Vacuum Brake Booster: Description and Operation

All vehicles use a 205 mm tandem diaphragm power brake vacuum booster. The vacuum booster though, may be unique for the type of brake system the vehicle is equipped with. For this reason, if the power brake vacuum booster requires replacement, be sure it is replaced with the correct part for the type of brake system that the vehicle is equipped with.

Vacuum Booster Identification:

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

NOTE: The 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 vacuum booster check valve is not repairable but can be replaced as a component of the vacuum booster.

The vacuum booster reduces the amount of force required by the driver to obtain the necessary hydraulic pressure to stop the vehicle.

The vacuum booster is vacuum operated. The vacuum is supplied from the intake manifold on the engine through the power brake booster check valve.

Vacuum Booster Assembly:

As the brake pedal is depressed, the vacuum booster's input rod moves forward. This opens and closes valves in the vacuum booster, allowing atmospheric pressure to enter on one side of a diaphragm. Engine vacuum is always present on the other side. This difference in pressure forces the output rod of the vacuum 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 systems and engine combinations require different vacuum hose routings.

The vacuum booster assembly mounts on the engine side of the dash panel. It is connected to the brake pedal by the input push rod. A vacuum line connects the vacuum booster to the intake manifold. The master cylinder is bolted to the front of the vacuum booster assembly.