Vacuum Brake Booster: Testing and Inspection

Check Brake Booster

Modification Notes:

Inspect
1 Operate brake pedal several times until vacuum in brake booster (16) is reduced
2 Connect tester (030) at brake booster

NOTE: Measurement connection (031) for checking the check valve (17) or brake booster (16).

3 Connect pressure tester (051) with connection fitting to brake caliper

NOTE: After testing, only bleed the brake caliper to which the pressure tester was connected.

4 Connect pedal force measuring instrument (060) at brake pedal
5 Start engine and create a vacuum of 0.75 to 0.80 bar by accelerating and then suddenly releasing the accelerator pedal

NOTE:
- If the vacuum is considerably lower or if the vacuum drops immediately, the O-ring between the brake booster and master brake cylinder may be damaged or the non-return valve in the vacuum line may be defective, checking non-return valve
- Remove/Install master brake cylinder, replace O-ring

6 Apply specified force to brake pedal and read off line pressure.
- To cover measurement errors as far as possible (wrong force on brake pedal, wrong vacuum) and measurement scatter of the gauges, a tolerance of ±10 bar on the specified value is permissible.

NOTE: The measured value must be within the value range.

7 Disconnect tester (030) at brake booster
8 Disconnect pressure tester (051) with connection fitting from brake caliper
9 Remove pedal force measuring instrument (060) at brake pedal
10 Bleed brake system.