Combination Valve

The combination valve has three sections. Each section serves a different function.

• The metering, or hold off, section limits front disc brake pressure, allowing just enough pressure to overcome the rear brake shoe springs. When the inlet pressure is below 200 kPa (30 psi), there is no restriction. This allows for pressure equalization when the brakes are not applied.
• The pressure differential warning switch constantly compares front and rear brake pressures from the master cylinder. The switch activates the BRAKE warning lamp when a malfunction occurs in the front or rear brake system. The switch latches in the warning position after a malfunction occurs. To turn off the lamp, you must repair the malfunction and apply enough pedal pressure in order to develop about 3100 kPa (450 psi) brake line pressure.
• The proportioning section limits brake line pressure to the rear brakes after a predetermined rear input brake line pressure is reached. This minimizes rear wheel lockup on vehicles with light rear wheel loads. The bypass feature on the combination valve ensures full system pressure to the rear brakes when there is a malfunction in the front brake system