As to rear brake use, When getting off the roadway onto a soft shoulder, The front brake must be backed off and use of the rear brake increased.
If not the front wheel will wash out.
I use the rear brake instead of the engine braking. In my mind, it helps the rear tire last longer.
For the tight, loose, tight, loose in the brake, Could it be that not only do the shoes need to arched, but also that the drum has gone out of round?
After re-arching the shoes, Could you place the sandpaper on the brake linings, then rotate the wheel while using light pressure on the brake?
This would leave scuff marks on the drum to show any high spots.
