Proportioning Valve?

Hi everyone!
I'm new to the group and recently bought a '57 210. I am going to re-do the brakes, it has been updated to power discs in front, It has a proportioning valve( so I'm told) what is it?, should I do anything different when changing the front brakes?
Thanks fro any advice/giudance you can give. Have a great day!
-Mack

Welcome Mack - A proportioning valve controls the rate of pressure build-up to the rear brakes thus, preventing the rear brakes from locking up. There are two types adjustable & non adj.
Usually when the vehicle is upgraded to front disc brakes the proportioning valve is used from the donor car.The valving is proportional to the wt. bias of the car......Don

Here ya go Mack.
Don is correct, the one most frequently used on your type of conversion looks like the gold one, upper right. Usually mounted near the master cylinder (sometimes referred to as a combination valve).
The most typical aftermarket, adjustable type is the lower right, usually mounted in the line to the rear brakes.

I much prefer the adjustable proportioning valve, lower right in Bob's pic. Looks like a Wilwood, lots of companies make them. The adjustable valves in the rear lines work great for me, one more way to tune and tweak my ride to work the way I want it to.

Some GM's, like my truck, don't use a proportioning valve with the disc/drum setup. Instead, you get a pressure differential switch. What that means is if there is a pressure difference between the front and rear brake systems -they are seperate, sealed systems- a plunger will move, completing the circuit to the big light in the dash that says brake. That means one of the brakings systems has failed and you should start trying to get the truck slowed down. The switch has no function in regards to stopping the vehicle. So, you may not even need a proportioning valve -you surely don't need the pressure differential switch.

Thanks Guys for the info! Should I do anything differently when I go to bleed the lines?
-Mack:3dSMILE: