Height-Sensing Proportioning Valve ("C" & "K" Series & "P" Series)
WARNING: This page does not describe the selected car, but rather 35 other vehicles, including the 1992 Pontiac Trans Sport, 1992 Oldsmobile Silhouette, 1992 Oldsmobile Bravada, 1992 GMC Yukon, and 1992 GMC Vandura Special. However, it is still accessible from the selected car via links, so may be relevant.
Valve senses vehicle load conditions through relative movement between rear axle and body. See Figure and Figure. As vehicle load increases (resulting in decreased vehicle height), valve allows higher pressure to rear brakes, resulting in optimum front-to-rear brake pressure balance.
WARNING:
On vehicles with height sensing proportioning valve, use of aftermarket load leveling kits, air shocks, or modifications that change axle-to-frame distance will provide a false reading to valve. False readings may result in unsatisfactory brake performance.