My son purchased an 88 series III, 1982 which was refurbished 7 years ago. It looks like they used any year part they had. The car has been sitting awhile. The brake paddle was going almost to the floor. We found both rear cylinders leaking. Both changed with new 1-inch cylinders and new shoes, adjusted. all 4 drums are 10 inches. After bleeding with Castrol Dot 4, there was no change in the paddle. Through the master cylinder might be bad. Changed it with one that came with the car, it looked new, an old CV type. No change with brake paddle travel, after bleeding. Looked at the front brakes, no leaking but one cylinder was frozen, both front brakes are 10 inches, with 1 - ¼ inch cylinders. We changed he cylinders to the 1-inch, new shoes, adjusted, bleed and still no change to the paddle travel or stopping. All brake lines are good, including flex hoses. What is our problem and what do we do to fix it??

 

It’s been years, but I did have a similar issue. I had 2 issues, my drums were worn beyond limits, and the brake adjuster mechanisms were sloppy. This may not be your issue, but if so, the parts are readily available and not expensive.