the red brake light on my 84 F250 just wont shut off. It used to work fine until one of my brake lines busted and i replaced all the front brake components, new calipers, pads, lines, sliders. I bled the lines and the pedal doesnt feel mushy. Is there something i need to reset? Wheres the sensor for this light? Also, aving the parking brake on or off makes no diffrence in the light.

 

There is a wire going to the proportioning valve. If you take the wire off, the light will probably go off.

What happens is the proportioning valve has the front brake system and the rear brake system both in the one housing. The only thing seperating the two systems is a plunger. If the pressure in both the front and the rear is equal, then the plunger stays centered, and the light stays off. Since you busted a front line, the pressure dropped in the front and stayed high in the rear, so the rear pressure pushed the plunger forward and turned the light on.

After you go it fixed, the plunger did not re-center itself. So what you can try to do is open a rear bleeder and hit the brakes hard. This may push the plunger back to center and turn the light off.

 

I see, i might try to recenter it if the bleeders arent siezed up, but the light is just annoying, so i might pull the plug.

 

To reset the light is a two person operation. You will need to break the line going to the rear brakes loose at either the master cylinder or at the porportioning valve. Turn the key on and have someone gently push down the brake pedal. Have him yell out when the light goes off. Have him hold the brake pedal at that point and tighten the line back up. Let up on the pedal and then step on it again. The light should stay off. It might take a time or two to get the feel of it, but that is a pretty good way to do it.

Hope that helps,

Dan Harriman 84 F150 lwb
Orange, Texas

 

I see sounds like a plan. Thatll be a good project. Thanks for all the help.

 

If this is the switch that controls the low brake fluid warning light on the dash, it has a tendency to leak brake fluid. What happens is the plastic switch, which screws into the brass proportioning valve, develops minute cracks around the threads. This allows just enough brake fluid to seep past, activating the switch. The light on the dash comes on, and stays on.


D5AZ-2B264-A .. Low Brake Fluid Warning Light Switch

 

I did the operation today and it fixed my problem. No more annoying red light! Thanks for all the help.

 

Sounds like the same problem with my 84 F250. I was very concerned that it might be a "cold weather issue" because it started staying on right after trying to get my 6.9L started the other morning at 17 degrees. Guess I will check out bleeding the brakes to center the plunger.

hugger94