Recentering brake differential/ proportioning valve

[TonyC]

It's actually not a proportioning valve; that is a different valve with a different purpose. The valve in question is a pressure-differential valve, with the sole purpose of triggering the warning light. I explained what the issue was–i.e., the design flaw–with that valve in an earlier post on this thread.

You said you bled the brakes at all four corners, which leads me to presume you had a chance to check for any fluid leaks at each brake and at the master cylinder, and you aren't losing any fluid anywhere. If the brakes are fully sealed and leak-free, then that differential valve should be inconsequential even if it triggers the light while you're driving. It at least was designed so as not to obstruct fluid flow if shifted to one end or the other of its travel. It's just the headache of that bright red light crying wolf on you.

---Tony

[BobCT]

Yes, I bled all four and no leaks (and at least 100 pumps to stress test the system while bleeding). On last question, does the light only come on when starting or IGN on? I've only had the car about a week and know that I've seen the light but can't recall if it was initial starting or just with the key ON. The light is not coming on now with just the key. I'm probably another week before it's running again.

thanks

[TonyC]

If memory serves from what I read, the "BRAKES" light will come on when the key is turned to the "START" position to test the circuit, along with the "HOT" light; both should turn off when the key is released if the respective systems are in order. If the "BRAKES" light stays on after releasing the key, then the piston that triggers the light switch is off-center.

My car doesn't have a brake warning light; they weren't fitted on cars until '67. Though I retrofitted '67 valves into my car, I never fitted a warning light...which is academic for me, because I know the differential piston is stuck off-center, so it would always be on. If I could disassemble that valve and install springs in it, I would.

---Tony

[brkdncr]

I’m planning to get this tool for my F250. Maybe it works on Lincolns:

https://www.musclecarresearch.com/brake-valve-tool

[TonyC]

Well...look at that! Looks like a business had exactly the same idea I had years ago but didn't quite complete! I can't quite remember the dimensions of the bolt I used in my diff valve; but if the specs for this block are the same as the brake-light switch, then it will work perfectly! And $10 is a very nice price! Thank you for sharing that link!

---Tony

[Dan Szwarc]

I have the plastic version of this for my aftermarket combination valve. I don’t think this is anything new. I’m guessing that it’s existed since the 70s.

[TonyC]

Maybe longer; the differential valve blocks had to have been concocted in the '60s when split hydraulics were adopted. I'm sure they were still used in the '70s even after springs were installed in the valves, at least as a redundant practice. But finding one today is not easy, and those one does find are Chi-Comm repros with metric measurements, mainly designed for GM cars and trucks. I got one, and it couldn't be made to work on Frankenstein. I think it's easier to cobble one up with a bolt, a dowel, and a drill.

---Tony