First of all, even when they're working they're a piece of ****.
The official procedure does not call for only reverse stops, but the FSM does point out that the adjusters will only operate if you bring the vehicle to a full stop, not a rolling stop. After brake work, you're supposed to do 8 to 10 cycles of back and forth full stops.
Check that the crescent-shaped cable guide that presses into the trailing shoe is properly seated in its hole. It just sets in there, and the spring sort of holds it in place, but if it isn't seated right the spring will just as happily hold it out of place, causing the cable to have too much slack. When it's set up properly, the pawl should be resting right on the star wheel of the adjuster.
Make sure the adjusters are for the correct side, and installed right way around so they don't unadjust instead of adjusting. If the parts are old check that the edge of the pawl is not worn round, and that the teeth of the adjuster are not worn, blunted or clogged with junk.
Finally, since they may never work all that well, and often don't adjust consistently on both sides at the same time, I'd suggest that you periodically adjust them by hand anyway if you really want them to work right.