Vacuum Brake Booster: Description and Operation

The purpose of the vacuum operated power brake booster is to reduce the amount of force applied to the brake pedal by the drivers foot. To obtain the required hydraulic pressure in the brake system to stop the vehicle.
This vehicle utilizes a Bosch vacuum booster for all applications.

Power Brake Booster Identification:

The power brake booster can be identified if required, by the tag attached to the body of the booster assembly. This tag contains the following information. The production part number of the power booster assembly, the date it was built and who manufactured it.

NOTE: The power brake booster assembly is not a repairable part and must be replaced as a complete unit if it is found to be faulty in any way. The power booster vacuum check valve is not repairable but can be replaced as an assembly.

Power Brake Booster Assembly:

The power brake booster is vacuum operated. The vacuum is supplied from the intake manifold on the engine through the power brake booster check valve.
As the brake pedal is depressed, the power boosters input rod moves forward. This opens and closes valves in the power booster, creating a vacuum on one side of a diaphragm and allowing atmospheric pressure to enter on the other. This difference in pressure forces the output rod of the power booster out against the primary piston of the master cylinder. As the pistons in the master cylinder move forward this creates the hydraulic pressure in the brake system.
Different engine combinations require different vacuum hose routines.
The power brake booster assembly mounts on the engine side of the dash panel. It is externally connected to the brake system by an input push rod to the brake pedal. A vacuum line connects the power booster to the intake manifold. The master cylinder is bolted to the front of the power brake booster assembly.