brake valve 1970 roadrunner

[rm6p]

I replaced the manual drum brakes with power front disc on my 1970 roadrunner. Not wanting to stray far from Ma Mopar's engineers, I used stock 1970 everything except for stainless steel brake lines and reproduction brake valves. The metering and combination valves are listed as stock for this year (late 1970) and model. I am on my 3rd combination distribution/proportioning valve. First leaked terribly. The second had no pressure coming out of the valve rear brake line port. The rear master cylinder line shot like a fire hose when disconnected from the incoming valve port, but nothing out of the rear output valve port. Third seemed to have fluid coming out of the rear port but the brake light is on and there is no rear brake action. I am thinking the plunger in the valve moved and is blocking the rear output port. I have tried stabbing the brakes hard numerous times to reset but, no luck. The service manual tells how to test the light by opening a wheel cylinder to simulate a broken line but, it does not tell how to reset the valve switch once you have tested it. Does anyone know another way to reset the valve to open all ports and turn off the brake light, or am I doomed to a fourth valve?
Thank you,

 

[Ron of Chicago]

I have always had good luck by just opening the line to the side that has the pressure as it will act like a leak and the pressure should slide the valve back to the neutral position. If not then you can try this: Set up one front wheel and one rear wheel for bleeding at the same time. Crack both bleeder screws and gently pump the pedal a few times.
The blocked side will trickle fluid out when the bleeder screw is cracked and the pedal pressed. An unblocked line will squirt fluid out the bleeder.
The lines that are clear must be left open and the blocked lines should have the bleeder screws tight to cause pressure to build up on that side. Be sure to use the standard bleeding procedures to prevent air from entering the system.
Slowly press the pedal with steady pressure a number of times until the light goes out; this will center the differential valve. You may also hear a pop come from the proportioning valve. This is the metering valve returning to its equalized position. When the light goes out, close the bleeder screw.

I hope it works for you.
Ron

 

[rm6p]

I will give it a try tonight. Thank you

 

[rm6p]

Ron,
I tried everything and still not centered. Valve #4 here I come. Thank you for the detailed information. From what I have learned from this endeavor ,the processes you described would have worked with a good valve. Thanks again

 

[mguesto]

i got my combo valve from here: http://www.getdiscbrakes.com/catalogsearch/result/?q=pv12
Right Stuff Brakes

$85.00 A brass Weatherhead that fits like original and mounts fine.

Matt

 

[rm6p]

Sounds good. I appreciate the link. I looked at them for a brake kit a couple years ago but got a deal on an original B-Body disc brake set up. Forgot all about them until your reply. I will give them a call tomorrow. Thank you.