Checking the condition, removing and installing the brake booster (BMW 5 Series E28)

Components of a typical vacuum booster pushrod assembly

Checking the work

1. With the engine off, press the brake pedal several times until its travel stabilizes.

2. Press the pedal and hold it, then start the engine. If the pedal drops slightly, then everything is fine.

Checking for leaks

1. Start the engine and turn it off after one or two minutes. Slowly press the brake pedal several times. If the pedal goes far down the first time, and then gradually rises on the second and third press, then the vacuum booster is sealed.

2. Press the brake pedal while the engine is running, then stop the engine without releasing the pedal. If the pedal travel does not change after holding it down for 30 seconds, the vacuum booster is sealed.

Removal and installation

1. Removing the vacuum booster requires special tools and cannot be done by a home mechanic. If the problem continues to bother you, it is recommended to replace the unit completely.

2. Remove the master cylinder as described in Section Removal and installation the master brake cylinder.



3. Disconnect the vacuum hose from the brake booster.

4. Working in the passenger compartment, remove the storage compartment and lower the trim panels on the left side.



5. Remove the clamp and fork pin to disconnect the pushrod from the cross shaft arm (for right-hand drive models) or brake pedals (for left-hand drive models). On left-hand drive models, also disconnect the brake pedal return spring.



6. Loosen the four mounting nuts and remove the vacuum booster unit from the engine compartment.

7. Inspect the small filter inside the protective boot on the tappet. If it is clogged, it may affect the operation of the vacuum booster. To clean the filter, wash it in a mild soap solution. If it still does not clean, replace it.



8. Installation is the reverse of the removal procedure. Tighten the brake booster mounting nuts to the required torque. Before installing the protective cover on the booster pushrod air filter, make sure that the notches on the filter are positioned at 180 degrees to the notches on the shock absorber.

On right-hand drive models, the brake pedal is on the right side of the car and is connected to the left side by a cross shaft. Adjustment is made on the pushrod on the left side, but the specified size is measured on the pedal on the right side.

9. Adjust the height of the brake pedal and the brake light switch (see section Adjusting the brake pedal).

10. Install the master cylinder (see section Removal and installation the master brake cylinder) and connect the vacuum pump.

11. Check the brakes thoroughly before starting normal operation of the vehicle.