Brake Proportioning Valves are designed to control the volume of brake fluid that travels to the brake calipers and wheel cylinders. On early 240Z's, it is located in the rear of the car (not to be confused with the Pressure Differential Switch in the engine bay) ahead of the distribution block and is designed to prevent the rear wheels from locking under rapid braking. If your rear wheels lock up when applying the brakes normally, you should inspect the Proportioning Valve for faults. While replacement valves are not available, the most common problem that these valves have is that the internal seals go bad over time. This kit includes all three seals needed to properly rebuild your valve.