Vacuum Brake Booster: Description and Operation

Brake Booster and Master Cylinder Assembly Overview

• Use only new brake fluid. Observe the information on the brake fluid reservoir!





1 Pedal Assembly Mounting Bracket

2 Self Locking Nut

• Always replace after removal

• 25 Nm

3 Brake Pedal

4 Gasket

• For the brake booster.

5 Brake Booster

• Including the brake pressure release solenoid (F84) and brake pressure magnetic coil (N247) (not interchangeable).

• On gas engines, vacuum is supplied from the intake manifold.

• Vehicles with gas engines and automatic transmissions are equipped with a brake system vacuum pump.

• On diesel engines, a vacuum pump is installed for vacuum creation.

• Function test:

- With the engine turned off, press the brake pedal firmly several times (to exhaust the vacuum in the unit).

- Press and hold the brake pedal with average foot pressure and start the engine. If the brake booster is working properly, the pedal will be felt to give noticeably under foot (booster assistance becomes effective).

• Replace as a unit in the event of malfunction (previously, check all vacuum lines).

• Removing and installing, refer to => [ Brake Booster ] Brake Booster.

6 Seal

7 Brake Booster Membrane Position Sensor (G420)

• Removing and installing, refer to => [ Brake Booster Membrane Position Sensor ] Service and Repair.

• Discontinued from 27.11.06.

8 Snap Ring

9 Seal

10 Self Locking Nut

• Always replace after removal

• 25 Nm

11 Brake Line, 14 Nm

• Master cylinder/primary piston circuit to hydraulic control unit.

• Identification at hydraulic unit - DK -.

12 Brake Line, 14 Nm

• Master cylinder/secondary piston circuit to hydraulic unit.

• Identification at hydraulic unit - SK -.

13 Brake Pressure Sensor (G201)

• Removing and installing, refer to => [ Brake Pressure Sensor 1 ] Service and Repair.

• In the Electronic Stabilization Program (ESP) unit from 27.11.06

14 Bracket

15 Brake Line

• To the left front brake caliper.

16 Master Cylinder

• Cannot be serviced. Replace as a complete unit if malfunctioning.

• Removing and installing, refer to => [ Brake Master Cylinder ] Service and Repair.

17 Sealing Plugs

• Lubricate with brake fluid and press into the brake fluid reservoir.

18 Brake Fluid Reservoir

19 Cap

20 Vacuum Hose

• Inserts into the brake booster.

21 Sealing Plugs

• Connection for the vacuum hose.