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7. If the brakes have been running tight, the
control arm location should be checked.
WARNING
IF THE ADJUSTER APPEARS NOT TO
BE OPERATING, CHECK THE OTHER
BRAKE COMPONENTS FOR PROPER
FUNCTION AND ELIMINATE ANY BIND-
ING. RECHECK THE AUTOMATIC
SLACK ADJUSTER. IF THE ADJUSTER
IS NOT FUNCTIONING, THE UNIT MUST
BE REPLACED BECAUSE FAILURE OF
PROPER ADJUSTMENT FUNCTION
WILL RESULT IN LOSS OF BRAKES.
b. Replacing Slack Adjuster (See Figure
4-11)
CAUTION
THE INSTALLATION GUIDE MUST BE
USED WHEN INSTALLING OR REIN-
STALLING AUTOMATIC SLACK AD-
JUSTER. FAILURE TO DO SO MAY RE-
SULT IN IMPROPERLY ADJUSTED
BRAKES WHICH MAY CAUSE BRAKE
DAMAGE OR LEAD TO BRAKE FAIL-
URE.
1. Chock wheels to prevent vehicle from
rolling. Release spring and service brake.
Air chamber push rod must be fully
released.
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.
4-18
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.
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.
c. 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.
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