PROPORTIONING VALVE -- 4-WHEEL DISCS

Hopefully someone can help. I've recently installed a Dr Diff 10.7" rear disc setup onto my "72 Challenger. Fronts are Cordoba 11.75" rotors and factory rebuilt new stock calipers; steel braided lines. The dash brake light stays on. I spoke with Dr Diff (Cass) and he told me the factory proportioning valve body needs to be gutted empty.. or else a replacement drum-drum proportioning valve needs to be installed (along with newly shaped lines to the master cylinder... I'm using an aluminum Mopar unit that was installed many years ago).

Basically, the rear discs are not working until I get the prop valve modified as above (gutted or replaced).

Does anyone know IF this particular factory cast iron prop valve body can be gutted? Its the later-style rounded design (possibly used late 72 through 73-74 on E-bodies). Dr Diff/Cass isn't sure if it can be modified/gutted. He can sell me a drum-drum new prop valve... along with the newly shaped brake lines... would take brief time for this to be done.

T/Anks ahead very much for any help.

I saved this picture years ago.

Get his valve and lines and you will be done with it.

I gutted the brass one on my 69 Dart, ended up just using it as a T for the front brakes and ran the line for the rear brakes directly to the master cylinder.

T/Anks a million!!! I'll decide further!!!!

T/Anks for the reply... I'll let you know what I decide.

Is it my eyes or do you have two separate wires attached to the valve?

There's a top black wire... and side/center black wire... not sure which does what, but at least one of them activates the dash brake light. The car is actually a '72 model (cloned into a T/A a long time ago... by me)

Here is the link to Dr Diff's site that he suggests to get his drum-drum prop valve (that can be used for disc-disc setups).

https://www.doctordiff.com/brake-valve.html

I have never seen or heard of a two wire valve, Maybe that's part of the light problem. That lower wire I do not believe should be there. It could be holding the valve in the wrong position. That valve end should be free to move.

So a car that originally had all drums is upgrades to disk all the way around will not need the proportioning valve changed ? Not even gutted? What master cylinder is used ? The drums one or a disk brake one?

all drum systems do not use a proportioning valve. That is handled by wheel cylinder size, shoe size, drum size or a combo of those factors. A properly setup all disc system will account for it in rotor sizing, caliper bore size, pad size or a combo of those factors.

An aftermarket all disc setup will most likely need a proportioning valve because most of them are NOT properly setup.

All that "valve" is in an all drum setup is a splitter and in some cases a brake warning light switch. To which you will most likely need to add an adjustable aftermarket proportioning valve to adjust the aftermarket all disc setup to work properly. As in the rears don't lock up first.

Nitroism -- the valve on my car is original... and there are similar others that also have the two wires.

Convex -- From what I've been learning, yes... drum-drum setups truly don't need a prop valve, same as disc-disc... no need. I wish this were in writing from vendors.

Sniper -- I believe you're correct with the info.

I've also learned that rear adjustable prop valves are more truly needed for light-weight rear-end cars... heavier cars can do away with any need for such a prop valve when brakes are same design (drum-drum or disc-disc).

Perhaps, it wouldn't hurt to have an adjustable prop valve (used only for the rear)... but the need would have to be determined by brake testing... i.e.: rear lock-up. I'll determine that as I progress with the brake swapping..... possible Wilwood front calipers.. or swap to the front Viper setup from Dr Diff.... pending how my other rims fit over the setup.

Note: My master cylinder is an aluminum Mopar unit (new) from an ~1980s pick-up... installed many years ago as a weight-savings vs the original heavy cast-iron unit.... has been A-OK for me.

I do not think that is correct. My FSM only shows one wire. I would like to see the end of that valve with the wire unplugged. To me that wire is attached to a valve end and not a switch. FSM shows one wire going from the valve to cavity 24 on the bulkhead.

I like to when I can learn from others' mistakes. I was told to just use the old Drum Drum Distribution Block and add an adjustable on the rear by an older friend who has done lots and lots of rear disk kits. To just make a cut with a tube cutter and splice one in.

There is an episode of Roadkill Garage that David Freiburger and Steve Dulcich put a rear disk kit in a car. They spent all the evening and into the night fighting the proportioning valve that came with the kit. The next day put the old Distribution Block back in with a screw-type adjustable valve spliced into the rear brake line in no time at all. they tossed the new that never worked right proportioning valve in the trash can and said they would never ever do it any other way.

This wire does not attach to this valve. Unplug it and you will see it is not a switch. Grounding it will cause the light to be on. It most likely went to another valve depending on the application. Right now it ison the end of the valves spool. Like I said unplug it and look.

Correct. The wire on the end of the prop valve is not correct. Nothing should be connected to that "pin". It needs to move in and out. Look at the exploded view. There are springs on the back side. That "pin" needs to move.

Might be worthwhile to trace both wires to see where the wrong one should go. A schematic may help as well

OR Maybe it's a developmental Hemi ABS valve, Extremely rare.