Jeep Wagoneer/Commando/Cherokee 1984-1998

Master Cylinder/Pressure Modulator/Power Booster/Accumulator Assembly

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Removal & Installation



See Figures 1 and 2


CAUTION
This brake system uses a hydraulic accumulator which, when fully charged, contains brake fluid at very high pressure. Before disconnecting any hydraulic lines, hoses or fittings be certain that the accumulator pressure is completely relieved. Failure to depressurize the accumulator may result in personal injury and/or vehicle damage.

The master cylinder, pressure modulator, power booster and accumulator are serviced as an assembly only. Do not attempt to disassemble or repair these components.

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the screws holding the windshield washer fluid reservoir. Disconnect the hoses and wires and remove the reservoir.
  4.  
  5. Remove the air cleaner assembly.
  6.  
  7. Disconnect the ABS ECM wiring connectors at the pressure modulator.
  8.  
  9. Disconnect the wiring at the proportioning valve/differential switch.
  10.  
  11. Disconnect the brake line at the coupling on the underside of the proportioning valve.
  12.  
  13. Disconnect the high pressure line at the accumulator block and immediately cap the port to prevent entry of dirt.
  14.  
  15. Place a catch pan below the supply line at the reservoir. Disconnect the hose at the reservoir and discard the fluid drained from the line.
  16.  
  17. Remove the wires from the low pressure switch on the accumulator block, the modulator boost pressure switch and the fluid level switch.
  18.  
  19. Disconnect the front brake lines at the outboard side of the pressure modulator.
  20.  
  21. Inside the car, disconnect the wiring to the brake pedal switch. It may be necessary to remove the instrument panel lower trim for access.
  22.  



Click image to see an enlarged view

Fig. Fig. 1: View of the proportioning valve and related components



Click image to see an enlarged view

Fig. Fig. 2: Cutaway view of the pressure modulator

  1. Remove the master cylinder pushrod bolt; disconnect the pushrod from the pedal. Immediately discard the nuts from the pushrod bolt; they are not reusable.
  2.  
  3. Remove the nuts from the brake mounting bracket studs.
  4.  
  5. Under the hood, carefully pull the hydraulic components and bracket forward until the studs clear the firewall. Lift the assembly up and out of the engine compartment.
  6.  

To install:
  1. Install the pad onto the new bracket and place the bracket with the brake components in place against the firewall. Make certain the studs are correctly seated in the holes.
  2.  
  3. Position the master cylinder/modulator/accumulator on the firewall and tighten the mounting nuts to 27 ft. lbs. (31 Nm).
  4.  
  5. Connect the wiring harness to the low pressure switch, the differential switch, the pressure modulator, the low fluid and boost pressure switches.
  6.  
  7. Inside the vehicle, install the nuts on the mounting studs and tighten them to 31 ft. lbs (42 Nm).
  8.  
  9. Align the brake pedal, the brake lamp switch and the master cylinder pushrod. Install the pushrod bolt. The pushrod bolt must be correctly installed to avoid interference with the bracket. The bolt head must be on the left side of the brake pedal.
  10.  
  11. Use new nuts on the pushrod bolt. The inner locknut should be tightened to 25 ft. lbs. (34 Nm); the outer jam nut should be tightened to 75 inch lbs. (8.5 Nm).
  12.  
  13. Connect the wiring to the brake switch and install the lower dashboard trim, if it was removed.
  14.  
  15. In the engine compartment, connect the brake lines to the proportioning valve.
  16.  
  17. Connect the pressure and return lines to the accumulator.
  18.  
  19. Install the air cleaner assembly.
  20.  
  21. Connect hoses and wires to the windshield washer fluid reservoir and install it in position.
  22.  
  23. Inspect the high-pressure and return lines; make certain they are not kinked or touching the engine.
  24.  
  25. Fill the master cylinder to the MAX level.
  26.  
  27. Connect the negative battery cable.
  28.  
  29. Turn the ignition switch ON ; the pump should start running. Listen for a drop in pump rpm; this shows the pump is pressurizing the system. If there is no drop in pump rpm within 20 seconds, immediately shut the ignition OFF and check for hydraulic leaks.
  30.  

Severe pump damage will result if the pump runs without pressurizing the system for any length of time.

  1. Add fluid to the reservoir as necessary. Do not overfill.
  2.  
  3. Bleed the brake system.
  4.  

 
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