Brake Booster
- Remove left microfilter for interior ventilation. See MICROFILTER HOUSING LOWER SECTION under REMOVAL & INSTALLATION.
- Detach hose from connection piece. Install Vacuum Tester (34 3 100) between connection piece and vacuum hose of non-return valve. See Fig 1.
- Start engine. Check buildup of partial vacuum.
- Switch off engine. Press brake pedal to set a vacuum pressure of not more than 12 psi (0.8 bar) and wait for the value to stabilize.
- Release the brake pedal. Vacuum pressure should not drop more than 9 psi (0.6 bar) over a period of one minute.
- If specifications are not reached, perform the following:
- Check line connections for vacuum seal.
- Replace non-return valve.
- Check seal between brake booster and brake master cylinder (sealing ring) for perfect condition and correct seating.
- Perform test again. If specifications are not reached, replace brake booster. See BRAKE BOOSTER under REMOVAL & INSTALLATION.
Courtesy of BMW OF NORTH AMERICA, INC.