82 Chevrolet 3/4 ton truck with a TH-400 trans. It suddenly began making a grinding/whirring noise in only first and reverse. Second and third are absolutely quiet. What might have happened? Sprag, broken or ejected snap ring, broken snap ring land in case, planetary, or what? I'm not a trans guy, but have rebuilt several; mostly Glides. I do have a spare TH-400 meant for a Bracket Car I'm putting together (slowly). Course I'd rather not have to go that route. I tried looking in the "search function", but I've NEVER gotten anywhere with that. Also, there's nothing in my Chilton's about this issue in the in/out-ABC/abc trans trouble shooting section. HELP! I am Butch/56sedandelivery.