What may be the possible causes of my automatic transmission ceasing to operate on my 1985 300TD.

It happened al of a sudden, reversing for a little stretch then putting it in park there was some funny noises idling, then it stopped. Now nothing shifts. Engine revs up in all gears but nothing happens.

I replaced the B2 piston about two years ago, so I doubt its that but could it be?

Any other Ideas and what the remedies would be?