Jeep 1987 Wrangler Workshop Manual page 980

BRAKE SYSTEM
DIAGNOSIS
E. DECREASING BRAKE PEDAL TRAVEL — (Pedal travel required for braking action decreases
and may result in hard pedal.)
POSSIBLE CAUSES
(1) Caliper or wheel cylinder pistons sticking
or seized.
(2) Master cylinder inlet ports blocked
(preventing fluid return to reservoirs) or
pistons sticking or seized in master
cylinder bore.
(3) Power brake unit malfunction.
CORRECTION
(1) Repair or replace the calipers, or wheel
cylinders.
(2) Repair or replace the master cylinder.
(3) Test unit as follows:
(a) Shift transmission into neutral and
start engine.
(b) Increase engine speed to 1500 rpm,
close throttle and fully depress brake
pedal.
(c) Slowly release brake pedal and stop
engine.
(d) Have helper remove vacuum check
valve and hose from booster. Check
for rearward movement of brake
pedal.
(e) If the pedal moves rearward, booster
has malfunctioned — replace booster.
1 0 1 3 4 2 E
F. SPONGY BRAKE PEDAL — (Pedal has soft, springy, spongy feel when pressed.)
POSSIBLE CAUSES CORRECTION
(1) Air in hydraulic system. (1) Bleed brakes
(2) Rear brakeshoes bent or distorted. (2) Replace brakeshoes.
(3) Rear drum brakes not properly adjusted. (3) Adjust rear brakes.
(4) Rear drums worn beyond specification. (4) Replace drums.
G. HARD BRAKE PEDAL - (Excessive pedal pressure required to stop vehicle. May be
accompanied by brake fade.)
POSSIBLE CAUSES
(1) Loose or leaking booster vacuum hose.
(2) Incorrect or poor quality brakelining.
(3) Bent, broken, distorted brakeshoes.
(4) Calipers binding or dragging on
mounting pins. Rear brakeshoes
dragging on support plate.
CORRECTION
(1) Tighten connections or replace leaking
hose.
(2) Replace lining.
(3) Replace brakeshoes.
(4) Replace mounting pins and bushings.
Clean rust or burrs from rear brake
support plate ledges and lubricate ledges
with molydisulfide grease.
NOTE: If ledges are deeply grooved or
scored, do not attempt to sand or grind
them smooth — replace support plate.
1 0 1 3 4 2 G
K-8