I converted from drums to disc during resto but brakes are really bad, just wondering if i missed a step? maybe i need the booster? Using original style master cylender changed proportioning valve. I've, bled brakes many times...

Yes. The drum mc will work. A disc mc holds more fluid because as the pads wear the caliper fills. No big deal just check your level once in a while. Also when you squeeze the calipers open to put in new pads have a turkey baster ready to suck some extra fluid out of the mc so it doesnt overflow.

Try cleaning the floor real good or put down cardboard to find a possible small dripping leak. You said it's not a new mc right? So it couldnt need to be bench bled first?

I run manual discs on my car with no issues. What exactly is the problem? I used a M/C spec'd for a 1976 Plymouth Valiant with manual disc brakes. I think it was 1 11/32" bore.

need more info! what parts did you use? are these 1970s factory disc brakes? what master cylinder did you use?

yes, you can get manual disc brakes and have them work well.

check this forum for a LOT of brake information from sizing your master, to figuring out your line pressures:

https://board.moparts.org/ubbthreads/postlist.php?Cat=0&Board=Corners

You sure you have the right master? The piston changes between the years for power/manual operation. Maybe you have the 7/8" piston and you need the 1 1/8". I stole the disc's off of a 75 A-body along with the prop block and suspension. I loved my manual disc brakes. One less thing in the engine bay of a 70 Dart. Slant 6. Also make sure your brake lines don't have a bubble where the banjo is, might have fluid escaping or sucking air in with every pump. I use the stainless braid on brake lines.

The best brakes I ever had were manual discs that were factory on 67 Dart GTS's.

I did a Master Power conversion and had horrible brakes. Bled them 4 times and still no pedal. Called them and found that the calipers were not mounted high enough to bleed all the air. Rotated them up another bolt location and now they are solid as a rock. Fantastic system. Even without a booster they are easy to use.

Awsome advice guys! At this point i cant get at it, but will have it up on a hoist this week, im sure he put in a factory replacement(or aftermarket but looks like orig.)The master was bench bled, all new lines, gravity bled (whatever that means) and bled again. but the brakes really suck (seem to be getting worse and going to floor now) so maybe there is a leak or air still in system.
I will keep you posted when i get to it this week (i hope)

My 74 dart had factory manual disc brakes. That was the best braking mopar I ever owned. More than enough stopping power and provided really nice road feel when on the brakes.

You need to post some info on the car and parts used,.....the drum/drum master has to go though, use a correct disc/drum master, bore size could be determined if we knew the type/size of calipers used, rear drum specs, etc, etc