rgnprof,
I learned something with the rear drum brakes on a dual rear wheel axle (originally a SRW) on our old 1983 Toyota motor home that I believe will be applicable to your problem. Like you, the rear drum brakes were not working. In my case, this was when the original SRW axle was replaced with a true DRW axle. What I did, completely changed the response of the braking system with the 4 rear tires contributing immensely in stopping the motor home. When I was done, I could actually feel the rear of the motor home sinking from the rear axle holding the rig back with great rear drum brake performance. This is what I did which was all about how I adjusted the rear brake shoes.
- lift the rear of the motor home and place the rear axle on blocks
- leave everything assembled, tires and all
- place the transmission in neutral making sure the rear tires spin freely
- focus on one side
- access the adjusters and adjust until a drag (so far it's a text book process)
- have an adult press the brake pedal as hard as they can
- if the wheel spins, adjust again
- do this several times (I counted 18 times on one wheel in my case)
- repeat on the other side
- when done, go back to the first side, then the other side
- when you think you are done, turn on the engine and pump the pedal several times again using the power brake booster
- turn off engine and check for a decent drag on each side
- I had to adjust the brakes tighter multiple times again
The rear brake adjusting process went on and on (and on)....did I say on and on? I thought I would never get the rear brakes to drag significantly to require a little muscle to turn the tires.
I drove the motor home around town and checked for over-heating, but there was no concern. I also checked for rolling resistance which was of no concern. The next drive was a longer test to my job which also was uneventful. So I considered the job done and the brakes performed perfectly for the many years we owned the motor home thereafter.
I think what made the difference was having the rear axle raised up so I could switch between sides as often as needed and checked each brake, and adjust tighter and tighter again. I was very surprised how many times I had to re-adjust tighter after I thought I was done. It took so many tries to get each brake system seated properly into their respective drum, but the results were amazing.
There is no way a mechanic would spend the right amount of time adjusting the brake shoes on that old rig we owned. As torturous as it was to do on my back with the tires on, it was surely worth it all.