Vacuum booster — checking, removal and installation (BMW 3 Series E46)

Note: On models with ABS and Traction Control (ASC+T) or Dynamic Stability Control (DSC), removing the booster requires removing the ABS/ASC+T and/or DSC control unit. Since special equipment is required to remove these units, this work should be performed at a specialist workshop.

Examination

1. To check the operation of the booster, press the foot brake pedal several times to use up the remaining vacuum in the booster. Then start the engine, holding the pedal down. When starting the engine, you will feel the pedal "pull back" as the vacuum increases. After the engine has been running for some time, (at least a couple of minutes), muffle it. Now press the pedal. You should feel a normal force, and with subsequent presses the pedal should become "harder", and its stroke should decrease with each press.

2. If the amplifier does not work as described above, then first of all you need to check the amplifier valve (see paragraph 13).

3. If after checking the valve the amplifier continues to work unsatisfactorily, it is faulty. Replace the amplifier - it is impossible to repair.

Removal

Note: You will need new booster mounting nuts during installation.

4. Remove the master cylinder (see paragraph 10).

5. Disconnect the vacuum hose from the booster valve.

6. Remove the screws and remove the lower trim panel on the driver's side.

7. Unhook the spring, then remove the retainer and pin connecting the brake pedal to the booster pushrod (see paragraph 11, fig. 11.4).

8. Unscrew the amplifier mounting nuts. Then remove the amplifier from the engine compartment and remove it from the car (Fig. 12.8).

Installation

9. Installation is performed in the reverse order of removal. When installing, pay attention to the following.

• a) Check the condition of the booster valve sealing bushing and, if necessary, replace it.
• b) Before installing the new amplifier, remove the sound insulation from the old amplifier and attach it to the new amplifier.
• c) Make sure that the booster pushrod is correctly positioned relative to the brake pedal. Then secure the booster with the nuts and tighten them to the specified torque.
• d) Lubricate the booster pushrod axle with grease, insert the axle into place and secure it with the spring clip.
• d) Install the master cylinder (paragraph 10).
• e) Finally, start the engine and check for air leaks from the vacuum booster connections. Check the operation of the brake system before driving.