Hi everyone. I know this topic has been covered hundreds of times, but I am stumped right now. Here's my problem:

Ever since I purchased the truck, the BRAKES light just stays on whenever the truck is running (key in ON position).

A few months back I got all new brakes on my truck. On the front, I got new pads (calipers were alright), and there were no leaks. On the back, I had to get all new hardware. One of the rear cylinders was leaking, but I put all new cylinders on there, so no leaks now.

Today, I troubleshooted a little more with the BRAKES light. Read all the posts about the proportioning valve, and they didn't really help me. Here's what I troubleshooted:

Master cylinder and power booster are fine. No leaks. Brake pedal goes down slightly when engine is started, which is normal. Brakes don't use much fluid, if any.

Proportioning valve is pretty wet (but my steering box leaks a little so it could be from that). I took the switch out, and the plunger is pretty stiff, but it moves in and out. I took the switch out, and tried the light with the switch out, but the light didn't come on. Found out that the switch needs to be grounded in order for it to come on? When the plunger of the switch was grounded to the frame, and the plunger pushed in, the light came on. If it was just grounded with the plunger out, then it didn't come on. So it looks like the brake proportioning switch checks out OK.

I tried to put something in the valve to center it again, but not enough room. On my 73 the valve is located on the side of the frame, right underneath the steering box (pain to get to).

Think I have a bad proportioning valve? When I test my brakes when driving, my front wheels lock up when braking on gravel when slamming on the brakes. Back brakes, don't know if they work too well. Think my proportioning valve is the problem.

Any ideas or insights before I try to get either another used proportioning valve or a new one? Any help would be GREATLY appreciated! Thanks in advance!

BTW, my truck has front disc, and rear drum brakes. Front brakes are dual piston.

 

I just recently had the same problem. After i had changed my brake booster and master cylinder do to a bad booster i bled all the lines starting from the farthest one away from the cylinder. Once i completed that it had aligned itself and the light went off. I have also heard of unhooking the line on the master cylinder for the one that is locking up and then pressing brakes and it should move the ball in the valve. Then you have to hook the line back up and bleed the brakes.

 

Sometimes pushing real hard on the brake pedal center the switch in the BPPV.

If you know which circuit of the brake failed and caused the light to come on.. you slightly open the other circuit and press on the pedal to move the switch the other way until the light goes out.

 

I'd try pushing real hard on the pedal with both feet with the engine running. Sometimes the valve piston is hard to recenter.

 

beartracks, I've tried pushing real hard, several times in fact. No luck. The valve's been like that since I purchased the truck. I do notice the truck's idle go down slightly when the brakes are applied, I suspect this is normal.

I guess the brakes could be re-bleeded again, but they've been bled 2 times since the brakes were replaced a couple months back.

 

This might not be a logical solution but it worked for me. I had a 1975 F250 4x4 where the brake light stayed on while the truck was running. The book says that means that there is low pressure in the brake system. All the brakes (drums all the way around) were replaced and the system was bled several times. The light still stayed on. It was irritating, especially at night. The system did not leak and the brakes worked fine. I just unplugged the switch and my problem was solved. I drove the truck for another 15 years. Other than normal maintenance the brakes worked well. It might have been a bad contact or ground but I was tired of chasing the problem. At the time I was young and it was just another malfunctioning idiot light to me.

 

Sorry, No it doesn't mean Low brake pressure.

It means the brakes have failed from fluid loss in either the front or rear brake circuit and the pressure differential valve that is normally centered in the PPV has now moved to one side pushing the pin on the switch up and turning the brake warning light on.

You don't have to RE-BLEED all the brakes.. you simply SLIGHTLY open a bleeder screw on the opposite circuit to what failed then press the brake pedal until the light goes out.. then tighten the bleeder screw....... Done

 

The brake light stays on?

You actually mean the "LOW BRAKE FLUID WARNING LIGHT" in the instrument cluster stays on, right?

Simple fix: The switch that controls it is defective = very common for that to happen.

The switch is plastic and screws into the proportioning valve.

Two things cause it to fail. Either it burns out, or the plastic threads develop cracks.

When cracks develop, brake fluid seeps out...then...the warning light on the dash comes on...and stays on.

C8AZ-2B264-A .. Low Brake Fluid Warning Light Switch. STILL available from Ford.

Fits: All FoMoCo passenger cars 1968/72.

From FTE sponsor DIRECT FORD PARTS / Ford suggested retail price: $29.67 / FTE member net price: $15.73.

Fits: 1968/79 F100/350 / 1968/79 Bronco / 1969/79 Econoline.

Available from Ford and every autoparts store.

 

This happened many years ago and the old mechanic at the Ford dealership told me it was low pressure. Guess he was wrong and I just learned something new. Thanks for setting me straight. I don't mind constructive criticism

 

Wow good advise thanks. I have a '67' ranchero and I think it has been stuck for 30 yrs. so I think I will just replace. The car has factory power discs up front. When you said "pressure differential valve" I knew you were on to something.

 

The brake light on my '76 was on all the time when I bought the truck.
Couldn't fix it so I just unplugged it.
Now it stays off.