GM Cutlass RWD 1970-1987 Repair Guide

Master Cylinder

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REMOVAL & INSTALLATION



See Figures 1, 2, 3, 4, 5 and 6

Vacuum Power Brakes

On cars with power brakes, the master cylinder can be removed without removing the vacuum booster from the car.


WARNING
Only use flare nut wrenches when removing the brake lines from any component. Standard wrenches will damage the flare nut and line.



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Fig. Fig. 1: Master cylinder mounting on cars equipped with vacuum power brakes



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Fig. Fig. 2: Exploded view of a master cylinder, 1978 and later shown, other years similar



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Fig. Fig. 3: Exploded view of a master cylinder - Diesel V8

  1. Clean the area around the master cylinder.
  2.  
  3. Disconnect the hydraulic lines from the master cylinder. Cap the lines to prevent fluid from leaking or contamination of the brake fluid.
  4.  
  5. Remove the master cylinder attaching bolts.
  6.  
  7. Remove the master cylinder and drain the fluid.
  8.  



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Fig. Fig. 4: Use a flare nut wrench when removing the brake lines



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Fig. Fig. 5: Remove the master cylinder attaching nuts



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Fig. Fig. 6: Remove the master cylinder from the vehicle

OVERHAUL



See Figures 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 vehicle.
  2.  
  3. Remove the mounting gasket and boot, and the main cover, and purge the unit of its fluid.
  4.  
  5. Secure the cylinder in a vise and remove the pushrod retainer and secondary piston stop bolt found inside the forward reservoir (Moraine iron cylinder only).
  6.  

The plastic composite master cylinder reservoir can be removed by prying against the cylinder and reservoir. Work the reservoir from the rubber grommets using care not to damage either component.

  1. Compress the retaining (lock) ring and extract it along with the primary piston assembly from the end of the bore.
  2.  



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Fig. Fig. 7: Compress the primary piston and remove the lock ring



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

  1. Blow compressed air into the piston stop screw hole, if equipped, 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.
  2.  
  3. Check the brass tube fitting inserts and if they are damaged, remove them. Leave undamaged inserts in place.
  4.  
  5. If replacement is necessary, thread a 3 / 16 in. x 5 / 8 in. self-tapping screw into the insert. Hook the end of the screw with a claw hammer and pry the insert free.
  6.  
  7. 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 in.-20 tap. Position a thick washer over the hole to serve as a spacer, and then thread a 1 / 4 in.-20 x 3 / 4 in. hex head bolt into the insert and tighten the bolt until the insert is freed.
  8.  
  9. 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. Also, a brake hone is helpful in removing varnish and slight rust.
  10.  



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Fig. Fig. 9: Use compressed air to aid in the removal of the secondary piston from the master cylinder



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Fig. Fig. 10: Seals can be removed from the piston with a small pick or awl



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Fig. Fig. 11: Internal components of a master cylinder

To assemble:
  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 clean 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 push it, pushrod receptacle end out, into the cylinder.
  16.  
  17. Keep the piston pushed in and snap the retaining (lock) ring into place.
  18.  
  19. Relax the pressure on the pistons and allow them to seek their static positions.
  20.  
  21. Replace the secondary piston stop screw and torque it to 25-40 inch. lbs. (3-4 Nm), if so equipped.
  22.  
  23. Replace the reservoir diaphragm and cover.
  24.  
  25. Install the master cylinder and bleed the entire system.
  26.  

 
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