Proportioning Valve Question

[GatorBate]

I want to replace my proportion Valve to see if that will improve my brakes. None of the part stores can find one for my jeep. Moriss 4x4 has several listed including what they call an upgrade to a GM proportion valve. So, what makes it better than the original part and what would I ask for (model, year,ect.) if I go to a local part store to get the GM part.

 

[thiswontbetooexpensive]

Call Inline Tube and they should be able to set you up. Local Parts Store should be able to as well. Just give them make, model, manual or power brakes, disk and drum information.

 

[GatorBate]

Been to Carquest, Auto Zone, Napa, and O'Reilly. None of them have a listing for this part. that is why I was hoping someone might know about this GM upgrade part. Maybe I could have them look for that instead.

 

[Torxhead]

I bought a reman one made by Crown for my '86 and it did make an improvement with my oem brakes. It leaked at first thru the metering valve, but that went away eventually. I did disasemble the original unit and it was quite clean inside with no apparent signs of anything worn out. I purchased it thru a local Four Wheel Parts Wholesalers.

 

[73CJ]

Concidered rear discs?

Not that hard to do and REALLY makes a difference.

 

[PaRenegade]

Try the Jeep guy Brakes
or as was said, Inline Tube Proportioning Valves

 

[GatorBate]

Thanks Guys, I finely had time to check out Inline tubing site. So if I'm understanding it correctly the proportion valve is just a safety feature that warns you of brake problems and allows the front or rear to keep working if one of them fail. It has very little to do with regulating pressure.

 

[BusaDave9]

Thanks Guys, I finely had time to check out Inline tubing site. So if I'm understanding it correctly the proportion valve is just a safety feature that warns you of brake problems and allows the front or rear to keep working if one of them fail. It has very little to do with regulating pressure.

True, and they almost never go bad.

 

[PaRenegade]

It is my understanding that they do "regulate pressure" when it's a drum and disc combo. Is that wrong?

 

[BusaDave9]

It is my understanding that they do "regulate pressure"

That is correct to a certain point.
The master cylinder applies more pressure to the front brakes. That is where the difference in pressure comes from. Disk brakes need more pressure than drums so the master cylinder and proportioning valve are different.
The proportioning valve verifies that the front and rear brakes have the correct proportioning of pressure. If the front has too little pressure (or the rear) then a plunger in the proportioning valve slides to one side. This causes the switch to activate and the brake light comes on. This also limits some of the pressure going on the strong side. So if your master cylinder goes out the proportioning valve may try to apply some pressure to the other side but it won't make a big difference. Your brake light will come on and your pedal will go almost to the floor. You will come to a stop but you heart will be beating faster because you would know there's something wrong with the brakes. It's really the master cylinder that does the proportioning of the brake pressure. Back in the '30s before the master cylinder had 2 chambers then if ANY brake line or seal went out then you would loose ALL braking.

So if you are swapping in disk brakes you really should also change the master cylinder and proportioning valve.


EDIT: did some googleing. Check out these links:
http://en.wikipedia.org/wiki/Proportioning_valve
http://www.wilwood.com/MasterCylinders/MasterCylinderValves.aspx
http://www.jegs.com/c/Brakes-Drivetrain_Proportioning-Valves-and-Balance-Bars/10165/10002/-1

A Proportioning Valve is installed in the rear brake line and allows you to adjust the rate of pressure rise to the back brakes. With an adjustable proportioning valve, you can slow down the pressure rise that occurs when you apply the brakes. Under braking, most vehicles transfer more weight to the front wheels. When this happens, the rear wheels lose some weight and can lock up if the pressure is too great too quickly in the braking process. Eventually full pressure is applied to the rear brakes through the proportioning valve.

A proportioning valve can only reduce pressure on one line (front or rear). And even then only up to a point. Once the spring loaded valve is all the way one way full pressure is applied. So the proportioning valve can never INCREASE pressure to a failing brake system.