Installation and Adjustment of Proportional Valves in Your Car

Figure 1: Proportional valve.

The proportional 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 proportional valve is the key component to a safe, reliable braking system. The instructions below will guide you as how to install a proportional valve.

1. Installation of Your Proportional 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 proportional valve is on the line closest to the engine.

Figure 2: The proportional 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.

Figure 3: You need a pipe cutter.

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.

2. Adjustment after Installation

For safety, start with the proportioning valve set with maximum reduction setting, knob fully screwed out, and work from there. Next, find an assistant to observe and an empty parking lot with no chance of hitting anything. You'll need to repeatedly stop from 30 mph with the wheels locked up without attracting too much attention.

Figure 4: Adjustment after installation.

1. Make sure your tires are correctly inflated to the recommended pressures.
2. For best results, you'll want half a tank of gas or less, no passengers, and minimal junk in your trunk.
3. Accelerate to 30 mph, then stop hard enough to lock up the wheels.
4. Have your assistant watch (from a safe distance) and confirm that the front and rear wheels lock.
5. If only the front locked, adjust the knob in two full turns to allow more pressure to the rear brakes and test again.
6. Continue adjusting in, two turns at a time, until the front and rear wheels lock in a hard stop.
7. Adjust knob out one complete turn and test again.
8. Continue these adjustments 1/2 turn in or out at a time until maximum braking can be achieved and no wheel rear lock is observed.
9. Test the vehicle again at 50 mph to judge the effects of a more dramatic weight transfer and make any additional adjustments as needed. Typically by turning the knob out to decrease pressure to the rear.

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