Proportion Valve Blues

[Dyn Blin]

I'm hoping for some wisdom for this head-scratch:

The dash brake warning lamp has been lit since I purchased my truck last month. The seller represented it was a malfunctioning emergency brake switch. About a week ago, I found there is no switch triggering an e-brake warning, none were fitted for a few model years after mine.

I disconnected the switch to the proportioning valve, and the light went out.

In reviewing the factory service manual, it says to reset by pulling on the rod from the front of the valve to re-balance. Well, I pulled on it with vice-grips, and it wouldn't move more than a 1/4 inch in either direction.

The Haynes manual says to crack the outgoing lines from the master-cylinder to the valve (one at a time), then have someone put steady pressure on the brake pedal until the light goes out, then re-tighten. After trying both lines, the light remains on.

I can see the rod moving as the pedal is pumped (that same 1/4 inch), so it appears it's not frozen.

(I also check all 4 brakes for function, and all seem to be working normally.)

Any ideas from the voices of experience here?

Here's the view below the master cylinder looking from the radiator. The little nub/rod is what the manual says to pull to re-balance the valve...

 

[Gary Lewis]

While it is frequently called a “proportioning valve”, Ford calls it a “dual brake warning switch”. Basically, if you don’t have pressure in both the front and rear brake systems the shuttle is pushed one way or the other and the switch closes and lights the light. The 1981 EVTM says “check for a faulty switch” if the warning is on and the systems are normal.

I had a similar problem to yours and read in the shop manual that you should “stand on” the brakes to balance things. I did that, and several other things, to no avail. I finally replaced it with a used switch and the problem was solved. The EVTM was right. 😳

[Dyn Blin]

While it is frequently called a “proportioning valve”, Ford calls it a “dual brake warning switch”. Basically, if you don’t have pressure in both the front and rear brake systems the shuttle is pushed one way or the other and the switch closes and lights the light. The 1981 EVTM says “check for a faulty switch” if the warning is on and the systems are normal.

I had a similar problem to yours and read in the shop manual that you should “stand on” the brakes to balance things. I did that, and several other things, to no avail. I finally replaced it with a used switch and the problem was solved. The EVTM was right. 😳

Thanks Gary. I'll head to the local Pick & Pull and see what may present itself. Would you happen to know what years utilized this system?

In looking at other resources, it appears these were used prior to the '80 model year, but I can't determine the full range of model years using this component.

[ArdWrknTrk]

While it is frequently called a “proportioning valve”, Ford calls it a “dual brake warning switch”. Basically, if you don’t have pressure in both the front and rear brake systems the shuttle is pushed one way or the other and the switch closes and lights the light. The 1981 EVTM says “check for a faulty switch” if the warning is on and the systems are normal.

I had a similar problem to yours and read in the shop manual that you should “stand on” the brakes to balance things. I did that, and several other things, to no avail. I finally replaced it with a used switch and the problem was solved. The EVTM was right. 😳

I know Chris has said some valves push and some valves pull to refill an empty system.

From the sectional view of one of these things it looks like there's a spring loaded ball (like an oil pressure bypass) that will hold the spool to one side, closing off the faulty circuit.

If the fluid was old and dirty I could definitely see it getting crudded up inside.

 

[Gary Lewis]

Thanks Gary. I'll head to the local Pick & Pull and see what may present itself. Would you happen to know what years utilized this system?

In looking at other resources, it appears these were used prior to the '80 model year, but I can't determine the full range of model years using this component.

I don’t have the info as to what years have the same valve on the website, and I’m not at home at the moment and can’t get to it. But maybe I can tomorrow and answer the question. Sorry.

[PetesPonies]

I don’t have the info as to what years have the same valve on the website, and I’m not at home at the moment and can’t get to it. But maybe I can tomorrow and answer the question. Sorry.

The proportioning valve is part of the combination valve. The proportioning valve controls pressure to the rear brakes, typically when a disc/drum setup is used. But adjustable ones can be used in any situation to fine tune the brake bias. The brake light you are seeing is because the shuttle valve inside has moved to one side and made electrical contact, completing the light circuit. It moves to one side or another depending on where the loss of brake pressure was. Once everything is fixed in the brake system, sometimes the shuttle will recenter itself, but many times you need to do it. You do that by opening the brake line on the opposite end of where the problem was. So if there was a front brake problem, you need to open the rear brake fluid pressure, to allow the shuttle to move in that direction. You crack the bleeder just a tad, very little. Go inside the truck and push on the brake pedal until the light goes out. Then have the bleeder tightened back up.

[Dyn Blin]

Thanks all.

I'm going to try to "crack & balance" again with a little more enthusiastic pressure on the pedal. I'm at a bit of a disadvantage in not knowing what side caused the issue originally, but from what I read, one side doesn't suffer if it's "wrong" before going to the other, but my guess is that it's not a mechanical issue with the shuttle/piston.

No love at the pick-n-pull yesterday. I did find a switch, but it was cracked, I may try to swap it and see if it works anyway.

I'll post back this weekend when I get in there again. I may take the opportunity to do a full fluid swap and bleed before so I don't stick the shuttle trying to "fix" something else.

[PetesPonies]

Thanks all.

I'm going to try to "crack & balance" again with a little more enthusiastic pressure on the pedal. I'm at a bit of a disadvantage in not knowing what side caused the issue originally, but from what I read, one side doesn't suffer if it's "wrong" before going to the other, but my guess is that it's not a mechanical issue with the shuttle/piston.

No love at the pick-n-pull yesterday. I did find a switch, but it was cracked, I may try to swap it and see if it works anyway.

I'll post back this weekend when I get in there again. I may take the opportunity to do a full fluid swap and bleed before so I don't stick the shuttle trying to "fix" something else.

You need a partner. If you crack the bleeder, then press the pedal to move the shuttle,. once the light goes out, you don't want to release the pedal to draw some air in. You want the bleeder tightened before releasing the pedal.

[myrl883]

You need a partner. If you crack the bleeder, then press the pedal to move the shuttle,. once the light goes out, you don't want to release the pedal to draw some air in. You want the bleeder tightened before releasing the pedal.

And... If you do need the switch, they're still available from your friendly Ford dealer.

[Dyn Blin]

Our pick & pull had a new arrival, an 83 F150 with a matching valve. I managed to get the valve home- the bolts securing it to the bracket were the toughest part to let go.

I'm out of daylight today, so i'll post back if I have success next weekend. I'll try swapping switches first before I change the whole valve.