Jeep 1987 Wrangler Workshop Manual page 981

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BRAKE SYSTEM
DIAGNOSIS
6.
HARD
BRAKE PEDAL -
( c o n t ' d . )
POSSIBLE CAUSES
(5) Caliper, wheel cylinder, or master
cylinder pistons sticking or seized.
(6) Booster vacuum check valve malfunction.
(7) Power brake booster has internal bind.
(8) Master cylinder inlet ports blocked by
dirt, scale, rust, or have small burrs
(blocked ports prevent fluid return to
reservoirs.)
(9) Brake hoses, tubes, fittings clogged or
restricted.
(10) Brake fluid contaminated with improper
fluids (motor oil, transmission fluid,
causing rubber components to swell
and stick in bores.
(11) Low engine vacuum.
CORRECTION
(5) Repair or replace as necessary.
(6) Test valve as follows:
(a) Start engine, increase engine speed
to 1500 rpm, close throttle and
immediately stop engine.
(b) Wait at least 90 seconds then
depress brake pedal.
(c) If brakes are not vacuum assisted for
2 or more applications, check valve
is faulty.
(7) Test unit as follows:
(a) With engine stopped, apply bcakes
several times to exhaust all vacuum
in system.
(b) Shift transmission into neutral,
depress brake pedal and start
engine.
(c) If pedal height decreases with foot
pressure and less pressure is
required to hold pedal in applied
position, booster vacuum system is
operatihg normally. Test booster as
outlined in item E, Decreasing Brake
Pedal Travel. If booster exhibits a
bind condition, replace the unit.
(8) Repair or replace master cylinder.
CAUTION: Do not attempt to clean
blocked ports with wire, pencils, or
similar implements. Use compressed air
only.
(9) Use compressed air to check or unclog
parts. Replace any damaged parts.
(10) Replace all rubber components,
combination valve and hoses. Flush
entire brake system with DOT 3 brake
fluid or equivalent.
(11) Adjust or repair engine.
H. GRABBING BRAKES
POSSIBLE CAUSES
(1) Brakelining or pads contaminated by
grease or brake fluid.
(2) Parking brake cables incorrectly
adjusted or seized.
(3) Incorrect pads or brakelining or lining
loose on brakeshoes.
(4) Caliper anchor plate bolts loose.
CORRECTION
(1) Determine and correct cause of
contamination and replace brakeshoes
in axle sets.
(2) Adjust cables. Replace seized cables.
(3) Replace pads or lining in axle sets.
SEE
I.S.
N
O
T
E
S
(4) Tighten bolts.
K-9