Proportioning Valves (Lumina APV, Silhouette & Trans Sport)

System uses 2 proportioning valves, threaded into master cylinder, to regulate brake system hydraulic pressure. See Figure.

Valves allow input pressure to rise to predetermined level before allowing output pressure to rear brakes. This prevents rear wheel lock-up on vehicles with light rear wheel loads. Valves also incorporate a by-pass feature which ensures full system pressure is applied to rear brakes if front brakes lose hydraulic pressure (or if rear brakes lose hydraulic pressure, full pressure is applied to front brakes).