34 00 017 Checking brake booster (low-pressure test)
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Necessary preliminary tasks:
- Remove LEFT MICROFILTER HOUSING
- Detach hose from connection piece. Install vacuum tester 34 3 100 between connection piece and vacuum hose of non-return valve.
- Start engine.
- Check buildup of partial vacuum.
- Switch off engine.
- Press the brake pedal to set a vacuum pressure of not more than 0.8 bar and wait for the value to stabilize.
- When the brake pedal is not pressed, the vacuum pressure is permitted to drop over a test period of 1 minute by max. 0.06 bar.
Fig 1: Installing Vacuum Tester (34 3 100) Between Connection Piece And Vacuum Hose Of Non-Return Valve
If specified values are not reached:
- 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.
- If the specified values are not achieved when the test is repeated, you must replace the brake booster.