Bendix Commercial Vehicle Systems ASA-5 AUTOMATIC SLACK ADJUSTER 2/11 - 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 configurations 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 deflection, 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 specific 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 first 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