Chevrolet Light Duty Truck 1973 Service Manual page 326

5 -6 0 BRAKES
General Description.......................................................................... 5-60
Theory of Operation......................................................................... 5-60
Maintenance and Adjustments...................................................... 5-66
Component Part Replacement....................................................... 5-66
Diagnosis............................................................................................... 5-67
The Power brake Unit is a self-contained hydraulic and
vacuum unit, utilizing manifold vacuum and atmospheric
pressure for its power.
This unit permits the use of a low brake pedal as well as
A power brake is used with the brake system to reduce
the braking effort required by the driver. A combined
vacuum and hydraulic unit, which utilizes engine
manifold vacuum and atmospheric pressure, is used to
provide power assisted application of vehicle brakes.
The unit is used in conjunction with a conventional
brake system. From the master cylinder connection
outward to the wheel units, there is no other change in
the brake system.
In addition to the master cylinder connections, the unit
requires a vacuum connection to the engine intake
manifold (through a vacuum check valve) and a
mechanical connection to the brake pedal. The unit is
self-contained.
POWER BRAKES
Inspection............................................................................................ 5-66
Lubrication.......................................................................................... 5-66
Bleeding............................................................................................... 5-66
Air Cleaner Service......................................................................... 5-66
Power Brake U nit............................................................................ 5-66
GENERAL DESCRIPTION
THEORY OF OPERATION
INDEX
less pedal effort than is required with the conventional
(nonpower) hydraulic brake system. The unit is mounted
on the engine side of the dash panel and directly
connected to the brake pedal.
The vacuum power unit contains the power piston
assembly, which houses the control valve and reaction
mechanism, and the power piston return spring. The
control valve is composed of the air valve (valve
plunger), the floating control valve assembly, and the
push rod. The reaction mechanism consists of a
hydraulic piston reaction plate and a series of levers. An
air filter, air silencer, and filter retainer are assembled
around the valve operating rod filling the cavity inside
the hub of the power piston. The push rod or valve
operating rod, which operates the air valve, projects out
of the end of the power unit housing through a rubber
dust guard. A vacuum check valve assembly is mounted
in the front housing assembly for connection to the
vacuum source.
LIGHT DUTY TRUCK SERVICE MANUAL