BMW Coupes and Sedans 1970-1988 Repair Guide

Vacuum Operated Power Brake Booster

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REMOVAL & INSTALLATION



3 Series
EXCEPT 320i

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.


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

  1. Disconnect the negative battery cable.
  2.  

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.

  1. Draw off brake fluid in the reservoir and discard.
  2.  

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

  1. Remove the reservoir, then disconnect and cap the clutch hydraulic hose.
  2.  
  3. Tag for identification, then disconnect all brake lines from the master cylinder.
  4.  
  5. Unfasten the retaining hardware securing the master cylinder to the booster, and remove the master cylinder from the vehicle.
  6.  
  7. Remove the lower instrument panel trim from the driver's side of the passenger compartment.
  8.  
  9. Remove the return spring from the brake pedal. Press off the clip and remove the pin which connects the booster rod to the brake pedal.
  10.  
  11. Remove the four nuts securing the booster, and pull the booster and master cylinder out of the engine compartment.
  12.  
  13. If the filter in the brake booster is clogged, it will have to be cleaned. To do this, remove the dust boot, retainer, damper, and filter, then clean the damper and filter. Make sure when reinstalling that the slots in the damper and filter are offset 180°.
  14.  

To install:
  1. Install the booster and master cylinder back into position. Tighten the retaining nuts to 16 ft. lbs. (22 Nm).
  2.  
  3. Connect the booster rod to the brake pedal using the clip removed earlier. Do not forget to install the spring. Adjust the stoplight switch for a clearance of 0.19-0.23 inches (5-6mm). When complete, position and secure the lower trim panel.
  4.  
  5. Inspect the rubber seal between the master cylinder and booster and replace it if necessary.
  6.  
  7. Install the master cylinder to the booster, followed by the reservoir and hoses.
  8.  
  9. Fill the reservoir with brake fluid and bleed the brake/clutch system.
  10.  

320i MODELS

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.


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

  1. Remove the master cylinder.
  2.  

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

  1. Disconnect the vacuum line at the power booster.
  2.  
  3. Remove the brake pedal apply-rod to power booster pushrod pin from the pedal assembly inside the passenger compartment.
  4.  
  5. Remove the power booster attaching nuts, and remove the power booster from the vehicle.
  6.  

To install:
  1. Position the booster and secure with the attaching nuts tightened to 16 ft. lbs. (22 Nm).
  2.  
  3. Connect the brake pedal rod using the pin removed earlier.
  4.  
  5. Install the master cylinder and brake lines. Reconnect all hoses and vacuum lines.
  6.  
  7. Adjust the extended visible length of the brake light switch head to 0.19-0.23 inches (5-6mm).
  8.  
  9. Bleed the brake system as needed.
  10.  

5 and 6 Series
1975-85 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.


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

  1. Remove the coolant reservoir from the engine compartment.
  2.  
  3. Remove the brake hoses, steel lines and master cylinder. If needed, mark any lines or hose to ease reinstallation.
  4.  

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: Remove the bolts (arrow) to remove the brake booster

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

  1. Disconnect the vacuum hose at the power booster.
  2.  
  3. Remove the driver's side lower trim panel and disconnect the power booster apply rod at the brake pedal.
  4.  
  5. Remove the power booster attaching bolts.
  6.  
  7. Remove the power booster from the vehicle.
  8.  

To install:
  1. Install the booster to the vehicle, tightening the attaching nuts to 16 ft. lbs (22 Nm), and connect the brake pedal rod. Install the master cylinder steel lines and hoses. Reconnect the vacuum line.
  2.  
  3. Adjust the brake pedal distance to 9.0-9.3 inches (230-240mm). Check and adjust the stop light switch distance as described below:
    1. Unfasten the electrical connector and loosen the locknut.
    2.  
    3. Measure the distance between the button on the end of the switch and the brake pedal. It must be 0.19-0.23 inches (5-6mm). If necessary, turn the stoplight switch to adjust the distance.
    4.  
    5. Tighten the locknut and reconnect the electrical connector.
    6.  

  4.  

1986-88 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.


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

  1. Remove all brake fluid from the master cylinder.
  2.  

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

  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the electrical plugs from the cap on the fluid reservoir. Disconnect and cap the hose going to the hydraulic clutch.
  4.  
  5. Tag for identification, then disconnect the two brake lines on the outboard side of the master cylinder.
  6.  

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.

  1. Remove the lower instrument panel trim and remove the brake pedal return spring. Then, remove the retaining clip and pull out the clevis pin connecting the pedal linkage to the booster.
  2.  
  3. Remove the four nuts securing the booster to the firewall. Then, remove the booster and master cylinder from the engine compartment.
  4.  
  5. Remove the two mounting bolts and disconnect the master cylinder from the booster.
  6.  

If the original power booster unit is to be reused, remove the dust boot and clean the silencer and filter. Position the slots in the silencer 180° away from the slots in the filter.

  1. Check the O-ring located in the end of the master cylinder and replace if worn or cracked.
  2.  

To install:
  1. Install the booster/master cylinder using the attaching nuts tightened to 16 ft. lbs. (22 Nm).
  2.  
  3. Install the pedal linkage, clevis pin and return spring.
  4.  
  5. Adjust the stoplight switch as follows:
    1. Disconnect the electrical connector and loosen the locknut.
    2.  
    3. Measure the distance between the button on the end of the switch and the brake pedal. It must be 0.19-0.23 inches (5-6mm). If necessary, turn the stoplight switch to adjust the distance.
    4.  
    5. Tighten the locknut and reconnect the electrical connector.
    6.  

  6.  
  7. If not already done, fill the reservoir with clean DOT 3 or 4 brake fluid and bleed the brake system completely.
  8.  

 
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