Pontiac FIREBIRD 1972 Service Manual page 439

SINGLE DIAPHRAGM POWER BRAKE-MORAINE 5A-3
RESERVOIR COVER FRONT SHELL
PRIMARY PISTON ASSEMBLY
Fig. 5A-1 Delco Moraine Power Brake
pedal down to the approximate height of the accelerator.
A reserve vacuum supply and the vacuum check valve
permit several applications of the power brake with
vacuum assist after the engine has stopped. After the
vacuum stored in the unit has been lost, or in case of
vacuum failure the brakes can be applied in the conven-
tional manner, although considerable effort will be re-
quired due to the loss of the power assist.
DESIGN
The unit is composed of two main sections: the vacuum
power cylinder and the hydraulic dual master cylinder.
The vacuum power cylinder contains the power piston
assembly which in turn houses the control valve, reaction
mechanism, and the power piston return spring. The con-
trol valve is composed of the air valve and the floating
control valve assembly. This valve is controlled by the
valve operating rod that projects through the end of the
power cylinder housing.
The reaction mechanism consists of a hydraulic piston
reaction plate and a series of levers. An air filter element,
protected by a rubber boot, is assembled around the valve
operating rod and fills the cavity inside the hub of the
power piston. The push rod, which operates the air valve,
projects out of the end of the power cylinder housing
through the boot. A vacuum check valve assembly is
mounted in the front housing assembly for connection to
the vacuum source.
Fluid reservoirs are integrally cast with the master cylin-
der and supply fluid to the spaces between the primary
and secondary seals through holes in the casting. Two
hydraulic outlets connect independently to the front and
rear wheel cylinders.
PRINCIPLES OF OPERATION
Principles of operation are basically the same as for the
Delco Moraine tandem power brake (Section SD), except
that the tandem unit has two diaphragms for added assist
in heavy duty applications.
A simplified explanation of basic power brake theory is
shown in Fig. 5A-3.