GM Cadillac 1967-1989 Repair Guide

Master Cylinder

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REMOVAL & INSTALLATION



See Figures 1, 2, 3 and 4

The master cylinder can be removed without removing the power vacuum cylinder from the car.

  1. Clean the area around the master cylinder.
  2.  
  3. Disconnect the hydraulic lines at the master cylinder. Plug or tape the ends of the lines to prevent dirt from entering and to prevent fluid from leaking out.
  4.  
  5. Remove the master cylinder attaching nuts and remove the master cylinder.
  6.  
  7. Drain the master cylinder.
  8.  


WARNING
Be careful to keep brake fluid away from all body paint-the fluid acts like paint remover, and a few drops will quickly bubble any paint with which it comes in contact.

  1. Installation is the reverse of the removal procedure. Bleed the master cylinder, brake system and adjust the brake system.
  2.  
  3. To bleed the master cylinder before installing it in the car. Do so in the following manner:
    1. Install plugs in the outlet ports.
    2.  
    3. Place the unit in a vise with the front end tilted slightly downward. DO NOT OVERTIGHTEN the vise.
    4.  
    5. Fill both reservoirs with clean fluid.
    6.  
    7. Using a smooth, round rod push in on the primary piston.
    8.  
    9. Release the pressure on the rod and watch for air bubbles in the fluid. Keep repeating this until the bubbles disappear.
    10.  
    11. Loosen the vise and position the cylinder so the front end is tilted slightly upward. Repeat steps d and e .
    12.  
    13. Place the diaphragm cover on the reservoir.
    14.  

  4.  



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Fig. Fig. 1: Common master cylinder mounting - Unit is secured to the driver's side of the firewall



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Fig. Fig. 2: Removing the brake lines from the master cylinder



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Fig. Fig. 3: Removing the master cylinder mounting nuts



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Fig. Fig. 4: Removing the master cylinder from the power brake booster assembly

OVERHAUL



See Figures 5, 6, 7, 8, 9, 10 and 11

The models covered in this guide are equipped with either Moraine or Bendix master cylinders. The rebuilding kits may differ slightly, but the procedures are the same. Follow the instructions that come with each particular kit.

  1. Remove the master cylinder from the car.
  2.  
  3. Remove the mounting gasket and boot, along with the main cover, then purge the unit of its fluid.
  4.  
  5. Secure the cylinder in a vise, then remove the pushrod retainer and secondary piston stop bolt found inside the forward reservoir.
  6.  
  7. Compress the retaining ring and extract it along with the primary piston assembly.
  8.  
  9. Blow compressed air into the piston stop screw hole to force the secondary piston, spring, and retainer from the bore of the cylinder. An alternative method is to use hooked wire to snag and extract the secondary piston.
  10.  
  11. Check the brass tube fitting inserts and if they are damaged, remove them. Leave undamaged inserts in place.
  12.  
  13. If replacement is necessary, thread a 3 / 16x5 / 8 in. self-tapping screw into the insert. Hook the end of the screw with a claw hammer and pry the insert free.
  14.  
  15. An alternative way to remove the inserts is to first drill the outlet holes to 13 / 64 in. and thread them with a 1 / 4 -20 tap. Position a thick washer over the hole to serve as a spacer, and then thread a 1 / 4 -20 x3 / 4 in. hex head bolt into the insert and tighten the bolt until the insert is freed.
  16.  
  17. Use denatured alcohol and compressed air to clean the parts. Slight rust may be removed with crocus cloth. Never use petroleum based solvents to clean brake parts.
  18.  


CAUTION
Do not polish the aluminum bore of type "A" cylinders with any type of abrasive. Never use any mineral-based solvents (gasoline, kerosene, etc.) for cleaning. It will quickly deteriorate rubber parts.

  1. Replace the brass tube inserts by positioning them in their holes and threading a brake line tube nut into the outlet hole. Turn down the nut until the insert is seated.
  2.  
  3. Check the piston assemblies for correct identification and, when satisfied, position the replacement secondary seals in the twin grooves of the secondary piston.
  4.  
  5. The outside seal is correctly placed when its lips face the flat end of the piston.
  6.  
  7. Slip the primary seal and its protector over the end of the secondary piston opposite the secondary seals. The flat side of this seal should face the piston's compensating hole flange.
  8.  
  9. Replace the primary piston assembly with assembled pieces in the overhaul kit.
  10.  
  11. Moisten the cylinder bore and the secondary piston's inner and outer seals with brake fluid. Assemble the secondary piston spring to its retainer and position them over the end of the primary seal.
  12.  
  13. Insert the combined spring and piston assembly into the cylinder and use a small wooden dowel or pencil to seat the spring against the end of the bore.
  14.  
  15. Moisten the primary piston seals with brake fluid and insert it, pushrod receptacle end out, into the cylinder.
  16.  
  17. Keep the piston pushed in and snap the retaining ring into place.
  18.  
  19. Continue to hold the piston down to make sure that all components are seated and insert the secondary piston stop screw in its hole in the bottom of the front reservoir. Torque the screw to 25-40 inch lbs. (3-4.5 Nm).
  20.  
  21. Install the reservoir diaphragm and cover.
  22.  
  23. It will save time to bleed the cylinder before installing it in the car. Do so in the following manner:
    1. Install plugs in the outlet ports.
    2.  
    3. Place the unit in a vise with the front end tilted slightly downward. DO NOT OVERTIGHTEN the vise.
    4.  
    5. Fill both reservoirs with clean fluid.
    6.  
    7. Using a smooth, round rod (try the eraser end of a pencil), push in on the primary piston.
    8.  
    9. Release the pressure on the rod and watch for air bubbles in the fluid. Keep repeating this until the bubbles disappear.
    10.  
    11. Loosen the vise and position the cylinder so the front end is tilted slightly upward. Repeat steps d and e .
    12.  
    13. Place the diaphragm cover on the reservoir.
    14.  

  24.  

Master cylinder overhaul on cars with power brakes is the same as above.

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Fig. Fig. 5: Master cylinder with plastic removable reservoir



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Fig. Fig. 6: Moraine cast iron master cylinder with integral reservoir



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Fig. Fig. 7: Removing the lock ring from the master cylinder



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Fig. Fig. 8: Removing the primary piston from the master cylinder



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Fig. Fig. 9: Removing the secondary piston from the master cylinder



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Fig. Fig. 10: Removing the seal from the piston



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Fig. Fig. 11: Exploded view of a common master cylinder inner components

 
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