Vacuum Booster

All vehicles use a 205 mm tandem vacuum booster. See Fig 2 . The purpose of vacuum booster is to reduce amount of force required to be applied to brake pedal by drivers foot, to obtain required hydraulic pressure in brake system to stop vehicle. The vacuum booster can be identified if required, by tag attached to body of vacuum booster. See Fig 3 . This tag contains following information. The production part number of vacuum booster, date it was built and who manufactured it.

NOTE: The vacuum 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 check valve used in vacuum booster is not repairable but can be replaced as a separate component of vacuum booster. See Fig 2 .

The vacuum booster is a vacuum operated devise. Vacuum is supplied from intake manifold on engine through check valve in vacuum booster. As brake pedal is depressed, vacuum booster input rod moves forward. This movement opens and closes valves in vacuum booster, creating a vacuum on one side of a diaphragm and allowing atmospheric pressure to enter on other. This difference in pressure forces output rod of vacuum booster out against primary piston of master cylinder. As pistons in master cylinder move forward this creates hydraulic pressure in brake system.

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

Fig 1: Master Cylinder (CutAway View)

Courtesy of CHRYSLER CORP.

Fig 2: Vacuum Booster (CutAway View)

Courtesy of CHRYSLER CORP.

Fig 3: Vacuum Booster Identification

Courtesy of CHRYSLER CORP.