On vehicles without ABS, the proportioning valve is located along the right side of the engine compartment bulkhead. ABS equipped vehicles have the proportioning valve attached to the hydraulic modulator. The proportioning valve limits outlet pressure to the rear brakes after a predetermined pressure has been reached.

The valve has a by-pass feature which ensures full system pressure to the rear brakes in the event of a front brake failure. Conversely, full front pressure is retained in the event of a rear brake pressure failure.