Located on the driver’s side of the car towards the back of the engine compartment, the vacuum-operated brake booster is the heart of a “power brake” system. The master cylinder mounts to the front of the brake booster.
The brake booster uses the differential of engine vacuum (negative pressure) and atmospheric pressure (positive pressure) to multiply force from the driver’s leg. This applies increased force to the pushrod of the master cylinder, generating more pressure from the master cylinder than from use of the driver’s leg alone.
Brake boosters are generally very reliable and require no maintenance. Some boosters have a small filter in the vacuum line supplying the booster. This filter should be replaced periodically to ensure a consistent flow of vacuum to the booster. It should be inspected regularly to make sure that its vacuum connection and hose are sound and that the connection grommet seals tightly around the vacuum connection. Symptoms of brake booster problems include excessive brake pedal effort, a rough running engine, excessive idle speed, or a whooshing or hissing noise. Have the symptom checked by a professional technician to pinpoint the cause.