I have a question for the electrical system experts. I have a 1972 F250 Camper Special. There is a red emergency brake light at the lower left corner of the dash just above the emergency brake release handle. The light stays on whether the emergency brake is on or off. I cannot find anything in the emergency brake foot assembly that looks like a switch. The truck has power brakes which appear to be working OK though the pedal seems a little hard for power brakes. Nothing like manual brakes though.

My father bought this truck new and I remember as a kid that the light went out when the emergency brake was released. Boy, that was moons ago.

Can anyone tell me how to get the light to go out when the emergency brake is released?

Thanks.

 

Hi and welcome to FTE!

That light is not for the parking brake even though it's down there by it. It's a warning light for the brake system. It's on when either half of the dual brake system has low pressure or leakage. Did it just come on recently? Did the hard pedal occur around the same time? I would go over the whole brake system and check things out first to be safe.

Barry

 

The light is not related to emergency brake. The light is the low brake pressure warning light. It's purpose is to warn you if you loose hydralic pressure in either the front or rear brake system. The light is adjusted to the off position by bleeding your brakes according to the manual if you have one. Otherwise, I imagine this site has the procedure in writing somewhere. Some people just disconnect the wire, but that's cheating. As an owner you really should know how to the system operates. It must be adjusted (bled) everytime you do a brake job. More importanly, it let's you know if you have a problem such as a broken line.

 

Mine has been on for years. I've rebuilt or replaced everything (because it needed it), brakes are fine. I read somewhere years ago that the device that switches the light on can be stuck. I haven't messed with trying to unstick it.

 

It's not that the switch is stuck, after it switches you need to manually re-center the switch to turn the light off.

barry

 

The switch is part of the proportioning valve; how do you recenter the switch? I unhooked mine as well, but would like to hook it back up if I just need to adjust something to make it function properly again.

 

It would be good to know what side of the system failed or was bled last. What you do is turn the ignition switch to ACC (to light the lamp) and crack open the differential valve inlet tube nut of the unfailed system or the side opposite the system that was bled last. Carefully depress the brake pedal gradually until the pressure differential valve centers itself and the warning light goes out. Then tighten the tube nut.

If you don't know what side to crack open, try it on one side and if the light won't go out, try the other side. Also if you have a power booster, pump it several times to bled off all the vacuum first before doing this.

Barry

 

I wasn't aware so many were unfamiliar with the warning light. Yes, they do stick. To repair, you must remove the valve assembly from vehicle. BUT, normally light will go off when you bleed the brakes properly. I suggest that bleeding shoud be done at the front or rear brake wheel cylinder bleed fitting rather than the tubing nut at the valve. Much cleaner and easier.

You really should have a diagram of the valve so you understand what you are bleeding for. There is a sliding piston with an indented center section inside the vavle bore. The bore in the valve has two identical chambers at each end which allows the piston to slide back and forth. Try to picture a 1/4 diameter x 2"long (approx) round brass rod(piston) that is necked down in the middle. At each end of the bore chambers two hydralic lines are connected. One line allows pressure in from the front brake section of the master cylinder to one end of the bore in the valve. The other line at that same end of the bore allows pressure out from the valve to the front wheel cylinders. This is repeated for the rear brakes at the other end of the valve bore. Sometimes the front brake portion of the valve will run two lines to the front brakes for a total of 3, (1 line in from master cylinder and 2 lines out one to each side of front brakes).

So, you should have a minimum of 4 brake lines (sometimes 5) at the valve - two into the valve from the master cylinder and at least 2 out, one for each front and rear brake system. the light goes out when the sliding piston is centered. That is, the indented section is in the middle of the bore directly below the electric wire conncetion on the valve. When the indented section is below the electric fitting a second sliding rod, this one inside the electric fitting, slides perpendicular down into the indented section of the brass rod in the bore. When the electric fitting rod slides down, the circuit is broken to the light and it goes out at the dash. The piston is centered properly by bleeding the front or rear wheel cylinders. The piston slides in its bore to the area being bled due to reduced pressure on the bleeding side.

The only way to bleed this sytem is to use 2 people. One presses the brake pedal very SLOWLY until the light goes out. The second person is bleeding at the wheel cylinder. If you don't know which end of the bore the sliding piston is located, then trial and error is the only way to start. That is, you bleed one cylinder, say the front, while your buddy is slowly depressing the pedal and watching for the light to go out. As soon as it goes out he stops depressing the pedal and you tighten the bleed valve. If the light goes out and then comes back on, you have bled too much resulting in the piston sliding past the center and pushing up the perpendicular electric fitting rod. This makes the circuit again to the light. If so, go to the rear end bleed just enough to slide the piston back to its center and the light will go out.

If the light does not go after a few tries, then go to a rear wheel cylinder and repeat process. If it doesn't go out either way, piston in valve is probably stuck, or possibly the sliding rod in the electric fitting is stuck. You can test the electric fitting simply by unscrewing it allowing the sliding rod to break contact and the light goes out.

At the valve itself is a removable brass plug at one end of the valve bore. You can remove it and push the sliding piston to center it. BUT only if luckily enough for the piston to be stuck at that end of the bore. Otherwise ingenuity is needed , It can be done. Or, maybe go to junk yard and replace with another valve.

This confusing without diagrams. Try to find one. they are out there, i.e. service manuals. Motor Manual, Brake manufacturer's literature.

 

After I bled out the system on my '69 Ranger, the light stayed on. Now, this truck had sat for many years with no brake fluid in the system before I bought it so I was afraid the switch might be stuck. However, I just bled the switch like you would bleed the brakes at the wheels, and the light went off.

 

Great info!

I should clarify what I said so people don’t think I’m an idiot. Yes, the valves do stick but usually if the light came on it doesn’t mean it’s stuck, just needs recentering. When they stick the bleeding procedure won’t recenter it.

Two people are definitely the way to go at this but I’ve done it myself, after several tries! Doing it at the wheel cylinders is a lot neater plus there’s no guessing what tube is what at the pressure differential valve.

Barry

 

Thanks to all who responded to my inquiry by an emergency brake light staying on. Sounds like my question was of interest to several of you. Since I recently had the brakes redone professionally, they obviously didn't know what the light meant either and did not recenter the proportioning valve when the bled the brakes. So, back to them to get this problem solved. Again, thanks for your assistance