PROPORTIONING VALVE -- 4-WHEEL DISC BRAKES

[Mopar Mitch]

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.

 

[moparleo]

I would spend a few dollars and get the one that Dr. Diff sells.
If it will work for sure why take a chance that the one you have won't and you end up buying the recommended one anyway.
You have more recourse if there is a problem if you get it from a company.

 

[Challenger RTA]

Do the brakes pump up and is parking brake working correctly? Four wheel disk bakes require a larger volume of fluid. hence a large bore master cylinder. Did he say any thing about the residual valve in the master cylinder for the rear brakes. I think it has to be removed? don't do it unless you know for sure! Did they also say to put an adjustable proportion valve for the rear?

 

[70chall440]

First off Cass knows what he is talking about, but the reason your brake light is on is because the valve in the P valve is stuck in one direction. Since the rear brakes are not working I'd say it is stuck on that circuit.

When I do 4WDB systems I used a disc/disc P valve such as this one; Proportioning and Combination Valve, AC Delco 172-1353 and 172-1361 Type

Are these power or manual? Whatever it is you need to match the MC to the system. Typically I use 1" bore MC for power and a 1 1/8 for manual.

 

[DaveBob]

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.

View attachment 84021

Here is a picture from the 1970 factory manual, showing the location of the proportioning valve, and a picture of the distribution block / metering valve I bought from Dr. Diff. The only problem I had with the Dr. Diff part is leakage between the two parts that comprise the larger brass block.

 

[Mopar Mitch]

Do the brakes pump up and is parking brake working correctly? Four wheel disk bakes require a larger volume of fluid. hence a large bore master cylinder. Did he say any thing about the residual valve in the master cylinder for the rear brakes. I think it has to be removed? don't do it unless you know for sure! Did they also say to put an adjustable proportion valve for the rear?

Bleeding of brakes 3- times gave a nice hard pedal... no air bubbles.

Parting brake works properly.

Cass advised me about the Residual valve... I checked the master cylinder (Mopar aluminum from ~80's truck)... not present.

Rear adjustable prop valve typical for "light-weight rear" cars... I'll determine later if needed after testing for rear lock-up.

 

[Mopar Mitch]

First off Cass knows what he is talking about, but the reason your brake light is on is because the valve in the P valve is stuck in one direction. Since the rear brakes are not working I'd say it is stuck on that circuit.

When I do 4WDB systems I used a disc/disc P valve such as this one; Proportioning and Combination Valve, AC Delco 172-1353 and 172-1361 Type

Are these power or manual? Whatever it is you need to match the MC to the system. Typically I use 1" bore MC for power and a 1 1/8 for manual.

70chall440 -- these are power brakes.

I observed that the dash brake light would go off only upon hard braking... then go back on after brake pedal released. However, I believe the rear new discs were not working (or barely at all)... as I did drive the car over the weekend to an event.

Master cylinder is aluminum.. been on for many years ... new from Mopar.. about mid-80s truck model. I forget the bore size... but its been A-OK for me.

Cass/Dr Diff advised to me that until I get the prop valve gutted or changed, the rear discs will barely be functional... and the brake light will remain on until then.

 

[70chall440]

Mitch - gotcha, are you going to gut the P valve? I would give it a try and see what happens.

 

[Mopar Nut]

Cass/Dr Diff advised to me that until I get the prop valve gutted or changed, the rear discs will barely be functional... and the brake light will remain on until then.

This is exactly what I did after installing 4 wheel disc brakes. Works great while retaining the factory look.

 

[Mopar Mitch]

I intend to gut the existing valve body... as this way I can re-use the existing factory lines.

 

[Mopar Mitch]

This is exactly what I did after installing 4 wheel disc brakes. Works great while retaining the factory look.

Did you additionally install an aftermarket proportioning valve (for the rear brakes)? At this point I wasn't planning to install one.... just gut the factory unit and reassemble the existing lines, bleed the brakes again, and hope all works a-ok.

 

[Mopar Nut]

Did you additionally install an aftermarket proportioning valve (for the rear brakes)? At this point I wasn't planning to install one.... just gut the factory unit and reassemble the existing lines, bleed the brakes again, and hope all works a-ok.

Yes I did, adjustable one.

 

[Mopar Mitch]

Yes I did, adjustable one.

Thanks.... where did you install the adjustable prop valve.. what kind/brand.. picture? T/Anks ahead much.

 

[Mopar Nut]

Thanks.... where did you install the adjustable prop valve.. what kind/brand.. picture? T/Anks ahead much.

Right after the distribution block on the frame. Brand is Baer. I have pictures on my home PC I’ll get posted.

 

[Mopar Mitch]

Right after the distribution block on the frame. Brand is Baer. I have pictures on my home PC I’ll get posted.

T/Anks very very much.... picture will help. I'm trying to rebuild and gut an extra distribution block that I picked up at the recent Colombus Mopar Nats.. although a bit cruddy, I've ben able to sandblast it nice and clean and take most of it apart... except for the internal brass valves... the bottom one is a face seating unit for the lower brake line and it has to come out... but seems stuck unless I drill it out... then ream clean the internals... then reassemble the caps as needed. BUT... that bottom brass valve has to be reinstalled... not sure if a a replacement piece is available.

 

[Mopar Mitch]

My thought was to simply to do a swap of a gutted unit and be able to reuse the existing lines... than add an adjustable proportioning valve.

I could take apart my existing unit from the car and hope that no disassembly/gutting problems would occur.