BMW Coupes and Sedans 1970-1988 Repair Guide

Hydraulically Operated Power Brake Booster



5, 6 and 7 Series Models

See Figure 1

Models equipped with anti-lock brakes require expensive and specialized equipment to bleed the brake system. If you do not own or have access to this equipment, it is best to have a properly equipped professional perform this procedure.

Exercise extreme care in handling brake fluid near the painted surface of vehicle as fluid will destroy the pain finish if allowed to come into contact with it.

  1. Release the pressure in the hydraulic accumulator by operating the brake pedal (with the engine turned OFF ) 20 times.
  3. Remove as much brake fluid as possible from the reservoir with a clean turkey baster or other equivalent tool.

When removing brake fluid, always replace with new DOT 3 or 4 grade brake fluid

  1. Disconnect the power booster apply-rod at the brake pedal. This is done by pulling off the bayonet clip and then pulling the pin out of the piston rod.

When removing or installing brake line or hoses, always use a backup wrench on the fitting to prevent twisting. Avoid bending the lines or damaging the coating.

Click image to see an enlarged view

Fig. Fig. 1: Brake pedal adjustment-7 Series models

  1. Unfasten the electrical connector and pull off the reservoir.
  3. Disconnect the brake hydraulic lines at the master cylinder.
  5. Unfasten the hydraulic hoses at the brake booster.
  7. Remove the bolts from the driver's side of the pedal base assembly and slide the booster and master cylinder assembly out. To separate the master cylinder and booster, remove the two bolts.
  9. Measure the distance from the end of the threads on the piston rod to the outer end of the forked fitting for the clevis pin. Then, transfer the fitting over to the new booster, turning it in a clockwise direction until the dimensions are the same.

To install:
  1. Attach the master cylinder to the booster tightening the retaining hardware to 18-21 ft. lbs. (25-29 Nm).
  3. Install the booster in position securing the booster with the attaching nuts tightened to 16 ft. lbs. (22 Nm). It is helpful to keep the following points in mind:
    1. When reattaching the hydraulic fittings to the booster, make sure everything is clean and use the special tools to tighten the fittings.
    3. Check the rubber seals for the master cylinder reservoir and replace them is necessary.
    5. Bleed the brakes. Test operation and boost of the system before driving the vehicle.