Brake Proportioning/Combination Valve: Description and Operation

Proportioning Valves For Non ABS Equipped Vehicles:

This vehicle uses screw-in proportioning valves inline with the rear brake tubes. The chassis brake tubes connect directly from the master cylinder or Hydraulic Control Unit (HCU) (on ABS vehicles) to the brake flex hose. The brake system uses two proportioning valves in-line with each of the rear wheel chassis brake tubes. The non-ABS equipped proportioning valves are located on the front suspension crossmember in the same area where the integrated control unit mounts on ABS equipped vehicles.

Proportioning Valve Location For ABS Equipped Vehicles:

On vehicles equipped with antilock brakes, the proportioning valves are located at the rear of the vehicle. Each proportioning valve mounts directly to the flex hose for the rear wheel brakes and has the chassis brake tube for each rear brake connected directly to it.

Proportioning valves balance front to rear braking by controlling at a given ratio, to increase the 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. Due to differences in thread sizes, each proportioning valve has a different part number. During any service procedures identify valve assemblies by supplier part number and or the bar code label and stamp identification band. All vehicle brake systems use a common calibration for the proportioning valve. The split point is 500 psi and the slope is 0.43 on rear drum brake vehicles. Vehicles with rear disc brakes have a split point of 400 psi and a slope of 0.34.