Section 12: BRAKE AND AIR SYSTEM
PA1562
17
perform this procedure before replacing the rotor
to ensure the cause of the problem is properly
solved.
1. Check for presence of residual pressure:
To check if there is any residual air pressure in
the brake chamber, make four or five brake
applications, then try to turn the wheel manually,
if the wheel does not turn, use a wrench to crack
the air line and listen for trapped air in the brake
chamber then try to turn the wheel manually
again. If you find trapped air in the brake
booster, ensure that all pneumatic components
in the braking system are functioning properly.
NOTE
A residual pressure of 2-3 PSI in the system is
sufficient to prevent the brakes from releasing.
Also the stop light switch can operate with as
little as 1 PSI, therefore an illuminated brake
light does not mean brakes are dragging.
2. Pad to rotor clearance inspection:
Remove clip and washer (26 & 45, Fig. 26),
push down retainer bar (11), pull out pin (44)
and remove retainer bar. Push caliper toward
actuator (center of vehicle) for maximum
clearance.
FIGURE 26: CLEARANCE INSPECTION 12119
3. Measure pad to rotor clearance:
Place a long feeler gauge (long enough to
measure across entire tappet surface) between
the tappet and the backing plate of the pad,
measure clearance at both tappets. Clearance
should range between 0.020 and 0.035 inch (0.5
mm and 0.9 mm), with a maximum difference
between tappet measurements on same brake
of 0.008 inch (0.2 mm).
FIGURE 27: RUNNING CLEARANCE 12116
4. Checking the adjuster
CAUTION
Use only a standard box wrench on the
adjuster hexagonal pinion. Do not overtorque
the pinion as overtorquing will damage the
pinion.
a) Remove cap (37, Fig. 27).
b) Using a box wrench (8 mm), turn the
adjuster pinion (23, Fig. 28) counterclock-
wise about 2 - 3 clicks to increase running
clearance. By operating the braking system
about 5 - 10 times (30 PSI or 2 bar), the
wrench should turn clockwise in small
increments if the adjuster is functioning
correctly (Figs. 28 and 29).
NOTE
With increasing number of applications, the
incremental adjustment will decrease.
c) In case of malfunction, i. e. the pinion or box
wrench:
i) Does not turn.
ii) Turns only with the first application.
iii) Turns forwards then backwards with
every application.
In any of the above cases, the automatic
adjuster has failed and the caliper must be
replaced. In such cases the brakes can be
adjusted manually to run a short distance.
d) Take the box wrench off. Replace the cap
and check for proper sealing.
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