70 Cuda Disc Brake Drag

I have replaced my entire brake system from front to back and now have stock power front disc with drums on the back. When I apply the brakes the fronts will not release. I opened the caliper bleeder and it releases. So it is not the calipers. I cracked the lines on both sides of the metering valve and the proportioning valve and each one relieves the pressure on the wheels. So that rules out the valves. I cracked it at the master and that relieved the pressure, so thinking that maybe it was the master I replaced it, however no change. I then loosened the master from the booster and that did not make a difference. I checked the booster push rod and it is adjusted all the way in. So in my mind either the booster rod is incorrect or there is something mechanical in the pedal system that is not pulling back. Any thoughts. Thanks.

Are you using a master for a front drum set up, or for a front disc set up? The master for drums have a valve in that port to keep the fluid in the line and wheel cylinders as the shoes wear, etc. The disc master doesn't have that valve. That residual pressure in the line will keep the disc pads applied.

Also if you changed from front drums to disc, you have to get a proportional/equalizer blocks for the disc brakes.

The proportioning and metering block are for disc/drum as well as the master.

Are you using a DRUM/DRUM master or DISC/DRUM master? if your using the original 4whl DRUM/DRUM master, #1 either install the correct DISC/DRUM master or remove the residual valve from the rearward port on the DRUM/DRUM master as that is most likely the cause of your residual front brake lock

What's the masters pn# or casting number?, or application you purchased it as

take the fitting/line off of the rear master cyl bowl half for the discs & stick a drill bit into the brass cone in the MC port & you will feel the RPV if it has one (its just a piece of neoprene and a spring) & if so pull the cone & toss it. confirm that you have ~.020" clearance between the round pushrod nub end & the bottom of the piston recess which I'm thinking you adressed when you seperated/pulled the MC forward. All that is left is a prop valve or line blockage. EDIT or a booster or linkage problem under the dash issue.

It is a disc/drum master cylinder. Raybestos MC36283.

I will check to see if the rear has a RPV and will swap out the prop valve tomorrow.

I am thinking that it is a booster/linkage problem under the dash. When the car is shut off and sits for awhile the pressure comes off of the calipers.

Appreciate the advice.

Holler what it ends up being.

Watch the Rammans video on youtube on testing brake boosters. Sounds like a popet valve inside.

I then loosened the master from the booster and that did not make a difference.

doubt it's the booster

And of course the front brake lines are attached to the rear port, and the rear brake lines are attached to the front port?

Thanks for everyone's comments, even though they were both new, it was either the proportioning or the metering valve that was gone. I replaced both and everything now works. New question: now that I have connected the brake lines to the valve I get a constant slow seeping of fluid. Not a lot but it drips over time. I have tightened them down but no luck stopping it. Lines are new and are the stainless steel type. They do not seem to be seating properly. Any suggestions? Thanks.

You can get some thread sealer that is specifically made for brake fluid. Coat the the threads and reinstall. I've used it at all connections and no leaks.

Loosen and retighten. SS lines seem to need that .

Stainless threads can gall easily, use the proper TUBE wrench so as to not EGG the flare nut, use some grease or teflon paste to lube the threads so that you can tighten properly and seat the flare nut fully, once you gall the threads or EGG the flare nut using a regular wrench it tough to properly seat the flare tightly

Thanks again I will try all of the above.