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Can a proportioning valve be recentered?

Paul_G

Paul_G

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1973 Charger. The electrical switch on the proportioning valve is closed turning on the brake warning light. Removed the switch and it checks good, toggles from open to closed when plunger is depressed. Looking through the switch hole I can see the spool, and it is off center. Is there any way to get it back in the middle where it should be?

I am rebuilding the entire brake system. Everything is new except the proportioning valve.
 
google muscle car research LLC they have tech articles on the combo valve and it appears they sell all the o rings and such
 
^^^ This.

All I can add is to make sure the valve actually will move back and forth with compressed air. I had one that took several pumps to get straightedges out but eventually it re-centered.
 
Rebuild it. Only then will you be able to see if there are any internal problems. 73 prop valves are made of steel, not brass so it could have pitting inside.
 
Paul_G said:
Is there any way to get it back in the middle where it should be?
Click to expand...
I believe, once the valve is toggled, you have to 'manually' center it. It's more like a safety valve, that shuts off front, or rear brakes, once something (low fluid) comes into play.
 
I had to recenter the one on my 70 Bee

Don't remember how but I remember having to look it up.
 
I have not manually re-centered one yet. There is a retainer that keeps them from going over center if you know it will and want to keep the line open.
 
If you needed to recenter it manually, every time you bled front or back brakes it would shuttle to one side each time you opened a bleeder screw and stay there. It doesn't!
 
dadsbee said:
If you needed to recenter it manually, every time you bled front or back brakes it would shuttle to one side each time you opened a bleeder screw and stay there. It doesn't!
Click to expand...
Even while bleeding brakes the portioning valve has pressure on it unless the reservoir runs dry. Try it sometime and see if it works.
 
I'm the one agreeing with you that they don't need to be manually centered. Crack a bleeder on one end of the car and while there is still pressure on the other it will shuttle the valve and turn the light on. I still have air in one end of the birds brakes right now as going full pedal pops the light and then immediately off when you get off the pedal.
 
did the OP push "the button"?

IIRC when the shuttle valve goes too far it causes the light switch to stay on.

I think the button resets that.

If I'm totally wrong it's because my memory from 30 years ago is foggy
 
69L48Z27 said:
^^^ This.

All I can add is to make sure the valve actually will move back and forth with compressed air. I had one that took several pumps to get straightedges out but eventually it re-centered.
Click to expand...
Compressed air did nothing. It would not move with 120PSI.

YY1 said:
did the OP push "the button"?

IIRC when the shuttle valve goes too far it causes the light switch to stay on.

I think the button resets that.

If I'm totally wrong it's because my memory from 30 years ago is foggy
Click to expand...

The little button did nothing. Dont know it's purpose, if it has one.

But I did get it re-centered. I had to get serious on brake pedal. It took several hard "stab & hold" attempts on the brake pedal with the engine running to get the spool to move back to center.

The spool was moved to the rear blocking fluid flow to the rear brakes. I think the problem was with the old master cylinder since there were no fluid leaks anywhere. If the master was putting out lower pressure to the rear side, the front side having higher pressure would push the spool over toward the rear assuming a rear brake system fluid leak/loss, or a bad MC.

To make the spool move forward toward the front side of the PV I loosened the line on the PV that comes from the front brakes side of the master cylinder. Wrapped a rag around the loosened fitting to contain the spraying fluid, then went inside the car and stabbed at the brake pedal. Each time the spool moved forward a hair. Took several hard stabs at the brake pedal to get it back.

No brake light now, but has a low pedal. Need to bleed out the brakes again.
 
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