Combination Valve (Except Lumina APV, Silhouette & Trans Sport)

System uses a combination valve to regulate brake system hydraulic pressure. Combination valve, located in brake lines between master cylinder and wheels, has 3 pressure control functions:

• Metering (or hold-off) section of valve limits pressure to front brakes until pressure of rear brake shoe retractor springs is overcome, then allows pressure to front brakes.
• Proportioning section of valve allows 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.
• By-Pass section of valve ensures full system pressure is applied to rear brakes if front brakes loses hydraulic pressure (or if rear brakes lose hydraulic pressure, full pressure is applied to front brakes).

Combination valve also contains a pressure differential warning switch. See BRAKE WARNING LIGHT under DESCRIPTION & OPERATION .