Removal
Brake booster servo installation details
1. Remove the brake master cylinder (see section Disassembly and assembly of the main brake cylinder (MBC) of the "Tandem" type (models 140.028/032/033/135)).
2. Remove the ASR support pump.
3. Check the brake master cylinder for damage and leaks.
4. Unscrew or disconnect the vacuum tube (8) from the vacuum booster (16). Press the brake pedal several times to reduce the pressure in the vacuum booster.
5. Disconnect the connector (A7/7x1), (A7/7x2) from the BAS control unit or, on models with ESP, disconnect the connector from the solenoid valve switch and the BAS diaphragm displacement sensor on the vacuum booster. On models with BAS and ESP, the BAS control unit is integrated with the ESP control unit.
6. Remove the lower instrument panel cover.
7. Disconnect the brake pedal return spring.
8. Remove the retainer and pin (26).
9. Unscrew the nut (23) from the bracket (22).
10. Remove the vacuum booster (16).
11. Check the gasket (16).
Installation
Installation is carried out in the reverse order of removal.
Examination
1. Press the brake pedal to reduce the pressure in the vacuum booster.
2. Disconnect the tester from the vacuum booster. 3. Connect the pressure gauge (051) to the brake caliper with an adapter.
4. Connect the pedal force sensor (06) to the brake pedal.
5. Start the engine and build up a pressure of 0.75 - 0.80 bar by pressing and releasing the accelerator pedal. If the vacuum reached is significantly lower than required or the vacuum decreases immediately, the sealing ring between the vacuum booster and the master cylinder is damaged or the valve in the vacuum pipe needs to be checked.
6. Create the required force on the accelerator pedal and read the pressure in the line. The dependence of the pressure in the hydraulic drive on the force applied to the foot brake pedal is given in Specifications.