Brake Proportioning/Combination Valve: Description and Operation

DESCRIPTION

Proportioning Valve With ABS And Non-ABS TLEV:

Two proportioning valves are used on each vehicle. One valve is used for each rear brake hydraulic circuit on all applications. Antilock Brake System and early production Non-Antilock Brake System applications use in-line proportioning valves that are located in the rear of the vehicle, at each rear brake flex hose. Later production Non-Antilock Brake System applications use proportioning valves that are located in the junction block.
The in-line proportioning valves are not serviceable, but are a replaceable component. The in-junction block valves are not serviceable and must be replaced as part of the junction block.

OPERATION
Proportioning valves balance front to rear braking by controlling (at a given ratio) brake hydraulic pressure to the rear brakes above a preset level (split point). On light pedal applications equal brake pressure is transmitted to both the front and rear brakes. On heavier pedal applications, through the use of proportioning valves, the pressure transmitted to the rear will be lower than the front brakes. This prevents premature rear wheel skid.
If hydraulic pressure is lost in one-half of the diagonally split brake hydraulic system, the operation of the proportioning valve in the remaining half is not affected.