Proportioning valve

[Minkota]

What is the correct way to reset this type of proportioning valve. It does not have a reset button like the ones I’ve seen before.
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[Big Kev-O]

Originally Posted by Minkota

What is the correct way to reset this type of proportioning valve. It does not have a reset button like the ones I’ve seen before.
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Looks like you have drum brakes, right? That distribution block doesn’t have a reset. It should center itself when there is equal pressure on the front and rear lines. If the breaks have been bled and there are no leaks or air in the system it should center itself and unground the switch.
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[RichardJ]

>>It does not have a reset button like the ones I’ve seen<<

You've never seen one with a reset button. You have seen a Combination Valve that had a Metering Valve on the one end that was plumbed to the front disc brakes. The Metering Valve is not part of the Pressure Differential Switch and is not connected to it internally. The Switch, the Metering Valve and the Proportioning Valve function independently from one another. They are simply Combined into and share the one single housing.

The Pressure Differential Switch shown above, is a ON-OFF-ON switch.
You must temporarily reduce the pressure on one side in order to have the pressure on the other side push the piston in the switch back to the center or OFF position.

By side, I mean front vs rear. The difficulty is knowing if the piston has been pushed forward or back.

Have an assistant push the brake pedal with moderate pressure while you crack either a front or rear bleeder screw. A hose should be attached so that air doesn't get sucked back into the system.
If the light stays ON, go to the other end and try again. The assistant must not push so hard, that he doesn't push the piston back through the switch to the other end. The light may only flicker and he not realize what has happened.

Unequal pressure moved the switch in the first place. The Differential Switch is designed so that Equal Pressure does not move it.

Having said all of the above, some guys have had some luck, removing the switch and using a small pick, nudge the piston into the center position.

[Minkota]

Originally Posted by Big Kev-O

If the breaks have been bled and there are no leaks or air in the system it should center itself and unground the switch.
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I am unable to bleed the brakes because the valve is closed on rear side.

[Minkota]

Originally Posted by Big Kev-O

Looks like you have drum brakes, right?

The truck has disc on front, drum on rear.

[RichardJ]

>>I am unable to bleed the brakes because the valve is closed on rear side.<<

Crack open the fitting on the frame side of the rear flex line and see if fluid can't be pushed out of there.

[Jason Banks]

RichardJ has a great suggestion. My original hose at the rear axle was blocked and would not allow fluid to pass...

[Minkota]

Originally Posted by RichardJ

>>I am unable to bleed the brakes because the valve is closed on rear side.<<

Crack open the fitting on the frame side of the rear flex line and see if fluid can't be pushed out of there.

The steel brake line was just replaced due to the old one blowing. When I replaced the steel line I replaced the rubber hose so all brake lines from front of cab to rear are new.
When the line popped it moved the shuttle valve foreword (as is it’s design) so now I have only front brakes until I can reset the valve. No fluid is going to the rears.

[Stocker]

Have you tried pressing on the brake pedal very hard? That's supposed to center the prop valve piston, at least in some cases.

[RichardJ]

>>When the line popped it moved the shuttle valve foreword (as is it’s design) so now I have only front brakes until I can reset the valve. No fluid is going to the rears.<<

If you "popped" the rear line, the pressure on the front side would push the switch piston rearward not forward.

What bleeding method are you using?

[68 P.O.S.]

Originally Posted by Minkota

The truck has disc on front, drum on rear.

You have the wrong valve for disc/drum brakes. Disc/drum uses a combination valve, while drum/drum uses the distribution block you have.

Replace it with a combo valve like this https://www.summitracing.com/parts/m...ckup/year/1972

Or a proportioning valve like this https://www.summitracing.com/parts/sum-g3906

[Minkota]

Originally Posted by 68 P.O.S.

You have the wrong valve for disc/drum brakes. Disc/drum uses a combination valve, while drum/drum uses the distribution block you have.

Replace it with a combo valve like this https://www.summitracing.com/parts/m...ckup/year/1972

Or a proportioning valve like this https://www.summitracing.com/parts/sum-g3906

I have never installed one before. My current system has 2 lines in, and 2 lines out. The first one you linked has 2 lines in and 1 line out. The second has 2 lines in and 3 lines out.

[68 P.O.S.]

Originally Posted by Minkota

I have never installed one before. My current system has 2 lines in, and 2 lines out. The first one you linked has 2 lines in and 1 line out. The second has 2 lines in and 3 lines out.

Both valves I linked are actually 2 inlet, 3 outlet. You will need to plug one of the front outlet ports with a plug like this: https://www.summitracing.com/parts/leb-pl3824