BMW Coupes and Sedans 1970-1988 Repair Guide

Master Cylinder

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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.

REMOVAL & INSTALLATION

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.

Except 3, 5, 6 and 7 Series Models

See Figure 1

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

  1. Remove the air cleaner assembly if necessary.
  2.  
  3. Drain as much brake fluid from the master cylinder.
  4.  



Click image to see an enlarged view

Fig. Fig. 1: From left-to-right, the master cylinder is bolted to the brake booster and pedal assembly-2002 model


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 brake fluid reservoir. The brake fluid reservoir will be mounted in one of two ways: (1) installed directly on top of the master cylinder. In this case, tilt the reservoir to one side and prying carefully from underneath, lift the reservoir off of the master cylinder, or (2) the reservoir is mounted to the inner fender sheet metal by means of retaining bolts. To remove, carefully disconnect the hoses leading to the master cylinder and allow any remaining brake fluid to drain into a container.
  2.  
  3. Mark, then disconnect all brake lines from the master cylinder.
  4.  
  5. Remove the master cylinder-to-power booster attaching nuts, and remove the master cylinder from the booster and vehicle. Observe the correct seating of the master cylinder-to-power booster seal.
  6.  

Check for proper seating of the master cylinder-to-power booster O-ring. Check the clearance between the master cylinder piston and pushrod with a plastic gauge, and, if necessary, adjust to 0.0020 inches (0.05mm) by placing shims behind the head of the pushrod.

To install:
  1. Position the master cylinder onto the studs protruding from the power booster. Install and tighten the attaching nuts to 14 ft. lbs. (20 Nm).
  2.  
  3. Connect the brake lines in their correct order to the master cylinder. Begin installing each line by finger-tightening the connection to prevent any crossthreading. Tighten the fittings to 10 ft. lbs. (14 Nm)
  4.  
  5. Install the brake fluid reservoir and fill with brake fluid.
  6.  
  7. Bleed the brake and clutch (if equipped) system.
  8.  

3 Series Models

See Figures 2 through 7

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.

  1. If working on a 320i, remove the fuel mixture control unit.
  2.  

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

  1. Disconnect the brake fluid level indicator plug, and place aside.
  2.  



Click image to see an enlarged view

Fig. Fig. 2: Use a turkey baster to remove as much brake fluid from the reservoir as possible



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Fig. Fig. 3: Disconnect the wires attached to the fluid cap and the clutch master cylinder hydraulic hose



Click image to see an enlarged view

Fig. Fig. 4: Mark each brake line attached to the master cylinder for correct placement identification



Click image to see an enlarged view

Fig. Fig. 5: Use a flare-end wrench to remove the brake line from the master cylinder



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Fig. Fig. 6: Remove the nuts securing the master cylinder to the brake booster



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Fig. Fig. 7: Lift the master cylinder off the studs and out of the vehicle

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. Unfasten the clutch master cylinder hose at the fluid reservoir. Cap the hose end, or allow it to dip into a suitable container.
  2.  


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 brake fluid from the reservoir, then disconnect the brake fluid reservoir from the master cylinder by unfastening the hoses. Check the condition of each hose and replace if needed.
  2.  
  3. Tag for identification each brake line. Disconnect the brake lines from the master cylinder.
  4.  
  5. On the 320i, work from the underside of the left side inner fender panel (wheel opening area) and remove the two master cylinder support bracket attaching nuts.
  6.  
  7. Remove the master cylinder-to-power booster attaching nuts. Slide the master cylinder out and remove the master cylinder. Inspect the rubber vacuum seal in the end of the unit and replace, if necessary.
  8.  

To install:
  1. Install the master cylinder to the power booster.studs and secure with the retaining nuts tightened to 14 ft. lbs. (20 Nm).
  2.  
  3. Reconnect the brake lines in their correct order. Tighten each fitting to 10 ft. lbs. (14 Nm). Install the fluid reservoir filling with clean brake fluid. Connect the fluid level indicator.
  4.  
  5. Bleed the brake and clutch (if equipped) system.
  6.  

5 and 6 Series Models
WITH VACUUM POWER BRAKES

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.

  1. Remove as much brake fluid from the brake reservoir as possible. Disconnect the brake fluid line going to the clutch master cylinder and plug it or allow it to drip into a suitable container.
  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.


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. Tag for identification, then disconnect the two brake lines connected to the side of the master cylinder.
  2.  
  3. Remove the mounting hardware which secures the master cylinder to the booster. Slide out and remove the master cylinder from the power booster.
  4.  
  5. Inspect the rubber O-ring located in the groove of the rear of the master cylinder. Replace it if damaged.
  6.  

To install:
  1. Install the master cylinder in position, securing the hardware to 18-21 ft. lbs. (25-29 Nm) on the booster. Reconnect the fluid lines tightening to 10 ft.lbs. (10 Nm). Connect all hoses removed earlier.
  2.  
  3. Bleed the the brake and clutch (if equipped) system.
  4.  

WITH HYDRAULIC POWER BRAKES

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.

  1. Depress the brake pedal with maximum force about 20 times to remove all residual hydraulic pressure. Remove as much brake fluid from the brake fluid reservoir as possible using a turkey baster or other suitable clean instrument.
  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.


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 and cap the hydraulic hoses and remove the fluid storage tank from the top of the master cylinder.
  2.  
  3. Remove the mounting hardware fastening the master cylinder to the booster. Slide the unit off and remove it from the vehicle.
  4.  
  5. Check the master cylinder sealing O-ring and replace if needed.
  6.  

To install:
  1. Install the master cylinder on the booster tightening the retaining hardware to 18-21 ft. lbs. (25-29 Nm). Reconnect the brake lines, tightening the fitting to 10 ft. lbs. (14 Nm). Fill the master cylinder and bleed the system.
  2.  

7 Series Models

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.

  1. Remove or drain any brake fluid from the brake reservoir.
  2.  


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.

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. Tag for identification, then disconnect the brake lines from the master cylinder.
  2.  
  3. Remove the master cylinder-to-hydraulic booster attaching bolts, and remove the master cylinder from the vehicle.
  4.  
  5. Check the condition of the master cylinder sealing O-ring and replace if needed.
  6.  
  7. Install the master cylinder on the booster securing the retaining bolts to 18-21 ft. lbs. (25-29 Nm).
  8.  
  9. Reconnect the brake lines tightening the fittings to 10 ft. lbs. (14 Nm).
  10.  
  11. Install the fluid reservoir, and fill with clean brake fluid. Complete the job by bleeding the brake system
  12.  

OVERHAUL



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.

1600, 2000 and 2002 Models

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

  1. Remove the master cylinder as outlined.
  2.  


CAUTION
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. Press in lightly on the piston and remove the stop screw.
  2.  
  3. Remove the circlip and withdraw the piston from the bore. Then, pull off the stop washer, secondary sleeve, spacer ring, secondary sleeve, and stop washer.
  4.  
  5. Unfasten the retaining screw, and pull off the spring cap, spring, pressure cup, and O-ring. Remove and discard the primary sleeve.
  6.  
  7. Using low pressure compressed air, push out the piston. Then, pull off the spring, spring cap pressure cap, primary sleeve, and the O-ring. Lift out the secondary sleeve, and primary sleeve.
  8.  
  9. Clean all parts in methylated alcohol or clean brake fluid. Check the cylinder bore for surface defects. Replace any cylinder or other parts in questionable condition. Prior to assembly, thinly coat all parts with clean DOT 3 or 4 brake fluid.
  10.  

To assemble:
  1. Assemble the master cylinder by first clamping it vertically in a vise to prevent the pressure cap from slipping off during assembly. Then assemble the sleeve making sure that they point in one direction. Coat the space between the secondary sleeve and spacer ring with silicone grease.
  2.  
  3. Coat the piston shank with silicone grease and install into the piston bore. Take care not to damage the rubber sleeves. Finally, push the piston assemblies into the bore, place a new copper washer under the stop screw, then screw in the stop screw, completing the assembly.
  4.  
  5. Install the rebuilt master cylinder into the vehicle and bleed the brake system
  6.  

2500, 2800, Bavaria, 3000 and 3.0 Models

See Figure 8

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

  1. Apply slight pressure to the piston. Remove the stop screw.
  2.  
  3. Remove the circlip, and carefully extract the piston.
  4.  
  5. Pull off the stop washer, secondary sleeve, intermediate ring, and stop washer.
  6.  
  7. Remove the screw from the end of the spring cap, and then remove the spring cap, spring cup, pressure plate, and spacer.
  8.  



Click image to see an enlarged view

Fig. Fig. 8: Note the position of the piston (1) in relation to the stop screw (2)

  1. Use compressed air to carefully remove the piston from the bore.
  2.  
  3. Pull off the spring, spring cup, pressure plate, primary sleeve, and spacer.
  4.  
  5. Clean all parts in alcohol or clean brake fluid. Inspect the master cylinder bore for scratches or pits and replace if necessary. Inspect all parts and replace any that appear excessive worn.
  6.  

To assemble:
  1. Clamp the master cylinder vertically into a vise to prevent the pressure plate from slipping during reassembly. Apply silicone grease to all components, as well as the piston rod.
  2.  
  3. Assemble the master cylinder, noting the following points:
    1. A special tapered sleeve (BMW tool 6063 or equivalent) is available for installation of the piston back into the bore without damaging the seals. Use some sort of sleeve or a least exercise extreme caution in reinstalling the piston so that seal lips do not fold back.
    2.  
    3. Use a new copper gasket under the stop screw.
    4.  
    5. Note that the piston must be inserted far enough into the bore to fully pass the stop screw before the screw is inserted.
    6.  

  4.  


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.

3 Series Models

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.

  1. Push the piston into the bore slightly and remove the stop screw.
  2.  
  3. Remove the circlip and pull out the piston.
  4.  

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

  1. Remove the bearing ring, secondary cups, intermediate ring and the second bearing ring.
  2.  
  3. Loosen the connecting bolt, and pull off the spring retainer, spring, support ring, primary cup, and filler disc.
  4.  
  5. Then, remove the intermediate piston by knocking the housing lightly against a block of wood. Pull off the spring, support ring, primary cup, the filler disc. Remove the separating cups.
  6.  
  7. Clean all parts in alcohol or clean brake fluid. Inspect the master cylinder bore and replace the unit if it is scored or pitted.
  8.  

To assemble:
  1. Note the following when reassembling:
    1. Apply a very light coating of silicone lubricant or cylinder paste to all parts.
    2.  
    3. The new separating cups are marked with a ring of paint. Install them so their lips are opposite each other.
    4.  
    5. Make sure both support rings are positioned properly on the primary cups.
    6.  
    7. When assembling parts to the primary piston (the piston with the rod which protrudes from the master cylinder after assembly), note the following sequence of installation: bearing ring; secondary cups (both pointing in the same direction); intermediate ring; the bearing ring. Coat the space between the secondary cups and intermediate ring with silicone grease.
    8.  
    9. When inserting the pistons into the bore, use a tapered special tool such as BMW 343000 or equivalent, or be very careful to ensure that seal lips do not fold over.
    10.  
    11. Coat the primary piston skirt with silicone grease. Put light pressure on the piston and then install the stop screw with a new copper seal. Make sure the intermediate piston is beyond the stop screw.
    12.  

  2.  

5, 6 and 7 Series Models

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.

  1. Push the piston inward using light pressure, and remove the stop screw. Then remove the circlip and pull out the piston. Remove the stop washer, secondary cup, intermediate ring and bearing ring.
  2.  
  3. Loosen the connecting screw, and pull off the spring washer, spring, support, primary cup, and filler disc.
  4.  
  5. Remove the intermediate piston by knocking the housing against a wooden block lightly. then, remove the spring, support, primary cup, and filler disc and separating cups.
  6.  
  7. Clean all parts in alcohol or clean brake fluid and inspect the bore of the master cylinder carefully for scoring or pitting. Replace those parts damaged or worn.
  8.  

To assemble:
  1. Mount the cylinder in a vise with the bore facing downward at an angle, to prevent the support ring from slipping during assemble. If possible, use a tapered sleeve such as BMW part No. 34 3 000 or equivalent to install the pistons. Otherwise, take care to ensure the seal lips do not double over during installation.
  2.  
  3. Coat all parts with ATE Brake Cylinder paste or a similar silicone lubricant designed for this purpose. Also, keep the following points in mind:
    1. The separating cups are marked with a colored ring and must be installed with their lips opposite each other.
    2.  
    3. Make sure both primary cup supports are located in the primary cups correctly.
    4.  
    5. Install both secondary cups in the same direction. Coat the space between the secondary cups and intermediate ring with silicone lubricant.
    6.  
    7. When installing the piston, apply silicone lubricant to the piston rod and apply light pressure to the rod of the primary piston to push the intermediate piston past the location of the stop screw. Then, install the stop screw with a new copper washer.
    8.  

  4.  

 
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