use exact replacement parts for
attaching the drive shafts. This
ensures safe operation. The specified
torque always must be applied when
tightening the fasteners. Often,
Volkswagen vehicles will have special
procedures to align the engine and
transmission in the vehicle. There are
special procedures to align the drive
shafts as well.

Drive shaft vibrations can be classified into
three different orders: first-order, second-order,
and fourth-order. A first-order vibration may be
caused by a bent or out-of-balance drive shaft
condition. A second-order vibration may be
caused by drive shaft angle, U-joint cancellation,
and worn CV-joints or U-joints. A fourth-order
vibration may be caused by a worn CV-joint or

U-joint.

Driveline Vibration

Driveline vibrations can be caused by:

• Damaged drive shafts

• Missing shaft balance weights

• Worn or out-of-balance wheels

• Loose wheel bolts

• Worn U-joints or constant velocity joints

• Loose or broken springs

• Loose pinion gear nut

• Excessive pinion yoke runout

In addition, check for loose or damaged front­end components or engine/transmission
mounts. These components can contribute to
what appears to be a rear-end vibration. Do
not overlook engine accessories, brackets, and
drive belts. All driveline components should be
examined before attempting any repair.

54

Bent Drive Shafts

A bent drive shaft can cause a vibration
in the vehicle. If a bent drive shaft is
suspected, perform a runout check on the
drive shaft. The dial indicator must be placed
at a 90 degree angle from the drive shaft
for accurate readings. First, measure the
runout close to each yoke weld and verify
it is within the specifications in the service
information. The second measurement is
done in the center of the drive shaft to verify
it is within specifications. If the runout is
not within the specifications, the drive shaft
must be replaced.

Vehicle Speed Vibrations

Front Drive Shafts

Rear Drive Shafts

55

Vehicle Speed Vibrations

90018569

Transmission Noise and Vibrations

Transmission related concerns can cause noise
or vibrations. The purpose of the transmission
is to provide several different gear ranges
to improve vehicle torque and acceleration
qualities. The different gear ranges rotate at
different speeds from the tire and wheel and
shafts.

If the transmission is causing the noise and
vibration it will usually change characteristics
when the different gear ranges are selected.
Most transmission noises and vibration will not
be present when the transmission is placed in
neutral during the road test.

Manual transmissions utilize a clutch assembly
between the engine and transmission. The
clutch assembly can cause noise and vibration.
If it is suspected that the manual transmission
is causing noise and vibration, refer to the
transmission section of the service information
for diagnostic procedures.

Automatic transmissions utilize a torque
converter between the engine and transmission.
The torque converter is driven at engine speed.
Torque converter frequency will match engine

frequency.

A locking torque converter improves fuel
mileage and reduces engine emissions. This
component can cause noise and vibration
concerns. The torque converter operation can
be monitored with a scan tool. Refer to service
information to diagnose torque converter
concerns.

56

Differential Operation

Vehicle Speed Vibrations

The differential gear system divides the torque
between the axle shafts. It allows the axle
shafts to rotate at different speeds when turning
corners. Most differentials consist of a pair
of side gears and a pair of pinion gears. Each
differential side gear is splined to an output
shaft. The pinion gears are mounted on a pinion
shaft and are free to rotate on the shaft. The
pinion gear is fitted in a bore in the differential
case and is positioned at a right angle to the
axle shafts.

In operation, power flow occurs as follows:

• The pinion gear rotates the ring gear

• The ring gear (bolted to the differential
case) rotates the case

• In straight ahead driving, the differential
case rotates as one complete unit, no
differential gears (pinion or side gears)
rotate, and transmit power to the output
shafts

• When cornering, the differential pinion
gears (mounted on the pinion shaft in the

case) rotate the side gears at a difference
in speed allowing the tires to rotate
smoothly

• The side gears (splined to the output
shafts) rotate the shafts, during straight­ahead driving or cornering

Straight-Ahead Driving

During straight-ahead driving, the differential
pinion gears do not rotate on the differential
pinion shaft, because input torque applied to the
gears is divided and distributed equally between
the two side gears. As a result, the pinion gears
revolve with the differential pinion shaft, but do
not rotate around it.

Turning Corners

The outside wheel must travel a greater
distance than the inside wheel in order to
complete a turn. The difference must be
compensated for to prevent the tires from
scuffing and skidding through turns.

The differential allows the axle shafts to turn
at unequal speeds. In this instance, the input
torque applied to the pinion gears is not divided
equally. The pinion gears now rotate around the
pinion mate shaft in opposite directions. This
allows the side gear and axle shaft attached to
the outside wheel to rotate at a faster speed.

If a noise or vibration is being caused by the
differential, the concern will usually change
characteristics during straight-ahead driving and
when turning corners. This is due to the different
operation of the differential when turning.
Differential noises are often torque sensitive
resulting in characteristic changes when
changing torque input.

During a road test, drive in a figure 8 pattern, in
a safe and open area, and determine if the NVH
concern is more pronounced while loading the
differential gears.

Consult the axle section of service information if
it is suspected the differential is causing a noise
or vibration concern.

57

Vehicle Speed Vibrations

Bearing Noise

Wheel bearings and pinion and differential gear
bearings can produce noise when worn or
damaged. Bearing noise can be either a whining
or a growling sound.

Faulty wheel bearings produce noise that
generally changes when the bearings are
loaded. When road testing the vehicle, turn the
vehicle sharply to the left and right. This loads
the bearings and changes the noise level. When
wheel bearing damage is slight, the noise is
usually not noticeable at speeds above 30 mph
(48 kph).

Pinion bearings usually change noise
characteristics when torque input is changed,
i.e. coasting or hard accelerations

Gear Noise

Gear noise usually occurs at specific speed
ranges, usually between 30 and 40 mph (48 and
64 kph) or above 50 mph (80.5 kph). Gear noise
can also occur during specific driving conditions
such as acceleration, deceleration, coast, or
constant load. Gear noises usually disappear
if the vehicle is allowed to coast without any
acceleration or deceleration torque applied to
the gears.

Driveline Snap

A snap or clunk noise when the vehicle is
shifted into gear (or the clutch is engaged) can
be caused by:

• High engine idle speed

• Loose engine/transmission/transfer case
mounts

Axle Shaft

Wheel Bearing

• Worn U-joints

• Loose axle mounts

• Loose pinion gear nut and yoke

• Excessive ring gear backlash

• Excessive side gear/case clearance

The source of a snap or clunking noise can be
determined by raising the vehicle on a hoist
with the wheels free to rotate. Have another
technician shift the transmission into gear
and listen for the noise. A stethoscope, either
manual or electronic, is helpful in isolating the
source of the noise.

Use caution when working around
rotating components.

58

90016434.EPS

Suspension Components

Vehicle Speed Vibrations

The suspension system plays a large role in
the effects of NVH on a vehicle. Similar to the
steering system components, the suspension of
a vehicle can easily act as the medium through
which vibration can be transferred. When the
source of an NVH concern is determined, you
usually can find the cause by performing a
thorough visual inspection.

Passengers of a vehicle are sensitive to the
effects of a harsh riding suspension. For this
reason, various measures are taken in the
design and development phase of a vehicle’s
suspension. For example, springs and bushings
are carefully selected to provide a smooth ride
and also to reduce the impact of steering forces.

The vibration of a vehicle’s suspension system
consists of vertical and longitudinal forces.
The vertical forces are controlled by well­proportioned sprung and unsprung weights,
shocks, and coil springs.

Bushings are designed so they are softer in one
area than in another. Bushings are made softer
in the longitudinal direction so the effects of tire
impact, or road shock, are reduced. Bushings
are made stiffer in the lateral direction so
steering the vehicle does not have as much of
an adverse effect. It is important that bushings
and insulators are in good condition, and they
are of the specified type in order to avoid NVH
concerns in the suspension.

Noise from the suspension is typically caused
by one of the following:

• Loose components

• Worn bushings

• Poor lubrication

Longitudinal forces are controlled by careful
selection of suspension bushings. The
suspension of a particular vehicle is designed so
that the lower control arms absorb longitudinal
impacts from the tires. Tire impact is further

dampened by bushings before being transmitted
through the crossmember to the body. This
longitudinal compliance depends on the spring
constant rate of the rubber insulator bushings.

59

Vehicle Speed Vibrations

Steering Components

Many customer concerns regarding NVH are
related to the steering system. This is because
the driver is holding the steering wheel at all
times while driving, and any vibrations from
the tires or suspension are transferred to the
steering components. Noise-related concerns
are usually generated within the steering
system itself. Vibration-related concerns can be
caused by many different components, including
components in the suspension, tires, and
wheels.

Noise

Some steering system sounds are normal
and should not be of concern. There are some
inherent noises in all power steering systems.
However, other sounds may indicate a problem
within the steering system. Many normal
steering system sounds are related to the
power steering pump. Hissing and rattling are
two steering system related noises that may
occur.

Hiss

A hissing noise usually originates in the steering
gearbox and power steering pump. With the
vehicle stationary, a hissing sound may be
heard when the steering wheel is turned, which
results from fluid pressure pulsation in the
pump.

When diagnosing a hissing noise concern, first
inspect all steering hoses to ensure they are not
touching other parts of the vehicle.

Check service information and technical service
bulletins for possible updated hoses or hose
routings when diagnosing a hissing concern.

Rattle

Rattle usually originates in the steering gear. The
possible causes for this condition are:

• Worn steering or suspension
components

• Worn or damaged rack-and-pinion
retainers and bushings

• Pressure hoses touching other vehicle
components

60

Notes

61

All-Wheel Drive Systems

Because all-wheel drive vehicles have
more moving parts than their 2-wheel drive
counterparts, there is more opportunity for
vibrations to occur. Knowing the construction
and operation of these systems can help in
diagnosis of NVH concerns.

The next few pages contain excerpts from
several SSPs. Refer to the original SSP for more
information.

Refer to SSP 822203, The Passat W8,
for more information.

62

All-Wheel Drive Systems

4Motion All-Wheel Drive

The 4Motion all-wheel drive system is designed
to distribute the drive forces between the front
and rear axles to maintain positive engagement
at the wheels with traction.

The Torsen® differential detects wheel slip in
one axle and distributes the drive power to the
wheels of an axle with better wheel grip.

The Torsen® differential permits limited
differences in speed between the front and
rear axles to allow for ABS control processes. It
operates automatically and reacts independently
of driver input.

The Torsen Differential

Front Axle Worm Gear

Front Axle Drive

Differential Case

Rear Axle Drive

Rear Axle Worm Gear

Spur Gears

Worm Gears

63

All-Wheel Drive Systems

4XMOTION

The power of the Touareg engine is transmitted
to the wheels via the full-time 4 wheel drive,
4XMOTION system.

Transfer Case with
Center Differential,
Differential Lock, and
Reduction Planetary
Gear Set

The front axle differential is a separate
component from the engine/transmission
assembly and is flexibly mounted to the
sub-frame. In addition to being acoustically
beneficial, this also makes it possible to mount
the front wheels further forward.

Front Axle Differential

Rear Axle Differential with
Optional Differential Lock

Refer to SSP 89H303, The Touareg
Suspension and 4XMOTION Systems,
for more information.

64

There are two drive equipment options for the

   

   



 





 

 













4XMOTION system. The open rear differential
is standard equipment while a locking rear
differential is available as an option.

All-Wheel Drive Systems

Open Rear Differential

Optional Locking Rear Differential

M – Motor

AT – Automatic Transmission

TC – Transfer Case

CD – Center Differential

RD – Rear Axle Differential

FD – Front Axle Differential

DL – Differential Lock

EDL – Electronic Differential Lock

The adjustable multi-plate clutch of the center
differential is automatically controlled by the
Differential Control Module J646.

Torque is distributed from the engine to
the front and rear axles via the automatic
transmission and transfer case.

During normal operation, torque is divided
equally between the front and rear axles.

The multi-plate center differential is allowed to
disengage whenever the Differential Control
Module determines a power differential
between the front and rear axles is required, for
example, during cornering.

The driving force between the wheels of
an individual axle is distributed through the
operation of the Electronic Differential Lock
function of the ABS.

The driver also has the option of locking the
center differential (and optional rear differential)
by using a rotary switch in the center console.

Locking the center differential with the switch
overrides automatic control and forces the front
and rear axles to operate at the same speed.

65

All-Wheel Drive Systems

Haldex Coupling

The development of the Haldex coupling is a
giant step forward in modern all-wheel drive
technology. This coupling is controllable, based
on the inputs the Haldex control module
receives from the vehicle.

Slip is no longer the only decisive factor in the
distribution of drive forces — the car’s dynamic
state is also a factor. The Haldex control module
monitors the ABS wheel speed sensors and the
engine control module (accelerator pedal signal)
via the CAN-bus. This data provides the engine
control module with all the information it needs
on road speed, cornering, coasting or traction
mode, and can respond optimally to any driving
situation.

Refer to SSP 89C303, Volkswagen
R32, for more information.

Characteristics of the Haldex coupling:

• Permanent all-wheel drive with
electronically controlled multi-plate clutch

• Front drive characteristic

• Quick response

• No strain on clutch when parking and
maneuvering vehicle

• Compatible with different tires (e.g.,
emergency wheel)

• No restrictions on towing with the rear
axle on the ground

• Fully integrates with systems such
as the Anti-Lock Brake System (ABS),
Electronic Differential Lock (EDL), Anti­Slip Regulation (ASR), Electronic Brake
Distribution system (EBD), and Electronic
Stabilization Program (ESP)

Haldex Coupling

66

All-Wheel Drive Systems

The Haldex coupling is mounted on the rear axle
differential and is driven by the drive shaft.

Engine torque is transmitted to the drive shaft
through the gearbox, the front axle differential,
and the front axle drive.

The drive shaft is connected to the input shaft of
the Haldex coupling. In the Haldex coupling, the
input shaft is separated from the output shaft to
the rear axle differential.

Torque can only be transmitted to the rear axle
differential when the Haldex coupling clutch
plates are engaged.

Drive Shaft

Haldex Coupling

Rear Differential

Transmission

Rear Differential

Drive Shaft

Haldex Coupling

67

Tools

Sirometer (Vibratach)

The sirometer is a tool that is useful when
diagnosing NVH concerns. Originally used for
reading small engine rpm, this inexpensive
tool is highly accurate for measuring vibration
frequencies. The sirometer has enough range
to measure the majority, if not all, of an
automobile’s vibration frequencies. The tool can
be purchased at most full service small engine
repair and parts centers.

The sirometer has a wire that, when adjusted
to the proper length, resonates to the vibration
frequency. To use the sirometer, hold it against
a vibrating component. Rotate the dial to
extend the wire and change the wire’s resonant
frequency until the wire vibrates at its widest
arc. Then read the frequency on the tool’s face,
labeled Cycles Per Second – Hertz.

Always adjust the length of the wire from its
smallest length to its longest length to ensure
all frequencies are being recorded. It is possible
to have more than one vibration present in a
vehicle.

68

Tools

90018542

EVA II™

The EVA II allows for a systematic collection
of information that is necessary to accurately
diagnose and repair NVH problems. The proper
use of the EVA II can significantly reduce vehicle
service time. The tool uses an electronic pick­up that measures vibration frequency and
amplitude. An additional pick-up can be added
and two sources of vibrations can be compared.
The pick-ups can be placed anywhere on the
vehicle. By placing the pick-up on different areas
of the vehicle and comparing the vibration’s
amplitude, as displayed on the screen, the
source of the vibration can be located by the
highest amplitude. If the steering wheel or
passenger’s seat is vibrating, the pick-up can be
placed there to measure the vibration.

The EVA II contains a software database that
contains most tire sizes and axle gear ratios.
When the correct vehicle information is entered
into the EVA II, the tool will determine and
display the source(s) of the vibration. This
feature eliminates most of the mathematical
formulas and calculates the known frequencies
of rotating components.

The EVA II can record snapshots during a road
test and the data replayed to determine the
vibration frequency. This is useful for intermittent
or short duration vibrations.

The EVA II has feature to use an inductive
pick-up timing light to visually flash a vibration
frequency. The operation manual for the tool
describes how to use this feature to help in
diagnosing the location of a vibration’s source.
The flashing timing light can be used to balance
propeller shafts.

Contact Equipment Solutions for more
information on the EVA II.

69

Tools

ChassisEAR™

The ChassisEAR is a versatile electronic
listening tool that allows the user to listen
to amplified sounds through a professional
set of headphones. The proper use of the
ChassisEAR can reduce the time in diagnosing
NVH concerns on a vehicle. The tool has
multiple microphone inputs that can be placed
in different sections of the vehicle. Attachment
of the six microphones and clamps helps to
locate many difficult-to-diagnose vehicle parts.
During a road test, these parts do not make
the same sounds as when the car is on a
hoist. To accurately diagnose an under-vehicle
problem, operate the vehicle so all parts and
bearings are under full load. The different inputs
allow the loudest area to be determined and
thus determine the possible source. Place the
microphones on parts or areas suspected as
being the possible source. Some of these
vehicle parts and areas include:

Remember that noises can be caused from
a vibration that resonates through another
component causing it to vibrate. Always check
for a vibration frequency when beginning to
diagnose a noise concern.

Contact Equipment Solutions for more
information on the ChassisEAR.

• Wheel bearings

• Brake calipers

• CV joints

• Leaf and coil springs

• Differential

• Transmission

• Body squeaks and rattles

• Under dash

• Fuel injectors

• Generator

• Water pump

• Smog pump

• Power steering pump

• Air conditioning compressors

70

Hunter's GSP9700 Service Vibration
Control System™

The Hunter GSP9700 Series Vibration Control
System is an electronic dynamic balancer. The
GSP9700 measures tire and wheel assembly
balance, runout, and radial force variation
measurement (road force variation (RFV)
measurement).

Tools

71

Tools

90018567

Other Tools

Several automotive tool manufacturers have
developed electronic tools for measuring and
recording noises and vibrations. Some of these
tools have multiple vibration and noise inputs,
recording and graphing capabilities. Not all of
the tools available have been covered.

Please contact automotive tool manufacturers to
request information.

72

NVH Terminology

Glossary

Audible Range of Sound – Sounds that are in

the range of 20 to 20,000 Hertz (Hz).

Amplitude – The vertical measurement
between the top and bottom of a wave. Also
see magnitude.

Beat – An NVH concern produced by two
sounds that is most noticeable when the
frequency difference is 1 to 6 Hz.

Bead Seating – The process of seating the
tire to the rim. If properly lubricated the bead
seating occurs when the tire and wheel are
assembled.

Compelling Force – A vibrating object acting
upon another object that causes the other
object to vibrate.

Cycle – The path a wave travels before the wave
begins to repeat the path again.

Dampen – To reduce the magnitude of a noise
or vibration.

Dampers – A component used to dampen
a noise or vibration. Foam and rubber are
commonly used to dampen vibrations.

Dynamic Balance – A procedure that balances a
tire and wheel assembly in two planes. Dynamic
balance removes radial and lateral vibrations.

Droning, High-Speed – A long duration, non­directional humming noise that is uncomfortable
to the ears and has a range of 50 mph (80.5 kph)
and up.

Droning, Low-Speed – A long duration, low­pitched noise that is non-directional and has a
range of up to 30 mph (48 kph).

Droning, Middle-Speed – A long duration, low­pitched noise that is non-directional and has a
range of 30 to 50 mph (48 to 80.5 kph).

Electronic Vibration Analyzer II (EVA II) – An
electronic NVH diagnostic tool that measures
frequency and amplitude.

Frequency – The number of complete cycles
that occurs in a given period of time.

Harshness – An aggressive suspension feel or
lack of give in response to a single input.

Hertz – The unit of frequency measurement
in seconds (a vibration occurring 8 times per
second would be an 8 Hz vibration).

Intensity – The physical quality of sound that
relates to the amount and direction of the flow
of acoustic energy at a given speed.

Lateral Runout – A condition where a rotating
component does not rotate in a true plane. The
component moves side-to-side (wobbles) on its
rotational axis.

Magnitude (Amplitude) – The amount of force
or the intensity of the vibration. The magnitude
or strength of a vibration is always greatest at
the point of resonance.

Medium – Provides a path for sound waves to
travel through.

Natural Frequency – The frequency that a
component will vibrate the easiest. Normally,
the larger the mass, the lower its natural
frequency.

• Engine block (2-4 Hz)

• Tire and wheel assemblies (1-15 Hz) –
proportional to vehicle speed

• Suspension (10-15 Hz

• Driveline (20-60 Hz)

• Differential components (120-300 Hz)

Noise – The unpleasant or unexpected sound
created by a vibrating object.

Order – The number of disturbances created in
one revolution of a component.

Phase – The position of a vibration cycle relative
to another vibration cycle in the same hertz rate
(time frame).

73

Glossary

Phase – The cycle pattern of two or more

vibrations that overlap and combine to increase
or decrease the overall magnitude.

Pitch – The physical quality of sound that relates
to the frequency of the wave.

Radial Force Variation (RFV) – A measurement
of the tire’s uniformity, under load, in regards
to the variation of the load acting towards the
center of the tire; commonly referred to as the
tire's sidewall variation.

Radial Runout – A condition where a rotating
component does not rotate in a true plane. The
component moves up and down on its rotational
axis.

Resonance – The tendency of a system to
respond increasingly to a compelling force
oscillating at, or near, the natural frequency of
the system. This causes a sudden and large
vibration.

Static Balance – The method of balancing a tire
and wheel assembly in a single plane. Static
balancing removes only the lateral (side to
side, wobble) imbalance and the tire and wheel
assembly could possibly have a radial (up and
down) vibration.

Torque Sensitive Vibration or Noise – A
vibration or noise that is sensitive to different
loads and torque, applied to the drive train of a
vehicle. The vibration or noise changes when the
throttle position or transmission gearing is used,
during a road test, to change the torque applied
to the drive train.

Vibration – The repetitive motion of an object,
back and forth or up and down, which may be
felt or heard.

Wheel Diameter – The dimension of a wheel
measured on the inside of the wheel at the
bead seat area.

Road Noise – A noise that occurs while driving
on gravel or roughly paved roads at all vehicle
speeds, or when a vehicle is coasting.

Shake, Lateral – A side-to-side vibration of the
body, seats, and steering wheel.

Shake, Vertical – An up and down vibration of
the body, seats, and steering wheel.

Shimmy, High-Speed – A vibration that causes
the steering wheel to oscillate when driving on
smooth roads at high speeds.

Shimmy, Low-Speed – A vibration that causes
the steering wheel to oscillate when driving
across a bump at low speeds.

Source Component – The component that is
diagnosed as being the root cause of a vibration
or noise concern.

Sound – The result of a vibrating disturbance of
an object, which produces waves that transmit
out from the source.

74

Diagnostic Flow Chart

Felt while braking

Vibration is felt at a certain

vehicle speed

Diagnose according to conditions listed below

Road test to verify concern

Is it felt through the steering wheel? – Start with front axle

Concern disappears or is

diminished after the car

has been driven awhile

Vibration is felt at a certain

engine speed

Check tires for Temporary

Flat-Spotting:

Tires can become temporary

flat-spotted when a vehicle

has been driven and then

parked on a cold surface. This

may happen in cold climates

as well as warm climates.

Vehicles parked for long

periods of time and/or stored

with low air pressure are also

susceptible to flat spotting.

Is it felt through seat/vehicle floor pan? – Start with rear axle

Check vehicle history prior to diagnosis and use NVH SSP for in-depth diagnosis.

Check wheels for:

• Dirt, mud, snow, or ice build-up

• Damage

• Missing or excessive wheel

weights

• Loose wheel bolts

• Proper wheel torque

• Excessive runout

Check tires for:

• High Radial Force

Variation (RFV)

• Imbalance

• Irregular wear

• Abnormal pressure

Check drive train for:

• Prop shaft misalignment

• Damaged axle shafts/CV joints

• Worn wheel bearings

• Rear differential performance

Check drive train for:

• Prop shaft misalignment

• Damaged axle shafts

• Damaged CV joints

• Rear differential performance

• Proper torque converter

performance

Check Engine for:

• Misfires

• Accessory vibrations

• Camshaft, crankshaft and

intermediate shaft imbalance

Check Chassis for:

• Damaged or misaligned engine

and transmission mounts

• Proper Electro-Hydraulic mount

operation

• Damaged or misaligned

exhaust system and

components

Check:

• Brake components

• Steering components

• Suspension

components

• Relevant Technical

Bulletins

75

Knowledge Assessment

An online Knowledge Assessment (exam) is available for this Self-Study Program.

The Knowledge Assessment may or may not be required for Certification.

You can find this Knowledge Assessment at:

www.vwwebsource.com

From the vwwebsource.com Homepage, do the following:

– Click on the Certification tab

– Type the course number in the Search box

– Click “Go!” and wait until the screen refreshes

– Click “Start” to begin the Assessment

For assistance, please call:

Certification Program Headquarters

1-877-CU4-CERT
(1-877-284-2378)

(8:00 a.m. to 8:00 p.m. EST)

Or, E-mail:

Comments@VWCertification.com

77

Notes

78

Volkswagen of America, Inc.
3800 Hamlin Road
Auburn Hills, MI 48326
Printed in U.S.A.
March, 2005