With Disc Brakes

Fig. 4 Gauge hook-up for testing proportioning valve (typical):

The proportioning valve (when used), Fig. 4, provides balanced braking action between front and rear brakes under a wide range of braking conditions. The valve regulates the hydraulic pressure applied to the rear wheel cylinders, thus limiting rear braking action when high pressures are required at the front brakes. In this manner, premature rear wheel skid is prevented.