Refer to the diagram. Your issue most likely is in the mechanical path starting at the adjusting wedge, adjusting shafts, brake pin, pins holes and drum.
The operating cam is not in the line of action causing the problem.
I realize that you have replaced rear brake parts with new ones, but which ones did you replace? Consider these causal factors:
- Adjusting wedge conical surface is worn. This necessitates the wedge to go in further;
- Adjusting shafts are worn. The wedge end of the shafts have a blunt point that rides on the adjusting wedge. The blunt point wears requiring the adjusting wedge to go in further;
- The pins connecting the shafts with the shoes wear, and so do the pin holes in the shaft and brake shoes. The adjusting wedge would go-in further to take up this wear;
- Brake lining thickness affects the amount of travel of the adjusting wedge. There are woven linings and molded linings. Originally, the woven lining material was 0.172" to 0.182" thick, and the molded linings were 0.162" to 0.172" thick. Wear makes them thinner, especially on the molded linings which wear faster;
- The wall thickness of the brake drum also has an affect on the travel of the adjusting wedge. Original 11" diameter drums had a wall thickness of 0.140". Cutting the inside diameter reduces the wall thickness and causes the adjusting wedge to go in further;
- A rare occurrence, but check it anyhow! Is the adjusting wedge housing loose?
- Another possibility is wear of the wheel bearing / bearing journals which allow the brake drum center to rise. The axle housing journal wears on its bottom from 5 to 7 o'clock. The same wear occurs in the brake drum journal;
- A loose backing plate also allows the brake drum center to run-out.