Today I replaced the rear brake line from the master cylinder to the proportioning valve on my '71 F250. While I was down there I noticed a wire hanging down near the proportioning valve. I looked on my parts truck and sure enough there it was there but plugged into the valve. Hrmm ok so I thought and tried to plug mine back in. No luck too much corrosion to allow the joint to fit right. Can anyone please tell me what this wire is supposed to do? Brakes work great now after the line replacement and my brake lights work so i'm not real sure what it's for.


Thanks all

N3

 

That's the Brake failure light.

It comes on when you lose pressure in one of the circuits.

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ahh ok thanks :7 makes sense why everything works then.

N3

 

Hello if you get that wire plugged back in their is a little light on the dash in the bottom left corner (at least in the 1970s) It may come on. Instead of just pulling the wire out as sombody else probably did you can bleed the brakes to make it shut off. Just turn the ignition on and bleed the front slowly to make the switch return to a nutral spot. If that dosn't work go around to the back and try there. Actually you should probably start in the back becaust when you bleed the brakes you are supposed to start with the longest line then the next shortest ect. If you have bled the brakes recently and remember if you did the front or back last bleed the end you did first. Ths may seem confusing, but you should try figuring it out wihout a manual, thats tricky! If you have any other questions I will try to help. My uncle dug up an old manual (after i had to figure this out).


Scott.

 

Hmm..that's funny. I bled my brakes twice and the light still hasn't gone off. I always start from rr,lr,rf,lf but maybe I should change the rotation. Another question actually. I just replaced my Master cylinder on my 68 f-250. with drums all round. Are the two chambers in the master cylinder supposed to be the same size. Mine are different.
Thanks

 

Yes it is normal. I have a smaller resivoir in the front and a larger in back. It might have somthing to do with the fact that the rear brake lines are longer, and it is more conveniant to have a larger res. for the back brakes. Quick question are your power or manual?

 

Another thing yours is a 1972? Some of the warning light moduals need to be replaced, they cant just be reset. I will see if I can find out for you. My 1970 can be reset. T will get back to you this evening, (stuck in school all day)

Scott



Would rather be working on my truck!

 

my brakes are manual. I'm going to try bleeding from the front back to see if I can equalize the proportionning valve. I guess that I can't expect everything to work on a 68...

 

I also have a '68 F100 that had a stuck proportioning valve. The previous owner just broke the little light instead of fixing the problem. I tried re-centering by bleeding but that didn't work. I finally had to remove one of the fittings on the end of the valve and push it back with a punch until it was centered and free and then rebleed the brakes. Now it works fine.

 

do what scott says. if your light stays on after you fix the wiring. read the manual under 'centralizing the pressure differential valve'.

 

Bauld; Firstly our friend Inliner has the right answer if the “bleeding to center the valve” trick doesn’t work. I'll give a short explanation of what happens in the combination valve when a brake system failure occurs. The plan is to save braking action on at least two wheels usually front or rear in the event of catastrophic loss of line pressure. Responding to a lack of pressure in one half of the brake system the safety valve moves to block off that portion of the brake system and turns on the warning light by providing a ground for the circuit. This happens whenever there is a rapid loss of line pressure, either through a leaking wheel cylinder, broken line or when you loosen the bleeder screw. When the pressure is equalized by opening a bleeder screw on the side that has residual pressure the valve re-centers. Sometimes it sticks, so taking off the sending unit and prying the valve back to center will solve the problem. Assuming you have good and equal hydraulic pressure in the brake system the valve remains centered and the light off. I use a spring shaped tool that holds the valve open in the center position during bleeding. This tool is cheap and available at most auto parts stores. It slips over the nipple in the combination valve (most Ford and Chrysler)and holds it open. Don’t try to do this with anything other than the tool designed for this process, you will screw up the combination valve.
William in Atlanta

 

William, do you have a picture you could post of that tool? I was looking for one for myself. I know that Ford had a special tool that replaced the switch when bleeding, but they don't carry it any more. Would the NAPA dealers carry one?

 

William, when you say remove the sending unit, is it the electronic one. I tried bleeding my lines from the rear and then from the front and still no joy...Would kind of like the system to work
Thanks

 

Sorry no picture. I will post the part number when I get home. This tool is about the size of a quarter, U shaped and acts like a spring. As for the sender/switch on the combination valve, unscrew it. Fluid will not leak out. There is a U shaped indentation in the valve that should be centered. These valves do not stick often, so be sure you are following Fords combination valve centering procedures.
William in Atlanta

 

> smaller resivoir in the front and a larger in back.

The larger in back is for the front brakes and the smaller in front are for the rear brakes.