1980 Cj Brakes Wont Bleed

Hey guys.
I'm trying to help get my father-in-law's CJ Resurrected.

It's a 1980 CJ, and for the life of me I cannot get the back brakes to bleed.
ordered a new master cylinder. new master cylinder, bench bled to perfection. still nothing.

Nothing works! I'm squirting juice out and dont see air bubbles coming out when we bleed it, but it's not holding pressure in the back. the calipers do squeeze and I have to manually clamp them open them to put the pads in to install over the rotor.
when we go thru the bleeding sequence again, same results.

we do back pass/drive, then front pass/driver side.

if i pump the brakes afterwards i can get it to have pressure at the middle of the stroke, and will stay, with no pedal fade forever. i take my foot off for a second or 3, start the pedal depress and again it goes to the floor.

I ordered two new rear calipers, but is there anything else I can try in the meantime?
I did fiddle with the proportioning valve a little and it seemed to work for a second or two.

maybe it's a bad master cylinder?

disclaimer: it's been sitting and rusting away in a damp garage for the past 10 years

 

Could have pulled a piece of junk into the bypass in the master out of one of the hard lines, my brother had a similar issue with his jeep.

 

How did you prepare the rear brakes? I suspect that, if the brake linings are far enough off the drums, when you pump you can build up enough volume to move the shoes against the drums. Then if you release, the springs pull the shoes back. You don't have enough volume in a single stroke for the shoes to reach the drums.

Calipers on the front, cylinders on the rear. No calipers on the rear.

 

This I don't like. Need to be 2 , to help. Need brake fluid. need pump.for fluids. need to stay under the car.
Need to note each move. to have wheels and drums away if useful.bori g take your time !

 

4 wheel disk. 80 monte Carlo calipers

 

Put new calipers on the back to rule the old rusty ones out. Looked at the front passenger side, and the bleeder valve was at a low spot. So the air was trapped at the top and couldn't escape!

We got the brakes working now. New tires should arrive some day this week, and then it should be ready for the Northwoods.

 

New tires on, and maiden voyage after 10 and a half years of sitting.

 

Looks awesome, and I think you’ll really like those 4 wheel discs! I’d find some gravel and do some brake checks to make sure your brake proportions are good, or the rear not locking before the front.