Proportion valve for a '72 - manual brakes

[Venado82]

I'm having trouble finding a replacement proportion valve for my '72 F100 custom. It's 2 wheel drive with drums on all four corners. Does anyone have any suggestions where to find one or maybe a retro fit from a later model. I can't drive it right now cause the brakes build pressure and lock up. Fortunately it's happened, the locking up, after I've parked it, never while driving although it came real close to it on Tuesday.

[FORDification]

First, if you're looking for a proportioning valve for drum brakes, that's maybe why you're not finding it. Only vehicles with front disc brakes have a proportioning valve...vehicles with 4-wheel-drums have a distribution block. It's basically nothing more than a brass 'Tee' with a built-in pressure differential switch.

You can use the ones for similar-year Mustangs, they're readily available in the aftermarket. It's the same piece.

However, based on your description of your problem, I seriously doubt it's the distribution block. The block wouldn't cause pressure to build up. However, one thing that WILL cause those symptoms, and is actually pretty common in these old trucks, is that the flexible lines to the front brakes will come apart on the inside of the line, which essentially pinches it off. You'll be able to get brake fluid past the swelling to actuate the brakes, but then the fluid can't return past the swelling to the master cylinder. Before you go spending money on buying a part you probably don't need, check those front brake lines.

[michael69]

I had same problem and it was the front rubber lines like Keith said.

[Venado82]

I've already relpaced the front lines and master cylinder. I replaced those about a month ago when this first happened and you were right the hoses were toast and the master cylinder was bleeding pressure by after I let off the pedal. So, I'll try to find the distribution block from a mustang. I've looked at the local parts stores, LMC, Nat'l Parts Depot, Dennis Carpenter,etc. The local Ford house told me that Ford discontinues the part in 1995 and none were anywhere to be found. So, maybe I'll have some luck with the Mustang part. Thanks for the info anf help.

[flyboy2610]

If it's your rear brakes locking up, remember that you have a rubber hose back there, too. It goes from the rear axle to the metal brake line, permitting the axle to move up and down.

[Venado82]

It's the front brakes. So I've ordered an aftermarket distrribution block. It'should be here next week. I'll let y'all know if it fixes my problem.Thanks for all the info and troubleshooting.

[ForingaMex]

I agree with Keith. That distribution block is most likely not your problem. Do you have a booster? If yes than here is one more thing to check. You mentioned that you replaced the master cylinder. If the push-rod between the booster and master cylinder is adjusted to far out (too long) that will cause your wheels to lock up. I know this from experience. Happened on an 83 F100, I drove to work, about 15 miles, and worked fine but when I wanted to go home...wouldn't go. I didn't have all the tools with me so what I did was loosen the the nuts that hold the master cylinder to the booster of a couple of turns and that released the brakes so I could go home and adjust it properly.

[Venado82]

No booster. Just a master cylinder and the distribution block is the only thing left in the system, on the front and that's whats locking up, that wasn't replaced when this happened about a month ago. The rear brakes are working fine but after driving it for a short distance the front brakes lock up, more so on the passenger side than the drivers side. The new distribution block should be here in a day or so. So, I'll update with the results.

Again, thanks for all the help. I really appreciate it.

[fordman]

where ever the problem is it is because of a blockage in the lines. it could be in the dirty old valve it coul dhave worked its way to the passenger brakes by now. but it does sound like a blockage in the line. and it wont return the fluid so it builds up and finally locks the brakes because the pressure won't return to the master.

[Venado82]

I got the dist. block installed and drove the truck all day. The problem appears to be fixed. Thanks for all the info; I really appreciate the help.

[dssco]

I had the same problem years ago on a truck I put together. Turned out to be the wrong brake pedal/too long of a piston rod on the master. The pedal would not come up far enough so I pushed the rod in a little. After a few stops the front brakes locked up until pressure was released on the front lines. Fixed it by putting the right pedal in.