Ford Focus Service Manual: Brake Booster - Description and Operation

The brake booster consists of:

• brake booster assembly
• brake booster vacuum hose
• brake booster vacuum check valve

The brake booster is a single-diaphragm type which utilizes engine vacuum to reduce brake pedal effort and travel. The brake booster is divided into separate vacuum and atmospheric chambers by the diaphragms. Engine vacuum is supplied to the brake booster through the brake booster hose and a one-way check valve. The check valve retains the engine vacuum in the brake booster and allows for several power-assisted brake applications with the engine off.

When the brake pedal is applied, vacuum replaces the atmospheric pressure in the brake booster, reducing the effort required at the brake pedal to slow the vehicle. When the brake pedal is released, vacuum returns to the brake booster through the brake booster vacuum hose and check valve.