How do you know if your transmission is going bad or your torque converter?

71 challenger 340 with 904 auto, when I floor it sounds like something is grinding. I babied it home after it did that and it seemed to shift ok.

Well I know in my case, reverse would take a lot of revving to get "kinda" going like it was slipping bad, which... it was. The reverse band was shot in my 727. A different time it was very slow to shift in between gears, and the clutches were shot. I think any of these sort of problems you should be able to tell by looking in the tranny pan/fluid for excess metallic flakes/debris or a burnt smell from the fluid. I didn't burn the fluid when reverse went out but it sucked having to roll backwards and hope I was on a hill , forward was still perfect but I put in new Alto Red clutches and Koleen steels anyway . Good luck!

Thanks for repling, my reverse was not solid at all and would require alittle rpm's to get going but still shifted in the forward gears fine. Now I think it time for a rebuild.

Thanks again!

So the first thing I would check is that all the troque converter bolts are tight. If one is backing out it will hit the back of the block under load when the plate flexes. Then I would pull the pan to see what is in the pan. If something is going away in the trans or converter you will have allot of gray sludge and or magnetic metal fragments. If the clutches are going away you wont get the grinding noise just slipping and burnt fluid. IF you have a big build up of the sludge and or metal it can clog the filter and reduce the pressure and cause slipping also.