Repair Pontiac Mid-size 1974-1983 Repair Guide

Master Cylinder



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Fig. Fig. 1 On vehicles equipped with power brakes, the master cylinder is mounted to the power brake booster

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Fig. Fig. 2 The master cylinder is mounted directly to the firewall on vehicles without power brakes

On power brake-equipped models, the master cylinder can be removed without removing the power vacuum cylinder from the car.

  1. Use a clean syringe to remove as much fluid from the master cylinder as possible.
  3. Clean the area around the master cylinder.
  5. 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.
  7. Remove the master cylinder attaching nuts and remove the master cylinder.
  9. Installation is the reverse of the removal procedure. Bleed the brake system, as outlined later in this section.

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.

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Fig. Fig. 3 To remove the master cylinder, drain as much fluid as possible from the reservoir using a syringe

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Fig. Fig. 4 Use a flare-end wrench (see arrow) to disconnect the brake fluid lines from the master cylinder

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Fig. Fig. 5 Unfasten the master cylinder-to-power booster (or firewall on manual brakes) retaining nuts ...

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Fig. Fig. 6 ... then remove master cylinder from the vehicle


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Fig. Fig. 7 Exploded view of the master cylinder-late model vehicles with plastic, removable reservoir

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Fig. Fig. 8 Exploded view of the early model Moraine cast iron master cylinder with integral reservoir

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.

Overhaul procedures for power brake master cylinders and manual master cylinders is the same.

  1. Remove the master cylinder from the car.
  3. Remove the mounting gasket and boot, and the main cover, and purge the unit of its fluid.
  5. Secure the cylinder in a vise and remove the pushrod retainer and secondary piston stop bolt found inside the forward reservoir.
  7. Compress the retaining ring and extract it along with the primary piston assembly.
  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.
  11. Check the brass tube fitting inserts and if they are damaged, remove them. Leave undamaged inserts in place.
  13. If replacement is necessary, thread a 6-3X 5 / 8 in. self-tapping screw into the insert. Hook the end of the screw with a claw hammer and pry the insert free.
  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 in.-20 tap. Position a thick washer over the hole to serve as a spacer, and then thread a 1 / 4 in.-20X 3 / 4 in. hex head bolt into the insert and tighten the bolt until the insert is freed.
  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.
  19. 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.
  21. Check the piston assemblies for correct identification and, when satisfied, position the replacement secondary seals in the twin grooves of the secondary piston.
  23. The outside seal is correctly placed when its lips face the flat end of the piston.
  25. 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.
  27. Replace the primary piston assembly with assembled pieces in the overhaul kit.
  29. 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.
  31. 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.
  33. Moisten the primary piston seals with brake fluid and push it, pushrod receptacle end out, into the cylinder.
  35. Keep the piston pushed in and snap the retaining ring into place.
  37. Relax the pressure on the pistons and allow them to seek their static positions.
  39. Replace the secondary piston stop screw and torque it to 25-40 inch lbs.
  41. Replace the reservoir diaphragm and cover.