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MAINTENANCE AND LUBRICATION
Replacing Slack Adjuster
The installation guide must be used when
installing or reinstalling automatic slack adjuster.
Failure to do so may result in improperly adjusted
brakes which may cause brake damage or lead to
brake failure.
1. Chock wheels to prevent vehicle from rolling.
Release spring and service brake. Air chamber push
rod must be fully released (See Figure 4-11).
2. To maintain a fully released parking brake, a
minimum of 105 psi reservoir pressure must be
maintained. If air pressure is not available the spring
brake must be manually caged.
3. Remove the existing slack adjuster and clevis - DO
NOT REMOVE EXISTING JAM NUT.
4. Install the new clevis (with 1/2" pin) onto the push rod
up to the jam nut - DO NOT TIGHTEN JAM NUT.
5. Fit the installation guide over the cam splines so the
1/2" pin slots face the air chamber.
6. Swing the guide into the clevis until the appropriate
slot totally engages 1/2" pin.
4-18
CAUTION
7. Observe the guide pointer arrow:
If the guide pointer is above the clevis pointer, adjust
clevis CCW for alignment.
If the guide pointer is below the clevis pointer, adjust
clevis CW for alignment.
8. Reposition clevis until the guide pointer aligns with
the clevis pointer.
9. Verify by engaging 1/4" pin through the clevis and
guide.
10. Tighten jam nut to 50 ft.-lbs. torque min.
11. Remove the guide from cam shaft.
12. If the push rod threads extend through the clevis
more than 1/16", remove clevis and cut rod to length.
13. If the push rod is not fully engaged in clevis body,
install a new push rod - cut to length.
14. Install the slack adjuster on the cam shaft.
15. Rotate the manual adjuster shaft CW until the slack
adjuster arm holes align with the clevis. Install 1/2"
and 1/4" pins and cotter pins.
Adjusting Slack Adjuster
1. Rotate the manual adjuster CW until brake shoes
contact drum.
2. Back off manual adjuster 1/2 turn. (CCW)
3. Manually uncage the spring brake.
4. Build up vehicle air pressure.
5. Fully apply and release the brakes several times to
check for adequate clearance to all adjacent
components.
6. Measure the distance from air chamber to 1/2" pin.
Apply brakes with 100-105 psi air pressure and
remeasure distance to 1/2" pins.
7. The stroke (difference of these two measurements)
must be less than 2 inches.
F-563-0610 Edition
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