Chevrolet 1980 Light Duty Truck Service Manual page 357

may cause the leak. If scratches are present, housing cover
must be replaced. If no excessive scratches are present, then
the booster seal kit can be used to replace the appropriate
seals.
2. POWER PISTON SEAL: Power piston seal
damage will be noticed by fluid leaking out at the common
master cylinder-brake booster vent and possible reduction
in power assist. The booster must be removed from the
vehicle and disassembled. The piston should be checked for
any scratches that may be the cause of the leak. If scratches
are present, then the input rod and power piston assembly
must be replaced. If no excessive scratches are present, then
the booster seal kit can be used to replace the appropriate
seals.
3. HOUSING SEAL: If the housing seal is damaged,
fluid will leak out from between the two housings. The
booster must be removed from the vehicle and disassembled.
The booster seal kit should be used to replace the housing
and input rod and power piston seals.
4. SPOOL VALVE PLUG "O" RING SEAL:
Damage to this seal will be noticed by fluid leaking out past
the plug. The booster need not be removed from the vehicle.
The master cylinder should be disconnected from the
booster.
Press in on spool plug, insert a small screwdriver
between snap ring and housing bore. This unseats one side
of the spool plug snap ring from its groove in the bore. Then
remove the snap ring from the bore.
5. ACCUMULATOR
this seal will result in fluid leakage past the accumulator
cap. The seal can be replaced while the booster is installed
on the vehicle. A catch basin should be placed under the
booster to catch the fluid when the accumulator or spring
cap is removed.
CAUTIO N: Before removing the cap, the
brake pedal must be pumped 4-5 times to
deplete accumulator pressure. Refer to
Fig. 5-1--Seal Leakage Diagnosis
RING SEAL: Damage to
"O"
HYDRO— BOOST SEAL LEAKAGE
A . IN P U T SEAL LEAK — F lu id le a k a g e fro m housing
cover en d o f b o o s ter n e a r re a c tio n b o re . R ep lace
seal(s).
B. P IS T O N SEAL LEAK — F lu id le a k a g e fro m ve n t a t
fr o n t o f u n it n e a r m aster c y lin d e r. R e p la c e s e a l.
C. H O U S IN G — F lu id le a k a g e b e tw e e n th e housing
a n d housing cover. R e p la c e s e a l.
D. S P O O L VALVE SEAL — F lu id le a k a g e n e a r p lu g
a r e a . R e p la c e s e a l.
E. A C C U M U L A T O R C A P SEAL — F lu id le a k a g e from
a c c u m u la to r a r e a . R e p la c e s e a l.
F. RETURN PORT F IT T IN G SEAL —
"Pneumatic Accumulator
Service Procedure".
6. EXTERNAL LEAKAGE AT THE RETURN
PORT FITTING: Tighten fitting to 7 lb. ft. (10 N-m). If
it continues to leak, replace
7. EXTERNAL LEAKAGE
PRESSURE GEAR OR PUMP: Torque tube nut to 30 lb.
ft. (40 N *m). If it continues to leak, check for damaged tube
flares; if OK, replace tube seats.
TROUBLE SHO O TING AND TESTING (Fig. 5-2)
The Hydro-Boost differs from vacuum brake boosters
not only in the source of power (hydraulic versus vacuum)
but in the fact that it is also a part of another major sub­
system of the vehicle-the power steering system. Therefore,
problems or malfunctions in the steering system may affect
the operation of the booster, just as a problem in the booster
may affect the steering system. The following noises are
associated with the Hydro-boost system and may or may
not be cause for customer complaint. Some are normal and
for the most part temporary in nature. Others may be a sign
of excessive wear or the presence of air in either the booster
or the steering system.
1. Moan or low frequency hum usually accompanied
by a vibration in the pedal and/or steering column may be
observed during parking maneuvers or other very low speed
maneuvers. This may be caused by a low fluid level in the
power steering pump or by air in the power steering fluid
due to holding the pump at relief pressure (steering wheel
held all the way in one direction) for an excessive amount
of time (more than 5 seconds). Check the fluid level and fill
to mark. System must sit for 1 hour to remove the air. If
the condition persists, this may be a sign of excessive pump
wear and the pump should be checked; Refer to Section 3B.
2. At or near power runout, (brake pedal near fully
depressed position) a high speed fluid noise (faucet type)
may be heard. This is a normal condition and will not be
heard except in emergency braking conditions, or with
BRAKES 5-3
R e p la c e s e a l.
On-Vehicle
ring under fitting.
"O"
AT THE HIGH
LIG H T T R U C K S ER V ICE M AN UAL