1968 continental proportioning valve

[Cole1968]

I'm looking for info on how to properly recenter the shuttle on the proportion valve. Any advice would be appreciated never done it before.

[TonyC]

I'm guessing you actually mean the pressure-differential valve, the one that triggers the switch to the warning light? That's usually different from the proportioning valve, which evens out fluid pressure between the front and rear brakes. I'm not exactly familiar with the '68 design, except that it was different from the '67 design; I want to say that the engineers managed to design a single multi-purpose mechanism that handled metering, proportioning, and pressure-differential warning from one unit, as opposed to the '67 setup that had separate valve mechanisms in separate locations. But I also want to say that they had not yet developed a self-centering differential; and if you have trouble with your warning light still being on, that confirms that they didn't.

Re-centering the differential in such a case is tricky and even frustrating. It involves bleeding the brakes, first on one end and then the other, until the light goes out...and hoping it stays out (the shop manual does have those instructions in it, at least the '67 edition does). But if it's been a long-enough time, the differential will likely stay that way no matter how much bleeding you do, the piston having seized in place...and you cannot even tell in which direction or side it seized at. This is also one of the frustrations of the '67 models. The only good thing is that the differential piston will not choke off fluid to the side it's jammed at, because it's not designed to do that. It's just that annoying red light that will stay perpetually on until the bulb burns out or you unplug the wire to the warning switch screwed into the differential.

There used to be a neat little device used in-house back in the day to keep that piston in center position once set to center, to keep it from shifting on its own during repairs to the brakes. It was called a switch lock, and it screwed into place where the switch would go. When engineers improved the design of the differential with internal springs, such a lock became obsolete, and it's virtually impossible to find one nowadays. However, I did figure how to cobble one up, with pieces found at the local hardware store: With a bolt that has the same size and thread pitch as the switch, and a small roll or dowel pin of the same thickness as the switch's plunger, I created a locking device that could perform the job of holding the piston down in place once centered. But, of course, being unable to un-seize the piston from its off-center placement, I couldn't use it. I do still have it, though, in place in the differential valve, lightly tightened to keep it in place and to keep the bore clean; the switch itself is stashed away somewhere. Now, Frankenstein does not have a warning light for the brakes; no Lincoln before '67 does. But I had an idea of adding an aftermarket warning light somewhere to the dash if I got that switch centered, which I never did, forcing me to shelve that idea as well.

I had wanted to try and do an upgrade mod to my differential valve, inserting springs on either side of the piston, to make it self-centering; but my valve is jammed too far inward to remove or even move with bleeding, so it's hopeless. But I don't have any deficiency of braking power from either front or rear. I think the only solution would be to install a new, modern combination valve to fix the red-light syndrome.

--Tony

[Dan Szwarc]

https://tomsoffroad.com/pages/ford-bron ... djustment/

Works for most Lincolns.

[Cole1968]

Thank you for the in depth response it helps quite a bit more than you think. My brake system does still have the separate differential valve/ metering valve, after what you have said I might just leave it alone for the time being and try to re-center it later since it doesn't completely cut off the flow of fluid for the brakes.