Pontiac FIREBIRD 1972 Service Manual page 464

5C-4 1972 PONTIAC SERVICE MANUAL
FRONT SHELL
- \
REAR DIAPHRAGM SPRING RETAINER
\
\
RUBBER GROMMET _ r
POWER DIAPHRA
RETURN SPRlN
PUSH ROD
FRONT SEAL
FRONT PLATE'
FRONT DIAPHRAGM
CENTER PLATE
2
a
,
REAR DIAPHRAGM
REAR PLATE
REAR SHELL
POPPET RETAINER
PPET
/
v
A , V F R F T l l R M
/
-
AIR FILTERS
VALVE ROD
\
DUST GUARD
VALVE PLUNGER
\ \
VALVE PLUNGER SPRING
\
SQUARE RING SEAL
REACTION DISC
Fig. 5C-2 Bendix Tandem Diaphragm Power Brake
rhree basic elements are combined into a single unit (Figs.
5C-1 and 5C-2).
These three basic elements are:
1. A vacuum power chamber which consists of a front
and a rear shell, a center plate, a front and a rear
diaphragm and plate assembly, a hydraulic push rod
and a vacuum diaphragm and plate return spring.
NOTE:
BOTH HYDRA ULIC PISTONS
MUSTRETURN FAR ENOUGH TO OPEN
BOTH COMPENSA TING POR TS, BUT
THE HYDRAULIC PUSH ROD SHOULD
AL WA YS REMAIN IN CONTACT WITH
THE REAR PISTON.
2. A mechanically actuated control valve integral with
the vacuum power diaphragms that controls the de-
gree of power brake application or release in accord-
ance with the foot pressure applied to the valve
operating rod through the brake pedal linkage. The
control valve consists of a single poppet with an at-
mospheric port and a vacuum port. The vacuum port
seat is a part of the valve body attached to the dia-
phragm assembly. The atmospheric port seat is a part
of the valve plunger which moves within the valve
housing hub of the diaphragm plates.
3. A hydraulic dual-system master cylinder with two
hydraulic fluid reservoirs, cast integrally with, and
connected to, the bore through separate sets of com-
pensating and fluid inlet (bypass) ports. Both reser-
voirs are sealed by a rubber diaphragm inside the
bale-type cover. A primary piston (rear) assembly
with secondary seal, primary cup, protector, spring,
screw and spacer; a secondary piston (front) assembly
with two back-to-back secondary seals, primary cup,
protector, spring and spring retainer; a piston stop
screw and O-ring seal are the operating components
of the two separate hydraulic systems.
The vacuum power diaphragms and parts that make up
the valve assembly are connected to the brake pedal
through the valve operating rod and pedal linkage. The
valve operating rod is connected to the valve plunger
which moves within the hub of the power diaphragm