Dakota 2WD L4-153 2.5L VIN K FI (1989)
Brake Proportioning/Combination Valve: Description and Operation
Combination Differential Valve
Fig 2 Rear Brake Antilock And Combination Valves
COMBINATION VALVE OPERATION
A combination valve is used with the rear wheel antilock system. The valve is attached to a bracket bolted to the master cylinder mounting studs.
The valve bracket is also used to secure the rear wheel antilock valve. The mounting bracket and combination valve are serviced as an assembly.
The valve is securely attached to the bracket.
The valve contains a front disc brake metering valve and a pressure differential valve and switch. The differential switch is in circuit with the red
brake warning light.
Pressure Differential Switch
The pressure differential switch is connected to the brake warning light. The switch is triggered by movement of the switch valve. The purpose of
the switch is to monitor fluid pressure in the separate front/rear brake hydraulic circuits.
A decrease or loss of fluid pressure in either hydraulic circuit will cause the switch valve to shuttle forward or rearward in response to the pressure
differential. Movement of the switch valve will push the switch plunger upward. This closes the switch internal contacts completing the electrical
circuit to the warning light. The switch valve will remain in an actuated position until repair restores system pressures to normal levels.
Metering Valve
The metering valve is used to balance brake action between the front disc and rear drum brakes. The valve meters (holds-off) full apply pressure to
the front disc brakes until the brake shoes are in full contact with the drums. The valve is designed to maintain front brake fluid pressure at 21 -
207 kPa (3 - 30 psi) until the hold-off limit of approximately 807 kPa (117 psi) is reached. At this point, the metering valve opens completely
permitting full fluid apply pressure to the front disc brake calipers.
