Abstract: A load sensing proportioning valve system for the hydraulic brake system of passenger cars and the like for varying the amount of brake fluid pressure and thus the braking torque at the rear brakes of a passenger car. The system includes a load sensor oriented between a suspension component, such as a supporting spring, and the vehicle frame or body and includes a cavity for incompressible fluid in which variation in load will vary the volume of the cavity for providing increased pressure and volumeric flow of an incompressible fluid from the cavity to a proportioning valve incorporated into the hydraulic brake lines extending from the master cylinder to the rear brakes of a passenger car for regulating the proprotioning valve to vary the braking pressure and thus braking torque to the rear wheels to reduce or eliminate premature rear wheel locking when applying brakes of a lightly loaded vehicle and to maintain adequate braking force for the same vehicle when heavily loaded.