User's Manual

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SD-05-1269

Bendix

ASA-5

Automatic Slack Adjuster

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.

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.

BOOT

LINK

LINK PIN

YOKE PIN

YOKE

WORM

GEAR

LUBE

FITTING

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

Summary of content (12 pages)

PAGE 1
SD-05-1269 ® Bendix® ASA-5® Automatic Slack Adjuster DESCRIPTION YOKE 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.
PAGE 2
YOKE ADAPTER BUSHING YOKE PIN LINK PIN CLUTCH SPRING WORM ANTIREVERSE SPRING BOOT LUBE RELIEF OPENING FREE PLAY PINION SPRING RETAINER WORM GEAR MANUAL ADJUSTER HEX LUBE FITTING FIGURE 2 - SECTIONAL VIEW OF PROFILE AND END 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.
PAGE 3
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.
PAGE 4
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.
PAGE 5
with the end of the brake actuator push rod. Install the retaining ring on the adapter bushing, making certain it is in the adapter bushing groove. Turn the ASA‑5® slack adjuster manual adjustment hex clockwise until the adapter bushing begins to enter the yoke. Fully compress the retaining ring “legs” and continue turning the ASA‑5® slack adjuster manual adjustment hex until the adapter bushing is completely in the yoke. Allow the retaining ring to expand into the corresponding groove in the yoke.
PAGE 6
ADJUSTER HEX ROTATES CLOCKWISE DURING ADJUSTMENT STRAIGHT LINE SCRIBED ACROSS HEX AND BODY FIGURE 7 - TESTING ADJUSTER MECHANISM pressure for this test can be achieved as follows: Build the system pressure up to 100 psi reading on the vehicle gauge. Shut the engine off. Fan the brakes to attain a 90‑95 psi reading. Make and hold a full brake application while the strokes are checked. 4. The Bendix® SureStroke™ indicator is also available as a visual stroke indicator.
PAGE 7
and COMPLETE RELEASES (the number of applications depends on how much the slack was de‑adjusted). BRAKE MAINTENANCE INSPECTION Note: Make certain the vehicle has been prepared according to the instructions under the heading GENERAL SAFETY GUIDELINES. The following test can be used to inspect the maintenance condition of the foundation brake and to determine how much of the chamber stroke is caused by the condition of the foundation brake. 1. Always chock the wheels to keep vehicle from moving. 2.
PAGE 8
CLEANING AND INSPECTION 1. Inspect the worm gear camshaft splines for damage. If damaged, replace the ASA‑5® slack adjuster. 2. Clean and inspect the yoke pin and link pin holes in the yoke, adjuster link and slack adjuster body. The holes should be visually round with no perceptible “egg shaping.” A new yoke pin and link pin can be used to make this inspection. If this condition is noted, the affected part must be replaced. 3. Clean out the retaining ring grooves in the yoke. REASSEMBLY 1.
PAGE 9
ASA-5® SLACK ADJUSTER TROUBLESHOOTING CHART REMEDY SYMPTOMS CAUSE 1. Brake Actuator stroke is too long. A. Loose actuator push rod jam nut. A. Reposition components and torque to specification. B. Excessive clearance between adapter/ adapter bushing and yoke due to wear. B. Replace damaged or worn parts. C. Excessive clearance between components: yoke pin—yoke C. Replace worn parts.
PAGE 10
ASA-5® SLACK ADJUSTER TROUBLESHOOTING CHART (Continued) CAUSE REMEDY A. ASA‑5® slack adjuster improperly installed. Too close to actuator: brakes can’t fully release. A. Correct the ASA‑5® slack adjuster installation. B. Loose actuator push rod jam nut. B. Reposition components and torque to specification. C. Spring brakes not fully retracting. C. Check spring brake release air pressure and repair or replace air valving as necessary. Repair or replace spring brake. D.
PAGE 11