Sorry. I really can't identify the newer trucks. Maybe I'll have one someday, and start this process over again. I used to have a 79 F250 and I wish I had never given it to my son. It had the 460 in it and would get 8-10 mpg going uphill or downhill, pulling a horse trailer or empty...

I rewired my entire 51 F4 from scratch, so I'm not afraid of wiring. But I don't know anything about the 67-72 ignition switch so it kind of puts me off the whole pressure differential valve idea. I wouldn't mind including it if I knew more about what I'd have to do. But I don't want to enlarge the hole in the dash if the ignition switch is bigger. Or if the switch wiring is totally different...

And I'm pretty sure I'd also know if half of the brakes weren't working, without a light, as you said.

I'm glad I started this thread, even though I've kinda talked myself out of it.

 

Often it just helps,to use people as a sounding board. Keep,us up to date on your jalopy

 

Fixed it for you, you omitted F350 and 1968/75 F250 4WD is different.

 

Thanks Bill.

 

Where would it be located? There is a '69 in the junkyard near me.

 

I will have mine off as soon as I do my disc swap. Although I'm pretty sure it's stuck to one side so it would have to be taken apart and reset.

Have you considered a universal one? Maybe even an adjustable unit?

 

I'm just guessing here as I don't currently have one in my truck (65 F250). But I believe it will be right below the master cylinder, as both front and rear brake lines feed into it from the m/c.

 

Thanks Garrett.

To tell the truth, I never heard of the pressure differential valve until Steve mentioned it is part of the system on 67-72 trucks with 4 wheel drum brakes.

It's not a proportioning valve, which would be adjustable. It's to provide a visual warning (light) if there's a pressure difference between the two ports. And I've already got the rebuild kit info from Steve and another nice contributor on here.

PM me with what you want for the one you're removing from your truck. I can rebuild it.

 

ok.. ill take a look. I'll be there tomorrow.

 

The PDV on a Bumpside will be located inside the left frame rail, just behind the steering gear box.

 

Steve, I know you gave me a link to the wiring diagram for the Prove Out circuit, but now I can't find it. And I know you said it's wired into the ignition switch and that it checks the circuit with the key "ON". What I don't understand is how that works. Can you enlighten me?

I'm trying to figure out how to make this work (if possible) on my truck without changing the ignition switch.

 

The only adjustable proportioning valve (stand-alone Kelsey-Hayes) from the factory, that I know of, was on the '65-'67 Mustangs with factory front discs. Outside of this, I don't know of any OEM Ford disc/drum brake valves that have any adjustment means on the proportioning circuit of the valve assembly.

Outside of this, the only adjustable means would be with an aftermarket manually-adjustable proportioning valve --but, 4-wheel drums don't need proportioning so, that doesn't apply in this case.

 

 

The only proportioning valve I've ever dealt with was part of the aftermarket disc brake kit I installed on a friend's 65 Mustang to replace the front drum brakes. It required adjustment after installation, so I made the false assumption that all proportioning valves are adjustable.

 

The only reason to use the diff-pressure valve (really just a switch) is to light a warning light on the dash and get ticked off every time you bleed the brakes because you have to re-center it. Honestly, I would not add one just because you are going with a dual MC. The proportioning valve is only necessary when you have a disc/drum setup. Drum/Drum does not need one. And the adjustable Mustang unit was 65/66 KH. In 67, they used a fixed cylindrical prop valve cleverly located at the rear axle up under the car. In 68/69, they made it mount to the same bracket as the diff-press. In 70 they made an integrated unit. I would just plumb direct. The diff-press switch does not buy you any performance in the braking system.