RAM 2500 Truck 2WD L6-5.9L DSL Turbo VIN 6 (1998)
Brake Proportioning/Combination Valve: Description and Operation
Combination Valve
GENERAL INFORMATION
The combination valve contains a pressure differential valve and switch, metering valve and a rear brake proportioning valve on 1500 models. The
combination valve/rear brake proportioning valve are not repairable and must be replaced as an assembly.
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 holds-off the initial pressure to the front
disc brakes until the rear brake shoes retracting springs are overcome. The valve is designed to maintain front brake fluid pressure at 241 - 517
kPa (35 - 75 psi) until the hold-off limit of 310 - 689 kPa (100 psi) is reached. At this point, the metering valve opens completely permitting full
fluid apply pressure to the front disc brakes. This reduces front brake lining wear during low deceleration stops.
PROPORTIONING VALVE (1500 Model)
The proportioning valve is used to balance front-rear brake action at high decelerations. The valve allows normal fluid flow during moderate
braking. The valve only controls fluid flow during high decelerations brake stops, when a percentage of rear weight is transferred to the front
wheels.
