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.
Avariety ofASA-5®slack adjuster confi 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 defl ection, drum and foundation brake component distortion, or brake component wear.
The ASA-5®slack adjuster incorporates a clutch-type adjuster mechanism that continuously adjusts in very small increments as lining and drum wear occurs. The adjustments made by the ASA-5®slack adjuster are, therefore, not in specifi c increments relative to actuator stroke.
YOKE
YOKE PIN
LINK PIN
LINK
BOOT
LUBE
FITTING
WORM
GEAR
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 theASA-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
