Bob, it's basically anything which permits the output shaft to move in the opposite direction to the gear thus increasing its travel relative to the hub - in '97 I concluded it was a combo of worn synchro cones (not replaceable at reasonable cost so far as I'm aware, only by picking from another box) and excessive slop in the end bearings (which are easily replaced and shimmed as necessary).
Worn/ stuck detent balls and springs in the hub are certainly a factor; I'm not sure though whether it's possible to expose the balls if axial free play is under proper control, I suspect not. I do recall I selected 1st gear fairly briskly which probably didn't help. One thing I (or rather the Bosnian mechanic who helped me) did at the time was to put a spot of weld on the selector gate, thus restricting the travel of the selector to the necessary amount.
I wouldn't want anyone reading this to draw the impression that 4 speed boxes are unreliable - I've done nearly all my A7 motoring on them. They are however perhaps less tolerant of neglect than the crash boxes - maintain them once every few decades and they're fine. If you are methodical they are not unduly difficult to work on.
Worn/ stuck detent balls and springs in the hub are certainly a factor; I'm not sure though whether it's possible to expose the balls if axial free play is under proper control, I suspect not. I do recall I selected 1st gear fairly briskly which probably didn't help. One thing I (or rather the Bosnian mechanic who helped me) did at the time was to put a spot of weld on the selector gate, thus restricting the travel of the selector to the necessary amount.
I wouldn't want anyone reading this to draw the impression that 4 speed boxes are unreliable - I've done nearly all my A7 motoring on them. They are however perhaps less tolerant of neglect than the crash boxes - maintain them once every few decades and they're fine. If you are methodical they are not unduly difficult to work on.