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Low Pressure Test

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  1. Remove heater bulkhead. See HEATER BULKHEAD .
  2. Pull hose off connection. Install vacuum tester 34 3 100 between connection and vacuum hose on non-return valve. See Fig 1.
  3. Start engine and check buildup of partial vacuum. Stop engine.
  4. Press brake pedal to set a partial vacuum of no more than 11.6 PSI (.8 bar) and wait for value to stabilize.
  5. When the brake pedal is not pressed, the partial vacuum is allowed to drop by maximum .8 PSI (.06 bar) over a test period of 1 minute.

If specified values are not reached:

  1. Check line connections for vacuum seal.
  2. Replace vacuum non-return valve.
  3. Check seal between brake booster and brake master cylinder (sealing ring) for perfect condition and correct seating.
  4. If the specified values are not achieved when the test is repeated, you must replace the brake booster.
  5. After removing tester, reinstall heater bulkhead. See HEATER BULKHEAD .
Fig 1: Installing Vacuum Tester
G00103324Courtesy of BMW OF NORTH AMERICA, INC.