Vacuum Assist Brake Booster Test
Vacuum brake boosters are common and found in most of today’s vehicles. They require a vacuum source and a tight seal to operate properly. If the vehicle has a hard brake pedal or if the booster is suspected to be faulty, test the booster before replacing it. The testing procedures for vacuum brake boosters are fairly straightforward.
Begin the test by pumping the pedal with the engine off to deplete the brake booster of any residual vacuum. Keep your foot on the brake pedal and start the engine. The brake pedal should move towards the floor, usually about ¼ inch or so. If there is no movement and the brake pedal remains firm, suspect a problem with the brake booster or its vacuum source.
To check the booster’s diaphragm some manufacturers recommend running the engine until it reaches operating temperature and holding your foot on the brake pedal while turning the engine off. The pedal should hold pressure for a specified period of time, usually around 30 seconds or so.