Mitsubishi Pick-ups and Montero 1983-1995 Repair Guide

Hydraulic Unit



To test the hydraulic unit a special Mitsubishi scan tool and an oscilloscope would be needed. Therefore, if the ABS warning light comes on or a problem with the ABS is evident, have the system diagnosed by an automotive mechanic familiar with the Mitsubishi ABS systems. After the vehicle has been diagnosed and the cause is known, the defective part can be replaced at home.


See Figure 1

Removal of this unit requires extreme care in handling and operation under the cleanest possible conditions. The slightest bit of dirt can foul the system. Do not disassemble the lines unless suitable plugs for both the lines and ports are immediately available. The need for extreme cleanliness cannot be overstated!

The hydraulic unit is located in the engine compartment, attached to the right-hand fender by the firewall.

  1. Disconnect the negative battery cable.
  3. Drain the brake fluid from the system.
  5. Remove the retaining screws and remove the connector bracket from the top of the relay and hydraulic unit.
  7. Loosen and detach the five brake lines from the hydraulic unit. Make sure to not bend or reform any of the hard lines. Have rags handy since some brake fluid will have been retained in the unit. Make sure to keep the fluid off of any painted surfaces.
  9. Unplug the engine compartment wire harness from the hydraulic unit.
  11. Remove the hydraulic unit bracket from the fender and disconnect the ground cable from the bracket.
  13. Remove the hydraulic unit and bracket from the vehicle.

The hydraulic unit is heavy, so care should be taken when removing it. The hydraulic unit is not to be disassembled; its nuts and bolts should absolutely not be loosened. The unit must not be dropped or otherwise subjected to impact shocks. It must not be turned upside down or laid on its side.

  1. At this time the relay box cover, valve relay and motor relay can be removed from the top of the hydraulic unit.

Click image to see an enlarged view

Fig. Fig. 1: ABS hydraulic unit removal and installation components-1992-95 Monteros

To install:
  1. Affix the motor relay, the valve relay and the relay box cover to the top of the hydraulic unit.
  3. Install the hydraulic unit into the hydraulic unit bracket and secure in position with the retaining bolts and nuts.
  5. Mount the hydraulic unit bracket into the engine compartment and tighten the mounting bolts until snug. Make sure to reattach the ground cable.
  7. Plug the engine compartment wire harness connectors back together.
  9. Install the brake pipes to the hydraulic unit. Tighten the brake pipe flare nuts to 11 ft. lbs. (15 Nm).
  11. Set the connector bracket in place and secure it there with the retaining screws.
  13. Connect the negative cable back to the battery.
  15. Fill the master cylinder with fluid and bleed the system. Make sure that the master cylinder never falls below half full.
  17. Have hydraulic unit tested by a mechanic familiar with Mitsubishi vehicles.