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P A R T 2-1-GENERAL BRAKE SERVICE
2 - 3
DIAGNOSIS GUIDE—POWER BRAKES VACUUM BOOSTER—FRAME MOUNTED
BRAKE PEDAL KICKS
BACK W H E N APPLIED
R O U G H ENGINE IDLE
WITH BRAKES RELEASED
R O U G H ENGINE IDLE OR
STALL A N D HARD PEDAL
WITH BRAKES APPLIED
INTERMITTENT HARD
BRAKE PEDAL
HARD PEDAL—BOOSTER
DIAPHRAGM
RUPTURED
BRAKES D O NOT
RELEASE
This condition m a y be caused by
Replace the slave cylinder piston
a defective hydraulic piston check
and/or piston cup.
valve or slave cylinder piston cup.
Check for vacuum leaks in the
required. This condition m a y also
vacuum line, loose hose connections,
be caused by vacuum leaks at the
a loose body clamp, or a weak con-
control valve diaphragm, at the valve
trol
valve
piston
return
spring.
piston assembly, or at the power dia-
Check all connections and tighten
phragm. R e m o v e and overhaul the
them or replace damaged parts as
booster assembly.
Check the condition of the air
valve plate, or the control valve pis-
cleaner. If i t is clogged with dirt, re-
ton not seating properly on the plate
place the air cleaner felt. A sticking
m a y also cause this condition. In ad-
control valve piston, leaks at the
dition, the booster diaphragm m a y
control valve diaphragm or atmos-
be damaged. Remove and overhaul
pheric valve seal, dirt on the control
the booster assembly.
Check for an obstructed air clean-
draulic fluid. Clean or replace darn-
er, a defective vacuum check valve,
aged parts, refill the hydraulic sys-
or a slave cylinder piston sticking in
tem with n e w heavy-duty type brake
the bore due to dirt or inferior hy-
fluid,
and bleed the system.
W h e n
a ruptured diaphragm i s
premature failure.
found, check for gasoline odor on
Gasoline can get on the diaphragm
the diaphragm. Gasoline will deteri-
from the intake manifold if the vac-
orate the diaphragm and cause a
u u m check valve is defective.
Check the rear of the vacuum
control valve piston holds the brakes
chamber for damage. This condition
in an applied position, disconnect
m a y also be caused by a sticking
the booster vacuum line from the
control valve piston, a faulty slave
vacuum check valve and install a
cylinder piston check valve, dirty
pipe plug in the check valve open-
brake fluid, a sticking slave cylinder
ing. This permits the brakes to re-
piston, a sticking push rod, or a
lease. Manual application of brakes
faulty check valve in the end cap.
m a y then be made without assistance
Remove and overhaul the booster.
from the booster.
In case of emergency, if a sticking
DIAGNOSIS GUIDE—POWER BRAKES VACUUM BOOSTER—DASH MOUNTED
H A R D
P E D A L
Check as follows to see i f the
Brake pedal linkage sticking.
power unit is operating: With the en-
Faulty vacuum check valve.
gine
stopped, depress
the brake
Collapsed or leaking vacuum hose.
pedal several times to eliminate all
Plugged vacuum fittings
vacuum from the system. Apply the
Ud
^
Qg
v a c u u m
c h a m b e r
brakes, and while maintaining pres-
,
r
, .
,
,
,
, .
. , °
.
V a c u u m
check
valve stuck in
sure on the pedal, start the engine.
,
,
.,
. y
.
,
,
b
,
closed position.
If the unit is operating, the brake
, , - , , ,
pedal will move forward slightly
Leak ,n bellows assembly.
when engine vacuum power is added
Diaphragm assembly out of place
to the foot pressure on the pedal. If
ln
housing locating radii:
the unit i s not operating, there will
V a c u u m leak in automatic trans-
be no pedal action.
mission T.V. vacuum line connec-
If this check shows that the unit
tion or fitting.
is not operating, check for the fol-
V a c u u m leak in forward, vacuum
lowing:
housing.
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