83' Silverado with 6.2 diesel transmission clanked and then no power

I have a 1983 c10 with the 6.2 Diesel engine. Got in it one day and started out the drive and herd a clank/pop and lost all power and coasted to a stop. Motor running fine, but transmission just won't go. Not making any grinding, whining, or popping noises. Any ideas of what may be wrong?