Brake Proportioning/Combination Valve: Description and Operation

The non-serviceable brake combination valve is located under the hood, mounted to the Antilock Brake System (ABS) modulator on the left engine compartment side inner rail. The brake combination valve incorporates the following functions into, a single component:

BRAKE PRESSURE DIFFERENTIAL WARNING SWITCH
The brake pressure differential warning switch monitors the front and rear brake systems to measure any difference in hydraulic pressure between the two systems. If a sufficient pressure differential exists between the systems, an electrical ground is made energizing the red "BRAKE" wanting lamp if the ignition is on. The brake combination valve and brake pressure differential warning switch are also designed so the warning switch will latch in the warning position once a malfunction has occurred. The "BRAKE" warning lamp will turn off only after the malfunction is repaired and a pedal force sufficient to develop approximately 31OO kPa (450 psi) hydraulic brake pressure is applied.

BRAKE PROPORTION VALVE
The brake proportion valve improves front-to-rear brake balance under severe brake applications. Severe brake applications transfers part of the vehicle's rear weight to the front wheels. The resulting decrease in weight at the rear wheels can cause reduced brake efficiency. The brake proportion valve limits the pressure to the rear brakes to reduce the tendency for reduced brake efficiency. The proportion valve also has a by-pass feature which assures full system pressure to the rear brakes in the event of a front system brake failure. Full front system pressure is retained in the event of rear brake system malfunction.