Bendix Commercial Vehicle Systems ASA-5 AUTOMATIC SLACK ADJUSTER 2/11 User Manual

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Bendix® ASA-5® Automatic Slack Adjuster

SD-05-1269

DESCRIPTION

The Bendix® ASA‑5® automatic slack adjuster is designed
for use on cam actuated drum brakes of the type in use
on most highway vehicles. Like a manual slack adjuster,
the ASA‑5® slack adjuster multiplies and transforms
the linear force of the air actuator into a rotational force
or torque which is used to apply the foundation brake.
Additionally, the ASA‑5® slack adjuster automatically
adjusts the clearance between the brake lining and drum
to compensate for wear.

A variety of ASA‑5® slack adjuster congurations are offered
including both straight arm and 5/8" yoke offset models.
The ASA‑5® slack adjuster is offered in arm lengths of 5,
5‑1/2 and 6 inches and worm gear splines to accommodate
the standard 1‑1/4" and 1‑1/2" SAE 10C, 24, 28 and 37
tooth splines.

Either of two yoke designs (easy‑on and quick connect)
in combination with an external manual adjuster hex
provides for convenient installation and maintenance of
the ASA‑5® slack adjuster. Note: The manual adjuster

hex is intended for use during installation. CAUTION:
Automatic slack adjusters should not be adjusted
manually to correct excessive pushrod stroke.

YOKE

YOKE PIN

LINK PIN

LINK

BOOT

LUBE

FITTING

WORM

GEAR

OPERATION

GENERAL

The automatic adjustment provided by the Bendix®
ASA‑5® slack adjuster results in consistent brake lining to

drum clearance and brake actuator stroke. The key to its
operation is the ability to complete the brake adjustment
during the early part of each brake application and to cease
adjusting as resistance to brake cam rotation begins to
build. This aspect of the adjuster mechanism’s operation
prevents over‑adjustment caused by lining compression,
actuator bracket deection, drum and foundation brake
component distor tion, or brake component wear.

The ASA‑5® slack adjuster incorporates a clutch‑type
adjuster mechanism that continuously adjusts in very
small increments as lin ing and drum wear occurs. The

adjustments made by the ASA‑5® slack adjuster are,
therefore, not in specic increments relative to actuator
stroke.

FIGURE 1 - ASA-5® AUTOMATIC SLACK ADJUSTER

BRAKE APPLICATION

When the brakes are applied, the linear travel of the brake
actuator’s push rod causes the ASA‑5® slack adjuster to

rotate the foundation brake camshaft which in turn begins
to force the brake shoes into contact with the drum. When

the ASA‑5® slack adjuster rotates, the yoke assembly pivots
on the yoke pin causing the link to be pulled upward.

The “teeth” on the link mesh with the adjuster mechanism
pinion. As the link is pulled it travels rst through its free
play and then causes the pinion to rotate. Rotation of the
pinion is transmitted through the clutch spring to the worm
and shaft. Worm and shaft rotation results in worm gear
rotation which in turn adjusts (or repositions) the brake
camshaft.

When the foundation brake shoes contact the drum, the
camshaft begins to resist rotation and friction between the
worm gear and worm builds, preventing further rotation

1

ADAPTER
BUSHING

YOKE

YOKE PIN

LINK PIN

CLUTCH
SPRING

WORM

ANTI-

REVERSE

SPRING

SPRING

RETAINER

WORM

GEAR

FIGURE 2 - SECTIONAL VIEW OF PROFILE AND END

BOOT

LUBE

RELIEF

OPENING

FREE

PLAY

MANUAL

ADJUSTER

HEX

LUBE

FITTING

PINION

of the worm. Brake adjustment ceases at this point and
further rotation of the ASA‑5® slack adjuster will cause the

pinion and clutch spring to slip. The “free play” between
the link teeth and pinion results in a predetermined lining
to drum clearance.

BRAKE RELEASE

When the brake application is released, the brake actuator
push rod returns the ASA‑5® slack adjuster to the released
position. During release, the ASA‑5® slack adjuster rotates
back toward the actuator causing the brake camshaft to
again rotate, but in the opposite direction, and the brake
shoes begin to move away from the drum. As the ASA‑5®
slack adjuster rotates back to the release position the yoke
again pivots causing the link to be pushed downward into
the slack adjuster body. The “free play” between the link
teeth and pinion is taken up during the initial part of the
release. Continued movement of the ASA‑5® slack adjuster
toward the released position causes the link to rotate the
pinion. The anti‑reverse spring prevents counterclockwise
rotation of the shaft and worm causing the pinion and clutch
spring to slip. The gripping action of the anti‑reverse spring
and slip page of the clutch spring during release is due to
the direction of the coil windings of each.

2

YOKE DESIGNS

ASA‑5® slack adjusters may be equipped with either of two
yoke designs. Both are designed to permit installation or
removal of the slack adjuster along with its yoke body and
its attached adjusting linkage.

The brake actuator push rod must thread into the adapter
a minimum of 1/2 inch and must not extend more than
7/64 inch beyond the other end of the adapter. The yoke
adapters (quick connect & easy‑on) have either a 1 or
1‑1/4 inch hex to allow tightening of the brake actuator
push rod jam nut.

EASY-ON YOKE (REFER TO FIGURE 3)

The easy‑on yoke assembly consists of an adapter which
is threaded internally to match the push rod threads and
externally to match female threads in the yoke. A special
extended yoke adapter is also available as a separate
service item. The extended adapter is 1/2 inch longer than
the standard and is primarily intended for use when the
existing brake actuator push rod is too short.

PUSH ROD

1-5/16"

YOKE

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.

JAM NUT

MOUNTING

STUD

ADAPTER

FIGURE 3 - EASY-ON YOKE ASSEMBLY

3/8" OUT

QUICK-CONNECT YOKE

The adapter bushing in this case is threaded internally to
match the push rod, but is designed to slide into the yoke.
A retainer ring is used to secure the adapter bushing in the
yoke. (Refer to Figure 4.)

PUSH ROD

RETAINING RING

1"

YOKE

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.

5. F o l lo w i n g t h e ve h ic l e ma n u f ac t ur e r ’s
re c ommended pro cedures, dea c tivate 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.

JAM NUT

MOUNTING

STUD

ADAPTER
BUSHING

FIGURE 4 - QUICK-CONNECT YOKE ASSEMBLY

FLUSH

GENERAL SAFETY GUIDELINES
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.

8. Use only genuine Bendix® replacement parts,
components and kits. Replacement hardware,
tubing, hose, ttings, etc. must be of equivalent
size, type and strength as original equipment and
be designed specically 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 specically 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.

11. For vehicles with Antilock Traction Control
(ATC), the ATC function must be disabled (ATC
indicator lamp should be ON) prior to performing
any vehicle maintenance where one or more
wheels on a drive axle are lifted off the ground

and moving.

3

INITIAL INSTALLATION PREPARATION

1. If necessary, carefully remove the manual or automatic
slack adjuster currently installed, including the brake
chamber yoke assembly.

2. Before mounting the ASA‑5® slack adjuster on the
camshaft, check the brake chamber push rod length
to determine whether shortening or replacement is
required. To accomplish this:

A. With the brake chamber in the released position,

place a square (or equivalent object) so that one
edge is parallel to the actuator push rod while the
other edge bisects the brake camshaft. Measure
the distance from the push rod end to the vertical
edge of the square and compare it to the values in
Figure 5.

B. If the measurement is less than the minimum shown

in Figure 5, the brake actuator push rod must be
shortened. If the measurement is greater than the
maximum values, the brake actuator push rod
may require replacement. The extended adapter,
available as a separate service part (5/8"‑18 pc. no.
297700 and 1/2"‑20 pc. no. 297701) may avoid the
need to replace the brake actuator push rod. The
extended adapter is available for the easy‑on yoke
assembly only. Note: Installing any other type of
push rod extender is not recommended, because
these devices may loosen over time and result in
an improperly adjusted brake.

BRAKE ACTUATOR

PUSH ROD

SQUARE

3. Inspect the foundation brake, brake chamber and related
components. Make certain the camshaft bushings and
seals are not excessively worn. Lubricate the camshaft
bushings. Check the brake chamber bracket for cracks
and excessive corro sion. The brake actuator push rod
should not be loose or bent and the return spring should
be rm. Replace parts that are suspect.

4. W i r e b r us h the foun d a t io n b r ak e camshaft to
loosen contamination and wipe clean. Depending on
environmental conditions, an application of anti‑ seize
compound to both the camshaft and worm gear spline
may facilitate later slack removal.

INSTALLATION

1. Select the proper ASA‑5® slack adjuster.

2. Install the AS A‑5® slack adjuste r on t he brak e
camshaft.

3. If the ASA‑5® slack adjuster has the easy‑on yoke (see
Figure 3), position the brake actuator push rod jam nut
ap proximately 1‑5/16 inches from the end of the brake
actuator push rod. Thread the easy‑on yoke adapter on
the brake actuator push rod until it is approximately 3/8
inch from the end of the brake actuator push rod end.
Turn the ASA‑5® slack adjuster manual adjustment hex
clockwise until the adapter extends into the threaded
bore of the yoke approximately 1/8 inch. Thread the
adapter into the yoke and tighten to 10 foot pounds.

The installation angle of a properly installed ASA‑5®

slack adjuster:

4. If the ASA‑5® slack adjuster has the quick connect yoke
(see Figure 4), position the brake actuator push rod
jam nut approximately 1 inch from the end of the brake
ac tuator push rod. Thread the quick connect adapter
bushing on the brake actuator push rod until it is ush

DISTANCE

"A"

MOUNTING

STUD

SLACK "A" STD. "A"
ADJUSTER QUICK CONNECT EXTENDED
ARM OR EASY-ON EASY-ON
LENGTH ADAPTER ADAPTER

5" 1-15/16" - 3-1/32" 2-7/16" - 3-17/32"

5-1/2" 1-15/16" - 3-3/16" 2-7/16" - 3 11/16"

6" 1-3/16" - 3-3/16" 1-11/16" - 3-11/16"

FIGURE 5 - MEASURING THE BRAKE ACTUATOR PUSH
ROD

4

FIGURE 6 - INSTALLATION ANGLE

Slack Adjuster

Arm Length Angle

5" 99°‑113°

5.5" 98°‑111°

6" 90°‑109°