®
Bendix Piggyback Spring Brake
SERVICE PUSH-ROD
SERVICE
CHAMBER
SD-02-4500
SERVICE
DIAPHRAGM
FIGURE 1 - BENDIX PIGGYBACK SPRING BRAKE
DESCRIPTION
The Bendix Piggyback Spring Brake is made up of a
conventional brake chamber and an emergency or parking
spring mechanism for use on vehicles equipped with cam
foundation brakes. The S pring Brake Actuator provides: (1)
Service Braking, (2) Parking and (3) Emergency Braking.
The actuator can be piped with various system arrangements
to be automatically or manually applied under emergency
braking conditions.
The spring brake is a diaphragm type actuator which converts
the energy of air pressure into mechanical force. The
diaphragm is held between the pressure plate and nonpressure plate by a two piece clamp ring.
Different size brake chambers are identified by numbers
which specify the effective area of a diaphragm. For example,
a T ype 30/30 Spring Brake has 30 square inches of ef fective
area on each diaphragm.
The standard diaphragm material is a compound of natural
rubber with a fabric interior of nylon.
PIGGYBACK CHAMBER
PREVENTIVE MAINTENANCE
Important: Review the warranty policy before performing
any intrusive maintenance procedures. An extended warranty
may be voided if intrusive maintenance is performed during
this period.
Because no two vehicles operate under identical conditions,
maintenance intervals will vary . Experience is a valuable guide
in determining the best maintenance interval for a vehicle.
WARNING!
Piggyback Spring Brake Chambers contain a loaded
compression spring. Property damage, serious injury
or death may occur if instructions are not followed
completely.
Every 300 operating hours, 8,000 miles, or one (1) month:
1. Check push rod travel and adjust travel at the slack
adjuster if needed. Push rod travel should be as short
as possible without the brakes dragging. Excessive push
rod travel reduces braking efficiency , shortens diaphragm
life, gives slow braking response and wastes air.
1
2. Check push rod to slack adjuster alignment from release
to full stroke position to be sure the push rod moves out
and returns properly without binding at the non-pressure
plate hole or with other structures. Also check the angle
formed by the slack adjuster arm and push rod. It should
be greater than 90 degrees when the chamber is in the
released position and approach 90 degrees at maximum
readjustment stroke.
3. Check tightness of mounting nuts. Torque on the nonpressure plate mounting nuts should be 1 10 ft/lbs.
4. Check cotter pins to ensure they are in place.
5. Check all hoses and lines. They should be secure and
in good condition with sufficient length to allow for axle
movement.
Every 3,600 operating hours, 100,000 miles or one (1) year:
1. Disassemble and clean all parts. Clean all metal parts
in cleaning solvent, removing all rust and scale. Carefully
inspect all metal parts for cracks, distortion or damage.
All diaphragm sealing surfaces should be smooth and
clean.
2. Install new diaphragm or any other parts if they are worn
or deteriorated. Perform steps outlined in "Replacing the
Service Diaphragm". When the diaphragm, spring, or
both are replaced, they should be replaced in the
corresponding chamber on the same axle.
WARNING!
A piggyback spring brake chamber cannot have the
emergency diaphragm replaced. Replace the whole
piggyback spring brake chamber.
OPERATION & LEAKAGE TESTS
OPERATING TEST
1. Apply brakes and observe that the push rods move out
promptly and without binding.
2. Release brakes and observe that the push rods return to
the released position promptly and without binding.
3. Check push rod travel. Push rod travel should be as
short as possible without brakes dragging. Adjust travel
of push rod at slack adjuster if necessary .
LEAKAGE TEST
1. Make and hold a full brake application.
2. Using soap solution, coat clamping ring(s). If leakage is
detected, tighten clamping ring only enough to stop
leakage. DO NOT OVERTIGHTEN as this can distort
the sealing surface or clamping ring. Coat area around
push rod hole (loosen boot if necessary). No leakage is
permitted. If leakage is detected, the diaphragm must
be replaced.
2
SERVICE
PORT
SERVICE
PUSH ROD
LOCKNUT
COTTER PIN
FIGURE 2 - PIGGYBACK SPRING BRAKE DIAGRAM
EMERGENCY
PORT
MOUNTING
NUT
YOKE
WARNING! PLEASE READ AND FOLLOW
THESE INSTRUCTIONS TO AVOID
PERSONAL INJURY OR DEATH:
When working on or around a vehicle, the following
general precautions should be observed at all times.
1. Park the vehicle on a level surface, apply the parking brakes, and always block the wheels. Always
wear safety glasses.
2. Stop the engine and remove ignition key when
working under or around the vehicle. When working in the engine compartment, the engine should
be shut off and the ignition key should be removed.
Where circumstances require that the engine be
in operation, EXTREME CAUTION should be used
to prevent personal injury resulting from contact
with moving, rotating, leaking, heated or electrically charged components.
3. Do not attempt to install, remove, disassemble or
assemble a component until you have read and
thoroughly understand the recommended procedures. Use only the proper tools and observe all
precautions pertaining to use of those tools.
4. If the work is being performed on the vehicle’s air
brake system, or any auxiliary pressurized air systems, make certain to drain the air pressure from
all reservoirs before beginning ANY work on the
vehicle. If the vehicle is equipped with an AD-IS
air dryer system or a dryer reservoir module, be
sure to drain the purge reservoir.
™
MAIN SPRING
EMERGENCY
DIAPHRAGM
NON-PRESSURE
HOUSING
FIGURE 3 - PIGGYBACK SPRING BRAKE CUT -AWA Y VIEW
PORT
RELEASE
TOOL
SIDE
POCKET
PUSH ROD
5. Following the vehicle manufacturer’s recommended procedures, deactivate the electrical system in a manner that safely removes all electrical
power from the vehicle.
6. Never exceed manufacturer’s recommended
pressures.
7. Never connect or disconnect a hose or line containing pressure; it may whip. Never remove a component or plug unless you are certain all system
pressure has been depleted.
8. Use only genuine Bendix® replacement parts, components and kits. Replacement hardware, tubing,
hose, fittings, etc. must be of equivalent size, type
and strength as original equipment and be
designed specifically for such applications and
systems.
9. Components with stripped threads or damaged
parts should be replaced rather than repaired. Do
not attempt repairs requiring machining or welding unless specifically stated and approved by the
vehicle and component manufacturer.
10. Prior to returning the vehicle to service, make
certain all components and systems are restored
to their proper operating condition.
OPERATION: GENERAL
The Bendix Piggyback Spring Brake is made up of the service
chamber and the piggyback chamber. The Bendix Piggyback
Spring Brake provides service braking, parking, and
emergency braking.
The spring brake can be mounted with the mounting bolts in
either a vertical or horizontal plane on standard mounting
stud centers. T wo air lines are used: the service air line and
the emergency air line.
Controlled air pressure enters the service chamber through
the inlet port and acts upon the diaphragm moving the push
plate and rod assembly forward.
When the service chamber is used to actuate cam type
brake foundation assemblies, the yoke (which is threaded
on the push rod) is connected to a slack adjuster, which in
turn is connected to the brake cam shaft. This forward motion
of the push rod rotates the slack adjuster, cam shaft and
cam applying the vehicle brakes.
The greater air pressure admitted to the service chamber,
the greater the force applied by the push rod and, conversely ,
the less pressure applied to the service chamber the less
force applied by the push rod. Push rod force is determined
by multiplying the delivered air pressure by the effective
diaphragm area. For example, if 60 p.s.i. is admitted to a
type 30 service chamber, the lineal force on the end of the
push rod is approximately 1,800 lbs.
When air pressure is released from the brake chamber, the
push rod return spring in combination with the brake shoe
return spring returns the diaphragm, push plate and rod
assembly, slack adjuster and brake cam to their released
positions releasing the brakes.
When the driver operates the parking brake, air is exhausted
from the piggyback chamber. The main spring is allowed to
extend, which forces the push rod and the emergency
diaphragm forward. This forces the service diaphragm and
service push rod forward which applies the brakes.
When the air pressure in the piggyback chamber drops to
below 78 p.s.i., the main spring overcomes chamber
pressure and forces the push rod and emergency diaphragm
forward.
WARNING!
• Piggyback Spring Brake Chambers contain a
loaded compression spring. Property damage,
serious injury or death may occur if instructions
are not followed completely.
• When replacing the piggyback spring brake, make
sure to block the wheels to prevent vehicle
rollaway.
3
YOKE
LOCKNUT
SERVICE
RETURN SPRING
ADAPTER
RETURN SPRING
MAIN SPRING
RELEASE TOOL
SERVICE
DIAPHRAGM
FIGURE 4 - CAGING THE PIGGYBACK
• DO NOT service a piggyback spring brake
chamber if it has structural damage of any kind.
Replace the complete assembly. Dismount a
damaged piggyback spring brake by first cutting
the service push rod with an acetylene torch to
relieve any force it might have.
• Do not strike any part of a spring brake chamber
for any reason. This may cause structural
damage.
• Be careful not to drop a spring brake chamber
at anytime.
• A piggyback spring brake chamber cannot have
the emergency diaphragm replaced. Replace the
whole piggyback spring brake chamber.
• Always work from the side of the piggyback
spring brake chamber(s). Never work from the
front or back.
MECHANICAL RELEASE (CAGING) OF THE
BENDIX PIGGYBACK SPRING BRAKE
NOTE: The Bendix Piggyback Spring Brake Chamber is
not shipped caged. It must be caged prior to any work
being done.
1. Remove the dust cap from the keyhole in the center
of the piggyback spring brake chamber .
2. Remove the release tool assembly from the side
pocket of the adaptor base.
3. Insert the release tool (T-bolt) through the release tool
keyhole and into the pressure plate.
4. Turn the release tool 1/4 turn clockwise.
PRESSURE PLATE
EMERGENCY
DIAPHRAGM
5. Pull on the release tool to seat it in the pressure
plate properly.
6. Put on the release washer and nut.
7. To cage the main spring, tighten the release nut with a
hand wrench and ensure the service pushrod
is retracting.
8. Do not over torque the release tool assembly. Maximum
torque is 35 ft/lbs.
WARNING!
Do not use an impact wrench. An impact wrench may
over torque the release tool and cause damage to the
pressure plate.
9. The threaded portion of the release tool will extend
approximately 2.9 inches out of the nut when fully
released.
MECHANICAL RELEASE (CAGING) AND
REMOV AL OF THE PIGGYBACK SPRING BRAKE
CHAMBER TO BE REPLACED
NOTE: The piggyback spring brake chamber can be
replaced with the service brake chamber mounted to the
vehicle or removed for ease of access. To remove the
assembly from the vehicle, perform the steps outlined in
“Removal and Installation of the Combination Spring Brake.”
WARNING!
• Do not mechanically release (cage) the spring if
there is any structural damage to the brake. Caging
the spring in such a chamber may cause serious
injury or death. Replace the complete assembly.
4
• Do not remove the Piggyback Spring Chamber
Clamps.
1. Mechanically release the old piggyback spring brake by
following the original manufacturer’s instructions.
2. Ensure air pressure is removed from all air reservoirs
before removing the air hoses or working on the
spring brake.
3. Remove air hoses from the Piggyback spring brake
chamber. Be sure to mark both hoses to ensure
proper reinstallation.
4. Clamp a pair of vise grips around the service pushrod
touching the non-pressure housing. This cages the
service return spring.
5. Remove the clamp nuts and service clamp assembly
and carefully remove the old piggyback chamber.
INSTALLING THE BENDIX PIGGYBACK SPRING
BRAKE CHAMBER
1. Visually inspect the service diaphragm for excessive wear,
damage or cracks. Replace if needed. To replace the
service diaphragm, perform the steps outlined in
"Replacing the Service Diaphragm".
2. Line up the new piggyback spring brake chamber, the
service diaphragm, and the non-pressure housing,
ensuring that they are centered.
3. Reassemble the service clamp assembly. Ensure all
parts are seated properly and remain centered.
4. T orque the clamp nuts to 25 ft/lbs. Remove the vise grips
from the service push rod.
5. Reconnect the emergency air line to the emergency
porthole and reconnect the service air line to the
service porthole.
6. Pressurize the service half by putting air into the service
port. Do not exceed 120 psig. Test for leaks around the
clamps. No leaks are acceptable.
7. Uncage the main spring and return the release tool into
the release tool side pocket.
8. Replace the dust cap in the keyhole.
WARNING!
Check for proper service and emergency operation
after servicing any part of the brake chamber(s). Check
the brake adjustment if the combination spring brake
was removed/installed (Follow vehicle manufacturer’s
instructions to adjust the brakes).
REMOVAL AND INSTALLATION OF THE
COMBINATION SPRING BRAKE
WARNING!
Do not mechanically release (cage) the spring if there
is any structural damage to the piggyback spring brake
FIGURE 5 - PIGGYBACK CHAMBER
chamber. Caging the spring in such a chamber may
cause serious injury or death. Replace the complete
assembly.
REMOV AL:
1. Mechanically release (cage) the old piggyback spring
brake chamber by following the original manufacturer’s
instructions.
2. Ensure air pressure is removed from all air reservoirs
before removing the air hoses or working on the spring
brake.
3. Remove air hoses from the piggyback spring brake
chamber. Be sure to mark both hoses to ensure proper
reinstallation.
4. Remove the yoke pin, disconnect the yoke from the slack
adjuster, remove the mounting nuts, washer, and lock
washers and remove the combination spring brake. While
removing, use care to prevent the combination spring
brake from falling.
INST ALLATION:
1. Install the combination spring brake using the furnished
hardware. Torque the mounting nuts to 110 ft/lbs.
Connect the yoke to the slack adjuster and install the
yoke pin and the cotter pin.
2. Reconnect the emergency air line to the emergency
porthole and reconnect the service air line to the service
porthole.
3. Pressurize the service chamber by putting air into the
service port. Do not exceed 120 psig. Test for leaks
around the clamps. No leaks are acceptable.
5
RELEASE
TOOL
PIGGYBACK
SERVICE
CLAMP RING
SERVICE
DIAPHRAGM
FIGURE 6 - SERVICE DIAPHRAGM
NON-PRESSURE
CHAMBER
HOUSING
4. Uncage the main spring and return the release tool into
the release tool side pocket.
5. Replace the dust cap in the keyhole.
WARNING!
Check for proper service and emergency operation
after servicing any part of the brake chamber(s). Check
the brake adjustment if the combination spring brake
was removed/installed (Follow vehicle manufacturer’s
instructions to adjust the brakes).
2. Ensure that the piggyback spring brake chamber is
caged. To cage the piggyback spring brake chamber,
perform the steps outlined in either "Mechanical Release
of the Bendix Piggyback Spring Brake" or "Mechanical
Release of the Piggyback Spring Brake to be Replaced".
3. Mark the service clamp ring and non-pressure plate to
ensure proper alignment of parts during reassembly .
4. Remove the service clamp ring assembly and the
piggyback chamber. The service clamp ring is closest
to the non-pressure plate and slack adjuster. See
provided illustrations if in doubt.
WARNING!
Do not remove the spring chamber clamps.
5. Visually inspect the service diaphragm for excessive wear,
damage or cracks. Replace if needed.
6. Line up the piggyback spring brake chamber, the service
diaphragm, and the non-pressure housing, ensuring that
they are centered.
7. Reassemble the service clamp assembly. Ensure all
parts are seated properly and remain centered.
8. T orque the clamp nuts to 25 ft/lbs. Remove the vise grips
from the service push rod.
9. Reconnect the emergency air line to the emergency
porthole and reconnect the service air line to the
service porthole.
10.Pressurize the service half by putting air into the service
port. Do not exceed 120 psig. Test for leaks around the
clamps. No leaks are acceptable.
1 1. Uncage the main spring and return the release tool into
the release tool side pocket.
12.Replace the dust cap in the keyhole.
REPLACING THE SERVICE DIAPHRAGM
To replace the service diaphragm, it is not necessary to
remove the complete combination spring brake from the
vehicle. However, it can be removed for ease of access. T o
remove the combination spring brake, perform the steps
outlined in "Removal and Installation of the Combination
Spring Brake".
WARNING!
• A piggyback spring brake chamber cannot have
the emergency diaphragm replaced. Replace the
whole piggyback spring brake chamber.
1. Protect the service push rod with tape, and lock the vise
grips on the push rod close to the non-pressure plate.
(This will hold the rod in the applied position).
6
BW2106 © 2004 Bendix Commercial Vehicle Systems LLC 8/2004. All rights reserved. Printed in U.S.A.
WARNING!
Check for proper service and emergency operation
after servicing any part of the brake chamber(s). Check
the brake adjustment if the combination spring brake
was removed/installed (Follow vehicle manufacturer’s
instructions to adjust the brakes).
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