Vacuum Brake Booster: Description and Operation

Power Brake Booster - Servo Unit

The servo unit provides controlled power assistance to to the brake pedal when pressure is applied. Vacuum is obtained from the intake manifold. The vacuum is applied to both sides of a flexing diaphragm and by admitting atmospheric pressure to the rear diaphragm, assistance is obtained. The servo unit is mounted between the brake pedal and master cylinder and is linked to these by push rods. Should a vacuum failure occur, the two push rods will act as a single rod allowing the brakes to function in the normal way, although more effort will be required to operate the brake pedal.