BENDIX SD-05-1269 User Manual

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 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

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

slack adjuster conﬁ gurations are offered

slack adjuster. Note: The manual adjuster

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 deﬂ ection, drum and foundation brake component distor tion, or brake component wear.

The ASA-5 adjuster mechanism that continuously adjusts in very small increments as lin ing and drum wear occurs. The

adjustments made by the ASA-5 therefore, not in speciﬁ c increments relative to actuator stroke.

slack adjuster incorporates a clutch-type

slack adjuster are,

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 ﬁ 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

ADAPTER BUSHING

YOKE

YOKE PIN

LINK PIN

CLUTCH SPRING

WORM

ANTI-

REVERSE

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.

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

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 a Bendix® 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 p r ocedures, 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.

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® brand replacement parts, compon ents and kits. Replaceme nt hardware, tubing, hose, ﬁ ttings, etc. must be of equivalent size, type and strength as original equipment and be designed speciﬁ 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 speciﬁ 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.

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 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

slack adjuster on the

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 ﬁ rm. Replace parts that are suspect.

4. W i r e b r us h the found a t i on 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 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 ﬂ ush

slack adjuste r on the brake

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

FIGURE 6 - INSTALLATION ANGLE

Slack Adjuster

Arm Length Angle

5" 99°-113°

5.5" 98°-111°

6" 90°-109°

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