How to Check a Brake Power Boosterby K.K. Lowell
A brake power booster is a vacuum operated device which reduces the effort needed to press the brake pedal and apply the brakes. In most cases the vacuum is created by the running engine and air is drawn from the booster through a rubber hose connected to the intake manifold. Diesel engines do not produce much vacuum and may employ a vacuum pump. High pedal effort and poor braking action indicate a problem with the booster or the vacuum system.
Depress the brake pedal repeatedly with the engine off.
Continue to hold the brake pedal down and start the engine. The brake pedal should be pulled down slightly after the engine starts. A problem with the brake booster or the vehicle vacuum system is indicated if the pedal does not pull down slightly.
Connect a vacuum gauge to the hose from the engine to the brake booster and start the engine. A reading of 16 inches or more of vacuum rules out a problem with the vacuum system and indicates the need to replace the brake booster.