Audi A4 B6 Brake Booster Vacuum Pump Replacement (2002 After years of use, the rubber diaphragm inside the booster may leak or fail, causing the system to not work correctly. The Audi A4 also uses a power brake vacuum pump to assist in and maintain vacuum pressure in the booster. The booster, pump and lines can fail which usually results in having to push the pedal down harder when braking. Audi A4 B6 Brake Booster Replacement (2002-2008) | Pelican Replacing the brake booster on the Audi A4 is not difficult. It is just a tight fit, but it should take no more than five hours including bleeding the brakes. Note: you will need to remove the brake master cylinder with the brake booster, which means opening the brake lines.