Checking the brake booster (vacuum test) (Cooper)

Special tools required: 

• 34 3 100

Preliminary work needed: 

• If necessary, uncover brake booster
  • Detach the vacuum hose from the brake booster. Install the vacuum tester 34 3 100 between the brake booster and the vacuum hose of the check valve.
  • Start the engine.
  • Check the build-up of the vacuum.
  • Switch off engine.
  • Set a vacuum of no more than 0.8 bar by pressing the brake pedal and wait for the value to stabilize.
  • When the brake pedal is not depressed, the vacuum may drop by a maximum of 0.06 bar during a test period of 1 minute.

Courtesy of BMW OF NORTH AMERICA, INC.

If the required values are not achieved: 

• Replace the check valve
• Check the seal between the brake booster and the tandem brake master brake cylinder (sealing ring) for proper condition and correct sealing fit.
• If necessary, check the brake booster for leaks with a smoke tester
• If the setpoint values are not reached after another check, the brake booster must be replaced.