The proportioning valve is mounted between the brake line master cylinder and the rear wheels. It's designed to adjust the pressure between the front and rear brakes, depending on how hard you're stopping. The shorter the stopping distance, the more of the vehicle's weight is transferred to the front wheels. This will cause the rear wheels to lift and the front wheels to "dive" down. The valve controls how much pressure is applied to each of the braking system's axle sets. In the case of the short stop, it will direct more pressure to the front wheels and less pressure on the rear wheels. The proportioning valve is the key component to a safe, reliable braking system [source: Ofria]. The instructions below will guide you as how to install a proportioning valve.

  1. Check your owner's manual and familiarize yourself with your car's braking system
  2. Find the master cylinder. You will see two brake lines coming out of the master cylinder. The proportioning valve is on the line closest to the engine.
  3. Remove the old valve by cutting it off from both sides of the line. Use a pipe cutter for this step. Slide the new valve in place, attaching it with a pipe thread seal. The valve should be placed near the anti-lock brake system (ABS) control unit.
  4. Make sure the valve isn't touching or rubbing against any brake lines, as this will cause wear and tear, and can endanger the passengers in the car.
  5. Once the new valve is in place, bleed the brakes, to remove any air trapped in the line.
  6. Add as much new brake fluid as is necessary to reach the appropriate level.
  7. Take the car for a test drive and make sure the brakes are working properly [source: Do It Yourself].