A load sensing proportioning valve (LSPV) is installed in the rear brake line on some late model vehicles.
Brake fluid pressure, from the master cylinder, to the rear wheels is controlled by the LSPV according to the vehicle loading conditions, i.e., weight carried. Adjusting the pressure to the rear wheels, depending on the load, improves straight line stopping and helps prevent rear wheel lock up.
The LSPV is connected to a rear lateral rod by a link, lever, cable, and spring. The space between the vehicle floor and lateral rod determines the amount of pressure adjustment to the rear wheels. When the space is greater (light load), the spring pressure to the LSPV is light and less brake pressure is applied. As the vehicle load is increased, so is the LSPV spring pressure and more braking pressure to the rear wheels is provided.
- Park the unloaded vehicle on a level surface. Do NOT support the vehicle on a jack or other support.
- Measure the length, of the spring, between the attaching holes in the fixed end of the LSPV and the operating lever. The length should be 89-91mm.
- If the length of the spring is not correct, adjust it to the correct length by turning the adjusting nut at the end of the cable located on the opposite side of the operating lever.