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What proportioning valve to run?

afroman006

afroman006

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I want to put an adjustable proportioning valve on the trail truck that I am building because the brake system is completely apart already, and I am running disk brakes front and rear and want the best performance possible. My setup is a D60/14bolt with disks. I've been looking on Jegs and Summit and all their proportioning valves only have a single input and output. Now that I'm looking into it further, I realize I have no idea how to go about plumbing the brake system with the adjustable valve. I have a few trucks to look at as far as factory plumbing goes so thats not a problem, but installing the adjustable valve is. How has everyone else done it and what valve did y'all use? Here's a few links to valves I've been looking at. Thanks.

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=1178&prmenbr=361

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=1179&prmenbr=361

http://store.summitracing.com/defau...ults=false&N=0&target=egnsearch.asp&x=43&y=11
 
What you have to do is plumb those in-line with the brake line to the rear brakes. It allows you to dial down the pressure going to the rear, so that more pressure is applied to the fronts first. If you decide on going this route, you should remove the proportioning valve portion from your existing unit (I believe there is a spring and plunger that need to be removed from it), which should be mounted under the front of the truck....
 
proportioningvalve.jpg
 
The first one you linked is infinitely variable. The second one has 7 settings. Those are mostly used on race cars that get refueled during the race. The proportion is changed on the fly depending on fuel load. Detents are a good thing there. Wouldn't bother with it for typical 4x4 use.

Odds are really good that the stock prop-valve setting won't be ideal for your combo.
 
On my 78 GMC, I used a summit dial type valve, which is mounted under the truck, at the front of the passenger seat, with the dial on the inside of the cab. There were fittings in the brake lines right there, which were disconnected, and they fit right into the p-valve like it was made for it.
 
IIRC you can use a PV from a P30 Van The "Bread trucks" they have 4WD..IIRC also maybe a mid 80's model..
 
Where'd you get those linelocks? Does the line for the front brakes run through any kind of valve? Where does it split? So it sounds like only the rear brake pressure is adjusted right? Anyone know where I can find a writeup on modding the factory valve? I've read about people doing it before but I dont know how. Thanks for the help amigos.
 
afroman006 said:
Where'd you get those linelocks? Does the line for the front brakes run through any kind of valve? Where does it split? So it sounds like only the rear brake pressure is adjusted right? Anyone know where I can find a writeup on modding the factory valve? I've read about people doing it before but I dont know how. Thanks for the help amigos.
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They're Biondo Racing line locks. They cost $40 from Summit. The first two I bought cost me $30 but they raised the price a while back. I paid $40 for the one on my wheeling rig. I have two on my daily driver because I didn't want to abuse the driveline when I was winching.

The front and rear brakes run through a combination valve which is on the back side of the front crossmember on our trucks. This valve does some proportioning (not much, most is done by the piston sizes in the master cylinder) but more importantly has a safety valve in it. It has a floating piston in it. This piston "senses" (responds) to a large differential in pressure. If one side has a ton of pressure and the other side has virtually none it will trigger and slide over to shut off the flow of fluid to the low pressure side. This will allow you to have brakes the next time you put pressure on the pedal. While the master cylinder does have two channels, they require pressure in both to work.
 
Im replumbing the entire system because my trail truck was formerly a 2wd with rusted out brakelines anyway. This will allow me to position everything for maximum ease. I think I'm gonna go ahead and gut the stock valve, and install the adjustable one from Jegs in the rear. Thanks for the help guys.
 
afroman006 said:
Im replumbing the entire system because my trail truck was formerly a 2wd with rusted out brakelines anyway. This will allow me to position everything for maximum ease. I think I'm gonna go ahead and gut the stock valve, and install the adjustable one from Jegs in the rear. Thanks for the help guys.
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If you remove the stock combination valve and you lose a single brake line or hose you have no brakes. The combination valve is needed to turn off fluid flow to the blown channel so the master cylinder can work.

I replumbed my entire vehicle as well (bare frame) and ran all my lines down the driver's side but I left the combination valve in the stock location (easiest place for it, believe it or not).
 
I used a proportioning valve from a later 90s ifs series k truck 4wdb.... fittings were all the same... and that way I dont have something aftermarket.... worked well... new from gm about 75 or so

cam
 
CyberSniper said:
If you remove the stock combination valve and you lose a single brake line or hose you have no brakes. The combination valve is needed to turn off fluid flow to the blown channel so the master cylinder can work.
Click to expand...

Does the prop. valve reset itself when the problem is fixed or does it have to be done manually somehow?
 
Most will reset with a few hard jabs of the brake pedal once the problem is fixed. Otherwise you need to do it manually with a screwdriver.
 
It will still work w/o the stock CV, it will just have a lot of pedal travel if it is the front system that fails.

In normal use the rear piston 'captures' a slug of brake fluid btwn the pistons in the m/c, which drives the front piston. When the system that the rear piston is plumbed to fails (usually the fronts) the rear piston travels a short distance until it mechanically contacts the front piston, and then the rear drives the front forward.

With the stock CV in place the shuttle pin will move to close off the failed system (assuming the fail point is beyond it), which could still result in the captured slug of fluid. The first pressing of the pedal would be long, but after that it should be close to normal except that the brakes obviously won't work as well.
 
I got my linelock and proportiong valve today so I want to do the brake system tomorow but I cant figure out exactly how to modify the stock propotioning valve. I read the tech article but to me its a little vague as to the exact part that needs to be mod'd. If someone could take the following pics and draw a red circle around what needs to be done I'd really appreciate it. From what it sounds like in the article, part of the little stick needs to be broken off, but I dont know what part. Also, does just the seal need to be removed from the metering valve? Does anyone know where I can find the diagram the article keeps refering to? Thanks.
 
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