Vacuum Brake Booster: Description and Operation

All vehicles use a 230 mm single diaphragm power brake vacuum booster. There are however two different booster designs; one for vehicles equipped with ABS and one for vehicles without ABS. These two boosters differ at the interface to the master cylinder. If the power brake booster requires replacement be sure it is replaced with the correct part.

Power Brake Booster Identification:

The power brake booster can be identified 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, who manufactured it, and brake sales code.

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.

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

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.

Power Brake Booster Assembly:

As the brake pedal is depressed, the power booster input rod moves forward. This opens and closes valves in the power 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 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 options available for this vehicle require that different vacuum hose routings be used.

The power brake 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 power booster to the intake manifold. The master cylinder is bolted to the front of the power brake vacuum booster assembly.