1971 Chevy Camaro Project - Arterial Reconstruction Photo Gallery
A proportioning valve reduces pressure to the rear brakes to prevent them from locking up before the front brakes. This is because the front has the weight transferred to it when you slam on the brakes. The momentum and front-end weight cause the front to get lower and the back of the car go higher. A proportioning valve allows the front brakes to apply more force than the rear to stop the car quicker.