Jeep Wrangler/YJ 1987-1995 Repair Guide

Master Cylinder

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REMOVAL & INSTALLATION



See Figures 1, 2 and 3

The following procedure applies only to vehicles which are equipped with the standard hydraulic braking system, NOT to vehicles equipped with ABS.

For all vehicles equipped with Anti-lock Brake Systems (ABS), please refer to the master cylinder removal and installation procedure found later in the Anti-lock Brake portion of this section.

  1. Disconnect and plug the brake lines.
  2.  
  3. Disconnect the wires from the stoplight switch.
  4.  
  5. Remove all attaching bolts and nuts and lift the assembly from the vehicle.
  6.  

To install:
  1. Position the master cylinder and install the mounting bolts. Torque the mounting bolts to 15 ft. lbs. (21 Nm).
  2.  
  3. Connect the brake lines and bleed the master cylinder and brake system.
  4.  



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Fig. Fig. 1: Disconnecting a brake line from the master cylinder



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Fig. Fig. 2: Unfastening the master cylinder attaching nuts at the brake booster



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Fig. Fig. 3: Removing the master cylinder from the brake booster

OVERHAUL



See Figures 4, 5, 6, 7 and 8

  1. Remove the master cylinder from the vehicle and remove the cover and diaphragm seal. Drain the brake fluid from the reservoir and mount it in a vise.
  2.  
  3. Push the pushrod in and unseat the primary piston snapring. Remove the pushrod, boot, snapring, and pushrod retainer as an assembly. With power brakes, push the primary piston in with a wooden dowel and remove the piston snapring.
  4.  
  5. Remove the primary and secondary piston assemblies. Air pressure applied through the piston stop hole will help in the removal of the secondary piston.
  6.  

Discard both the primary and secondary piston assemblies. They are serviced in the rebuilding kit only as an assembly.



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Fig. Fig. 4: Depress the pushrod and unseat the primary piston snapring



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Fig. Fig. 5: Removing the primary piston snapring



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Fig. Fig. 6: Removing the primary piston assembly



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Fig. Fig. 7: Removing the secondary piston assembly



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Fig. Fig. 8: Master cylinder and snapring, along with the primary and secondary piston assemblies

  1. Clean and inspect the master cylinder. Replace the master cylinder body if the bore is severely scored, corroded, or pitted, cracked, porous, or is otherwise damaged. Check the by-pass and compensator ports to make sure that they are open and not plugged or dirty. Use brake fluid and air pressure to open these passages. Do not use wire.
  2.  

Use only clean brake fluid or an approved cleaning solvent to wash the master cylinder. Do not use any solvent containing mineral oil such as gasoline, kerosene, alcohol, or carbon tetrachloride. Mineral oil harms rubber components.

  1. Check the tube seats in the outlet ports. Replace the seats only if they are cracked, scored, cocked in the bore, or loose.
  2.  
  3. Install the replacement tube seats, if removed, using spare tube fitting nuts to press the seats into place. Be careful that the seats don't become cocked during installation. Make sure that the seats are bottomed. Remove the tube fitting nuts and check for burrs or chips. Rinse the master cylinder in brake fluid and blow out all passages with compressed air.
  4.  
  5. Lubricate the master cylinder bore and secondary piston seal and cups with brake fluid and install the secondary piston assembly in the cylinder bore.
  6.  
  7. Lubricate the seals on the primary piston assembly with brake fluid and install the assembly in the master cylinder bore.
  8.  
  9. Push the primary piston inward with a wooden dowel and install the retaining snapring in the groove of the master cylinder bore.
  10.  
  11. Push in and install the piston snapring.
  12.  
  13. Fill the master cylinder reservoirs with brake fluid.
  14.  
  15. Fabricate and install bleed tubes in the master cylinder. Make sure the tube ends are submerged in brake fluid. Tubes can be fabricated from copper tubing and spare brake line fittings.
  16.  
  17. Using the pushrod or wooden dowel, press the pistons into the bore; then allow them to return under spring pressure. Repeat this operation until all air bubbles cease to appear in the fluid.
  18.  
  19. Remove the bleed tubes. Cap the outlet ports and install the diaphragm seal on the master cylinder cover.
  20.  
  21. Install the master cylinder in the vehicle. Bleed the system.
  22.  

 
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