Brake Proportioning/Combination Valve: Description and Operation

Proportioning Valve With ABS And Non-ABS TLEV:

This vehicle uses proportioning valves that are inline with the rear brake tubes. The chassis brake tubes connect directly from the master cylinder or HCU (ABS models) to the rear brake flex hose. The non-ABS brake system uses two proportioning valves in-line with each of the rear wheel chassis brake tubes. The proportioning valve can be identified by its bar code label and stamp. Be sure a replacement proportioning valve has the same stamp as the proportioning valve being replaced.

Proportioning Valve Location For Antilock Brake Equipped Vehicles:

On vehicles equipped with antilock brakes, the proportioning valves are located under the vehicle on the passenger side just rearward of the passenger seat. The proportioning valves mount directly in the chassis brake tube going to each of the vehicles rear brakes.

The ABS proportioning valves function the same as the proportioning valves in the base brake system.

For additional information and procedures on proportioning valves on vehicles with ABS, refer to the Antilock Brake System.

Proportioning Valve For Non-ABS Equipped Vehicles:

Vehicles not equipped with ABS have the proportioning valves located on the front suspension crossmember in the same area as the hydraulic unit mounts on ABS equipped vehicles.

Proportioning valves balance front to rear braking by controlling at a given ratio, the increase in rear brake system hydraulic pressure above a preset level (split point). Under light pedal application, the proportioning valve allows full hydraulic pressure to be applied to the rear brakes.

Proportioning Valve With ABS And Non-ABS TLEV:

There are two proportioning valve assemblies used in each vehicle. During any service procedures, identify valve assemblies by supplier part number and or the bar code label and stamp identification band. This vehicle's brake system uses different calibrations for the proportioning valves. For a vehicle equipped with front disc and rear drum brakes the split point is 600 psi and the slope is 0.59. For a vehicle equipped with front and rear disc brakes the split point is 500 psi and the slope is 0.43.