Brake Proportioning/Combination Valve: Description and Operation

PROPORTIONING VALVE

DESCRIPTION
Proportioning valves are included on vehicles without Antilock Brakes (ABS). They are located in the junction block.

NOTE: Vehicles with ABS do not have proportioning valves. They have electronic variable brake proportioning (EVBP).

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.