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fred56 09-14-2005 03:55 PM

proportioning valve
I am having a friendly(HaHa) discussion with my buddy about after market proportioning valves and since we don't have one handy to prove one of us wrong I thought you guys could set one of us straight.

I contend that if you turn the valve in(clockwise)that the fluid to the back brakes would be cut down. Am I right or wrong?

Thanks a lot for the help.

Canzus 09-14-2005 04:25 PM

That *is* how it works on mine, it'd probably work
the other way if you install it bass ackward...

yesgo 09-14-2005 08:03 PM

Clockwise puts more pressure on the spring. More pressure on the spring means it takes a higher psi to push the spring. The spring is pushed by fluid pressure. Therefore more pressure on the spring means a higher fluid pressure is needed to move it, resulting in more/longer action in the rear brakes before pressure is reduced. Full master cylinder pressure is allowed to the rear brakes until the piston, held by the spring, moves.

The adjustable valve has arrows on the knob. Clockwise=Increase.

Putting it in backwards would effect operation, but I dont think it would operate correctly or opposite.

fred56 09-15-2005 07:08 AM

Proportioning valve
Thanks for the info - Glad I was right.

yesgo 09-15-2005 06:36 PM

If you turn the knob out fluid is cut down. Sounds like your friend was right.

I contend that if you turn the valve in(clockwise)that the fluid to the back brakes would be cut down. Am I right or wrong?
"Rotating the adjuster knob clockwise until it is all the way in will provide full pressure delivery..."

machinestheman 12-21-2005 12:22 PM

it depends on how the valve was designed i doubt it highly that different manufacturers make the exact same part

yesgo 12-21-2005 12:37 PM

Yeah, I guess if it had left handed threads it would work the other way.

machinestheman 12-21-2005 01:20 PM


Originally Posted by yesgo
Yeah, I guess if it had left handed threads it would work the other way.

no no not at all what i was getting at if the spring is under or over the valve would change the direction in which you would have to move the valve to close/open flow and yes if it was left-handed thread it would work opposite i dont know why anything like that would be left handed but sure ill go with it

Dan B 12-21-2005 01:36 PM

1 Attachment(s)
Howdy All,

"Turning the knob clockwise (in) increases rear brake pressure" is the correct answer. I went through this exercise on my car when I first got it on the road. I thought if you unscrewed (counterclockwise) the knob that it would let more pressure to the rear wheels but I was wrong. It's a complicated explanation about the internal springs (see yesgo) but he is correct. Contrary to what seems logical, you do screw it in (clockwise) to let more pressure to the rear brakes.

Dan B.

yesgo 12-21-2005 02:36 PM

I guess it is possible to increase the spring pressure by loosening the knob, but it seems overly complicated. I am not aware of any pressure sensative prop valves like that. Adjustable and non adjustables I know of are offshoots or knock offs of a Kelsey-Hayes design put in production in the mid sixties.

The spring has to put pressure on the piston. Increased spring pressure increases the knee point=increased line pressure.

There is a brass valve being sold as a proportioning valve which works the other way. You can find it at some hot rod vendors. It looks cool, but isn't really a brake proportioning valve. It's more like a faucet. It increases or decreases flow at all times. Not designed or recommended for brakes.

47convert 12-21-2005 02:42 PM

So, if your rear brakes are locking up you would back the valve off?

yesgo 12-21-2005 02:46 PM

That is the way it is supposed to work.

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