Proportioning valve -and disk brake upgrade, please help

[57dodged100]

MY QUESTION: WILL MY STOCK PROP VALVE WORK? DO I NEED TO SWAP PROP VALVES?

Ok, I have managed to confuse myself (which is an all to common occurence). I'm working on /6 1972 Scamp and currently swapping in the Kelsey Hayes set up from a '68 Barracuda. When I bought the set up the seller included a proportioning valve from "another disk/drum car" (unknown year). The date stamp on the prop valve is 188 5 (which I think means July 7, 1975).

This prop valve looks exactly like what is on my all-drum stock Scamp. Both look like:

The '72 Manual describes this as OEM on drum cars and describes a different prop valve for disk/drum cars.

However, Muscle Car Research (https://www.musclecarresearch.com/1970-76-mopar-combo-valve-rebuild) and In-Line-Tube describe this as Mopar's prop valve for disk/drum cars. In Line Tube has reproduced and sells these as disk/drum prop valves (http://inlinetube.com/Prop Valves/BLK250.htm)

Here is the FSM diagram:

MY QUESTION: WILL MY STOCK PROP VALVE WORK? DO I NEED TO SWAP PROP VALVES?

 

[67Dart273]

Do a search. There are MANY threads on this. Over the years, "things have changed." Some cars used separate metering / hold off / prop valves.


I do not know if that valve will PROPERLY proportion the specific brake combo you are going to end up with. This is determined by the type of front brakes, IE calipers and pads, the size of the front pistons, the size of the rear brake shoes, the size of the rear cylinders, and TIRE size and differences. Example, my own car runs different tires front / rear

Your "new" valve SHOULD NOT BE the same as your 72 "all drum" "device" take a second, close GOOD look at what your 72 has.

READ this thread

http://www.forabodiesonly.com/mopar/showthread.php?t=81799


THIS is what should have originally been on an all drum car. This is NOT a proportioning valve. It IS a combination distribution block and brake failure warning switch Look CAREFULLY. This is NOT shaped the same as the one-piece prop valve / brake switch you seem to have purchased:

Look CAREFULLY at this photo from the above thread.

THIS is a distribution block / brake switch and is NOT a prop valve. This is what SHOULD be on an all-drum vehicle

 

[57dodged100]

Your "new" valve SHOULD NOT BE the same as your 72 "all drum" "device" take a second, close GOOD look at what your 72 has.

Yep, you are right again! I'm embarrassed that the correct advice was "look closer." I have the distribution block which is shaped differently. ops:

Thanks for your quick and reliable help! I bought the rebuild kit and will swap in the proportioning valve after cleaning it up.

 

[67Dart273]

Frankly, many guys on here recommend you keep your old distro block and install an aftermarket adjustable valve. Unless you exactly duplicate the brake set up that was original, and tires similar, brake front / rear bias might be off. You might be lucky

I was intending to do the same thing.......adjustable valve........But I ended up with 4 wheel disks instead, and what little I drove that setup late this summer needed no prop valve at all.

 

[Mattax]

That's an excellent thread.
Here's another one with links to lots of pictures and the set up from various years.
http://www.forabodiesonly.com/mopar/showthread.php?t=263287

If you are using a K-H setup, then you have a better shot at a great match by using a prop valve from a K-H setup than from the '73 up floating calipers. Someone could calculate if the piston areas are different and how much. But without that, the best bet is copy the factory completely. Whether its the combo valve or the two piece valve doesn't really matter.

An adjustable is always an option. its one I like but not for everyone. This means you need to tinker with it to get the fronts just locking up before the rears in the worst case situations you can come up with (safely). They also take up a little bit more room. Russel is one of the smallest. As mentioned one thing that might be different on your car than the original is the rear wheel cylinder size (and rear brake swept area when they went to the wider drums). I agree tires make some difference, but presumbly this is street use, street tires and we're not expecting the sort of weight transfer that happens in competition.

 

[383Duster]

I got luck on my Scarebird conversion and didn't have to change anything other than the master cylinder. The rears do not lock during a panic stop and I know they work from letting the car idle on my lift and applying the brakes.

 

[airgrabber]

I believe the same valve was used from at least 1970 thru 1975 on disc brake a bodies - an all brass one like in the very first picture. Around 75-76 they started phasing in a cast iron version with a different layout. I pulled the attached vale off a 75 Swinger with sliding calipers. It looks IDENTICAL to the original valve on my 70 340 Swinger with the KH 4 piston set up.

 

[AJ/FormS]

I have those K-H on my S and 10x2.5 drums on the back, 245s front,295s out back on 10inch alloys.I had to defeat the proportioning part of the valve to get the back to actually contribute to stoppage.Oh I forgot I downsized the wheel-cylinders 1/16, too.Daily driver and street bomber.Those rear brakes saved my bacon a few times. 28psi frt, 24 out back.OEM type linings. Absolutely no tendency to spin-out.