Pontiac FIREBIRD 1972 Service Manual page 450

SINGLE DIAPHRAGM POWER BRAKE-BENDIX 5B-3
GENERAL DESCRIPTION
The single diaphragm power brake
-
Bendix is used on
some X Series models. It can be identified by the black
color of the power unit, and master cylinder cover. Al-
ways make sure that the correct master cylinder is used
whenever replacement is necessary.
The power brake unit is a combined vacuum and hydrau-
lic unit for power braking. It consists of a power unit and
a dual-system master cylinder. This brake assembly has an
over-all ratio of 2.9 to 1 (2.9" of pedal travel moves the
power piston 1 "). The wheel brakes are the same, manual
or power.
Pedal travel and pressure compared to the conventional
braking system are greatly reduced. The brake pedal
height is approximately 1" above the accelerator pedal,
permitting the driver to shift his toe from the one pedal
to the other without lifting his heel from the floor.
The power brake unit utilizes engine intake manifold
vacuum and atmospheric pressure in its operation. These
units are self contained, requiring no additional external
rods or levers. The external vacuum line connection of this
unit is to the carburetor.
A vacuum check valve is connected in the vacuum line at
the front housing to prevent loss of vacuum when mani-
fold vacuum falls below that in the power brake system.
In case of engine failure and consequent loss of engine
vacuum, several applications of the brakes are possible by
using vacuum retained in the power unit. In case of com-
plete vacuum loss, brakes can be applied in the conven-
tional manner, although considerable effort is required
due to loss of power assist.
DESIGN
The vacuum power cylinder contains a power diaphragm
REAR HOUSING
DIAPHRAGM PLATE
VACUUM PORT
REACTION
DISC
PISTON STOP SCREW
REAR PI STON
"SPLASH" SEAL
FRONT VACUUM SEAL
DIAPHRAGM RETURN SPRING
CONSTANT VACUUM CHAMBER
CONTROL VACUUM CHAMBER
Fig. 5 8 - 1 Bendix Power Brake Cross Section