Vacuum Boosters - GMC G Service Manual

A. Input Rod Seal
B. Power Piston Seal
C. Housing Seal
D. Spool Valve Plug Seal
E. Accumulator Seal
F. Return Port Fitting
Figure 1 — Hydro-Boost Seal Leak Diagnosis
DESCRIPTION
SINGLE DIAPHRAGM MODEL
This booster is a single-diaphragm, vacuum-suspended
unit. It may have a single-function vacuum switch to acti­
vate the brake warning light in case of low booster vacuum
or vacuum pump malfunction. In a normal operating mode,
with the service brakes in the released position, a vacuum-
suspended booster operates with vacuum on both sides of
its diaphragm. When the brakes are applied, air at atmo­
spheric pressure is admitted to one side of the diaphragm
to provide the power assist.
TANDEM DIAPHRAGM MODEL
This booster is a tandem-diaphragm, vacuum-sus­
pended unit. It may have a single dual-function vacuum
switch to activate the brake warning light in case of low
booster vacuum or vacuum pump malfunction. In a normal
operating mode, with the service brakes in the released
position, a tandem-diaphragm, vacuum-suspended booster
operates with vacuum on both sides of its diaphragms.
When the brakes are applied, air at atmospheric pressure is
admitted to one side of each diaphragm to provide the
power assist.
HYDRAULIC BRAKE BOOSTER SYSTEMS 5A1-3
B-07849

VACUUM BOOSTERS

D. SPOOL VALVE PLUG SEAL. Damage to this seal
will be noticed by fluid leaking out past the plug. The
booster need not be removed from the vehicle for
seal replacement.
E. ACCUMULATOR SEAL. Damage to this seal will
result in fluid leakage past the accumulator cap. The
seal can be replaced while the booster is installed on
the vehicle.
F. RETURN PORT FITTING. Tighten the fitting to 10
N«m (7 ft. lbs.). If the leak continues, replace the seal
ring under the fitting.
VACUUM BOOSTER
REPLACEMENT
H Remove or Disconnect (Figure 2)
• Apply the parking brake.
1. Mounting nuts (1).
2. Master cylinder (2).
• Support the master cylinder.
3. Vacuum hose from the check valve.
4. Booster pushrod (5). Refer to HYDRAULIC BRAKES
(SEC. 5A).
5. Booster mounting nuts (4).
• The mounting nuts must be removed from
inside the vehicle.
6. Vacuum booster (3).