Brake Proportioning/Combination Valve: Description and Operation

Proportioning Valve With ABS And Non-ABS TLEV:

GENERAL INFORMATION
This vehicle uses in-line proportioning valves. The proportioning valves are located in the rear brake tubes on vehicles not equipped with Antilock Brakes or at the rear brake outlet ports of the hydraulic control unit (HCU) on vehicles equipped with Antilock Brakes. The in-line proportioning valves used on this vehicle, replace the combination valve used in prior brake hydraulic systems. With this design, the chassis brake tubes connect directly from the master cylinder or HCU to the brake flex hose at the wheel. The non ABS equipped proportioning valves are located in the same area of the vehicle as the hydraulic unit on ABS equipped vehicles.

FUNCTION
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.

IDENTIFICATION
There are two different styles of 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.