Combination Valve (Except Silhouette, Trans Sport & Venture)
WARNING: This page does not describe the selected car, but rather 31 other vehicles, including the 1999 Pontiac Montana, 1999 Oldsmobile Silhouette, 1999 Oldsmobile Bravada, 1999 GMC Yukon, and 1999 GMC Suburban. However, it is still accessible from the selected car via links, so may be relevant.
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.
- Warning switch section of valve constantly compares front and rear brake pressures from master cylinder. See BRAKE WARNING LIGHT .
- 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.
Combination valve also contains a by-pass feature. This 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).