I bought a 1983 Z28 Camaro with a 4 speed Automatic transmission a few days ago and was forced to use it with low transmission fluid for a few days. I added some fluid yesterday before I left for work and began to run fine. Coming back from work is when the problems started, I stopped for a while and turned the engine off, and when I returned, turned it back on and shifted into reverse, the car made a grinding sound and wouldn't move. When I shifted it into neutral to try and push it, it wouldn't budge, but it did move when it was in reverse. Worked fine in drive, though it was very jerky getting into those gears, as if it was out of fluid. I checked it, and it was full.

I'm really at a loss as to what it could be.