I just did a complete rear swap and I have little brakes from the rear. I went from a 92 firebird drum to an 89 formula 350 disc. I know the problem is one of 2 things. The calipers' bleeders are broke so I can't bleed through the calipers so I loosened the line to do it. The other thing is I may have to change the master cylinder and p/valve. I read on many occations where people didn't have to do that, so I was kind of hoping I didn't have to. Anyway someone please tell me what you think the problem is.
Thanks Wes

 

get new calipers and bleed them the right way. through the line you still have all the air in the caliper.

 

Are the calipers on the new rear aluminum? If so, then your 92, drum master cylinder is correct for the disc rear. All 89-92 master cylinders are the same. The rears with the cast iron calipers (88-older) require a different master and prop. valve. With the aluminum calipers, you can get away with using the drum prop. valve, but it does work better with the disc valve. Even if you have all the air out of the lines, the disc rears are notorious for not getting enough pressure to the rear calipers. There's two ways to alleviate this problem. The first way is to get the 1LE prop. valve. It gives the most pressure to the rear calipers out of the factory valves. You'll need the 2nd design, 1LE valve since the thread pitch changed in 1990. Or, if you know how to cut and reflare the lines, you can ditch the factory valve and install a Wilwood, adjustable valve. This works even better than the 1LE valve, and there's a great tech article here on the site for doing it. I've still got to get around to changing the valve on my 89. My brakes are perfectly bled, and when I had the rear up on jackstands and put the car in drive, I pretty much had to stand on the brake pedal to get the back wheels to stop spinning. There's always posts about this on the brake board since it's such a common problem.

 

I wanted to thank you both for helping. I got some new calipers the day after I made this thread and forgot about it. They did solve the problem. I had to do something because this car is my daily driver. Anyway thanks again for replying.
Wes