RAM 2500 Truck 4WD V10-8.0L VIN W (1997)
Combination Valve: Description and Operation
Pressure Differential Switch
PRESSURE DIFFERENTIAL SWITCH
The pressure differential switch is connected to the brake warning lamp. 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 lamp. The switch valve may
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 rear 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 807 kPa (117 psi) is reached. At this point, the metering valve opens completely permitting full
fluid apply pressure to the front disc brakes.
