Proportioning Valve Button Stuck?

[Alex Hayley]

I have attached a picture of my proportioning valve button and am not sure if it is stuck in a depressed state. If it is stuck how do I getting it un-stuck?

[1968SWBBigBlock]

Having a stuck proportioning valve is actually very common
You have 2 choices - one is to tear it down and clean it out - you may find it so pitted inside that it is no longer usable
second choice is to buy a new unit from POL or CPP
I ended up buying a Wilwood after tearing into mine 2 or 3 times and it still would give me fits.
The Wilwoods are adjustable for front to back bias but you do loose you idiot light plug in

[oldblue1968chevy]

whats the button do anyway?

[Alex Hayley]

Good information. Thanks.

Would this be the valve you purchased? http://www.summitracing.com/parts/WI...1179/?rtype=10

Did you need to change any of the existing line fittings to hook up the new valve?

[oldblue1968chevy]

Can someone explain how the adj. vavles work, how do you know how to adjust it to what you need lol?

[RichardJ]

You guys are talking about two different kinds of valves.
The stock valve is two or more valves combined into one unit and for that reason it is called a combination valve. A combination valve includes a proportioning valve, but the part of the combination valve that includes that button is called a metering valve.

A metering valve prevents fluid from flowing to the front disc brakes until the fluid flowing to the rear brakes reaches at least 40 psi. It is sometimes called an anti-dive valve. It makes the rear brakes begin to work before the front when you have light pedal pressure so the car doesn't do a nose dive.

[1968SWBBigBlock]

I would have to look at mine to tell you if it identical but it is close.
The set up is really simple - install the valve - yes you will need to fabricate parts of a new line to adapt it into your system - I actually tool the factory mounting bracket and mounted the proportioning valve on one side and a line lock on the other.
After the valve is installed take you truck for a drive - jam on the brakes extra hard - if the rear wheels lock up turn the knob to reduce rear bias, if the rear tires do not lock up keep turning the bias up until you get the lock up and than turn the knob the other way to reduce bias

[RichardJ]

This is the typical GM combination valve. Proportion valves do not do anything until the pressure reaches a couple of hundred pounds. If you have one that begins to work at 200 psi, then when you have 200psi on the front brakes, you will have 200psi on the rears. At 300psi to the front you may get 280psi to the rear. At 1000psi to the front, you may get 700psi at the rear. The harder you press on the pedal, you get proportionally less pressure on the rear brakes than you do the fronts. Hence the name proportion valve.

[oldblue1968chevy]

so if i decided id replace my 40 year old unit, would an adj. prop. vavle be a better idea? I think summits cheaper than places like ece ccp etc