UNDERCARRIAGE TMS700E SERVICE MANUAL
8-30 Published 01-29-2015, Control # 512-01
into the web holes. Make sure that both loops are
engaged in the web holes.
g. Repeat steps (d) thru (f) on the upper shoe.
7. Install the drum and axle spindle nut(s) and washers.
AUTOMATIC SLACK ADJUSTER
Description
The automatic slack adjuster compensates for normal wear
in the brake shoe linings by maintaining a nominal clearance
between the lining and drum. They are preset at the
manufacturer’s facility.
When the brake is applied the slack adjuster’s rotation
moves the shoes and linings into contact with the brake
drum. This movement also lifts the actuation rod through a
pre-set, free travel dimension that is normal lining to drum
clearance. Continuing the brake application rotates a one-
way clutch in its over riding mode, and at the same time
causes the large coil spring to deflect at a specific force. This
spring deflection allows the worm to move axially. The clutch
movement is restricted by a machine step. This movement
fully disengages the drive clutch from the worm and prevents
unwanted brake adjustment from occurring.
When the brake is released, the large coil spring resumes its
original load and position, which allows the drive clutch to re-
engage. Simultaneous to drive clutch re-engagement, if any
lining wear has occurred, the actuation rod rotates the one
way adjuster clutch an amount proportional to lining wear.
This motion rotates the worm, worm wheel, and the S-cam
shaft resulting in adjustment of the brakes.
Maintenance
Alternative 1
NOTE: If your slack adjuster is as pictured in Figure 8-24,
use the removal, installation and adjustment
procedures that follow. Refer to Alternative 2,
page 8-34 for the other type of slack adjuster.
Removal
1. Disengage the pull pawl. Use a screwdriver or
equivalent tool to pry the pull pawl at least 0.8 mm
(0.0313 in) to disengage the teeth from the actuator.
2. Use a wrench to turn the manual adjusting nut clockwise
until the brake shoes are fully retracted and the lining
clears the drum.
3. Remove both clevis pins and retainer clips or cotter pins.
4. Move the slack adjuster away from the clevis.
5. Discard the retainer clips and cotter pins and replace
them with new ones.
NOTE: Note the orientation of the slack adjuster with
reference to the push rod before removal to ensure
proper orientation at installation.
6. Remove the slack adjuster with a suitable puller.
Installation
1. Verify that the pushrod is fully retracted.
2. Install the inner washer on the camshaft. The inner
washer has a larger hole.
3. Apply Anti-Seize type lubricant to the camshaft splines.
Install the slack adjuster onto the camshaft with the
adjusting shaft hex pointing away from the air brake
CAUTION
You must disengage a pull pawl before rotating the
manual adjusting nut, or you will damage the pawl teeth.
CAUTION
When you remove a clevis pin that has a spring, hold the
spring with pliers. The spring can disengage from the
clevis with enough force to cause serious personal injury.
CAUTION
Always replace used clevis pin retainer clips with new
ones when you service an automatic slack adjuster. Do
not reuse retainer clips. When you remove a retainer clip,
it can bend out of shape and lose retention. Damage to
components can result.
CAUTION
Do not use a hammer to remove the slack adjuster.
Damage to the slack adjuster and/or camshaft splines
may result.
Reference Only
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