I posted this on another forum and it was recommended I try posting it here:
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I have a 1968 ford F250 pickup I have been trying to get back into shape. This weekend I re-wired the whole truck and was only left with one wire with no place to go. It seems that the truck has no pressure differential valve so there is no brake switch to plug the brake idiot light into!

It's clear from the "Detroit Irons" CD, with the manuals, I have that the primary and secondary from the master brake cylinder should go to a pressure differential valve, but it's clear from following the lines that the secondary from the master cinder goes straight to the rear drum brakes and the primary from the master cylinder goes to the metering unit that drives the front disc brakes. In fact about where the pressure differential valve goes there is some tape wrapped around the brake lines as if someone pulled the unit out and taped the brake lines together. It's right where the wire for the brake idiot light should attach to the pressure differential switch.

I am having trouble locating a replacement pressure differential valve. I've been browsing the web unsuccessfully and also stopped by one of the local junkyards to no avail.

I'd rather not insert a combination valve, which do seem to be available but would force me to redo the brake lines, which I really don't want to get into. Wouldn't mind a proportioning valve with the pressure differential valve integrated into it as well, but I haven't found one of those either.

In fact if such a thing exists I would consider upgrading to anti-lock brake system depending on price, but would prefer to keep things simple if at all possible.

Where can I find a pressure differential valve for a 1968 ford F250 ?
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Any pointers appreciated.

Thanks
Chris

 

i just went to a performance shop and got one from them. it's adjustable so when i get power brakes you can just dial it in. for now i'm just running it wide open.
gl
mark

 

Chris it sounds like someone was hacking on your F250 before you got it. Brake line from the master straight to the rear wheels isn't factory. Tape on a brake line? A fairly easy update would be to use a proportioning valve from a 73-79 truck. They have the differential valve built into them and are easy to plumb along with easy to find.

Upgrading to antilock would require a lot of work and component replacement.

The best brake upgrade I did to my ABS equipped 96 F150 was to pitch the master, control valve and module in favor of a master and prop valve from a 76 F150.

 

I dont know if you can modify it or not but i have one from a power drum truck you can have. I know its not the same as disc though.

I believe the valve should have been located inside your frame rail at the bottom of your fire wall. From what it sounds like your lines arent factory so whatever you end up with im affraid you will need to redo what you have. You can buy a new unit from any of the aftermarket suppliers.

 

Definitely someone has been dinking around with this truck in the past. The electrical system was kind of a a mess. Mostly I think to tap in to the system to add fancy sound system, but other wierd things like no neutral safety switch, so I could start this thing in drive or reverse which of course I found out the hardway in a parking lot with a big lurch when I started the truck. Luckily I didn't lurch far enough to hit the car in front of me but it was a bit of a surprise. Also I didn't have any connection to backup lights. The side marker lights never came on and fuses were popping every 2 or 3 months and the things that would go out because of the one fuse that broke weren't the things that should have been on the same fuse, At least not according to the electric diagrams that I have. That was the motivation for just doing a re-wire of the whole thing to bring it back to a known state. So, the neutral safety switch is now functional and I now have backup lights and side markers!.Yay!!!

I have a plan now and found a differential valve to put in.

Also it turned out not to be tape around the lines but a rubber brace of some kind.

I will probably add an adjustable proportioning valve to the rear line as the brakes locking up are a problem on this truck. Maybe that will help.

I'll probably put the new differential valve and proportioning valve in the lines close to the master cylinder rather then down on the frame it's easier ro get to for the instaalation as well as making it easier to get to the adjusting **** on the proportioning valve later to tweak it.

Thanks
Chris

 

C8TZ2B257B .. Brake Differential Proportioning Valve / Obsolete

Fits: 1968/72 F 100 4WD

NOS PARTS SOURCE in Lenexa KS has ONE: 913-220-5746.

DENNIS CARPENTER OBSOLETE PARTS in Concord NC has ONE: 704-786-8139.

No Ford Dealer or other obsolete parts vendor has any.
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C8TZ2B257C .. Brake Differential Proportioning Valve / Obsolete

Fits: 1968/72 F 250 4WD.

BOB ALLEN FORD in Overland Park KS has One: 800-676-0675

No other Ford Dealer or obsolete parts vendor has any.
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C8TZ2B257D .. Brake Differential Proportioning Valve / Obsolete

Fits: 1968/72 F 100 2WD / 1968/72 F 250 2WD w/Drum Brakes / 1968/72 F350 w/Drum Brakes.

No Ford Dealer or Obsolete parts vendor has any.
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C8TZ2B257G .. Brake Differential Proportioning Valve / Obsolete

Fits: 1968/72 F 250/350 w/Disc Brakes.

PEROGIE ENTERPRISES in Highstown NJ has ONE: 609-448-1684.

No Ford Dealer or other obsolete parts vendor has any.
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Some people may see the April Fools Day humor of substituting Silverado for F 100 & F 250, but I can assure you...I do not.

Looking up parts can be a PITA as it is. This just makes it more difficult without knowing what series the truck is. It also makes it difficult to proof read the text.

What bonehead at Internet Brands thought this up?