What's up with these different brake proportioning valves?

[72farmer]

I am in the middle of converting my 67 front drums to discs.I also have a 72 c-10 that I am working on and it is almost finished.I have a 72 GMC parts truck that I have been robbing steering and brake parts off of.
I have a new master cylinder from Advance that I am going to mount on my old booster on my 67.I robbed the pro. valve off of the GMC parts truck to use on 67 and compared it to my almost finished 72 Chevy.The two 72's are completely different.The 72 GMC valve is laying on top of the 72 Chevy master cylinder in pics.What is the differences in the 2 valves?

[RichardJ]

Neither one is a proportioning valve.

The one sitting on top is a Combination Valve. The rear section of that valve contains a proportioning valve. The front section is a Metering Valve. The middle section is a switch for a dash light to indicate a failure in either the front or the rear brakes.

What you have mounted is simply a switch for that same brake failure light and is used with drum/drum brakes.

[72farmer]

So will the combination valve work or do I need a proportioning valve on my 67 disc brake conversion?

[leftybass209]

Yes, they are technically called combination valves. Alternators are actually AC generators and NOT alternators, just like Vice Grips is a brand of locking pliers. The point is, if you understand what he's saying or not.

The valve you have on top is sure to work correctly, as there were never rear disc brakes in 1972 C-series trucks. The valve that is already attached, looks like a valve from an 80's or newer Camaro, C1500, etc.... so those had both disc/drum, and 4 wheel disc options, or from a 4 wheel drum brake truck. You would need to be sure it came from something with drum brakes on the rear.

The valve on top is also getting a little harder to find in good shape, and is a much better quality when compared to the new brass prop valves that are sold.

[FirstOwner69]

The one on top looks like what was supplied with the front disc brake equipped trucks in 1971 and 1972. I have always heard it referred to as a proportioning valve. The one mounted, which I've usually heard referred to as a distribution block, was used on the 1967-1970 drum/drum trucks. I would not use the distribution block with discs.

[RichardJ]

In the late '60 some GM cars with disc/drum came with these three items.

The item in the top left is a warning switch. You can call it a distribution block, but if you didn't want the switch, the F & R brake lines can be connected directly into the MC.

The item in the top right is a proportioning valve used by GM and Mopar. It is non-adjustable, meaning the proportioning ratio is fixed. Aftermarket, stand-alone proportioning valves are almost always adjustable.

The item in the bottom is a Metering Valve or sometimes called a stand-off valve. Some vehicles are prone to nose diving with light brake pressure, at low speeds. This valve keeps your teeth off the steering wheel.

The other image is a combination of all three, hence the name Combination Valve.

[swamp rat]

If you have one for a 72 it will do what ya need on the 67.