Hey guys I just put a used manual transmission (from an 83) in my 1982 Rx7 and reverse gear has been acting up. If I really give it any gas at all trying to go in reverse it throws it out of gear into neutral and grinds. I can go in reverse if I just use the clutch and no gas but then the car often stalls.
There is another problem too, where in first, second, and third gear I can hear a constant gear grinding noise. (Not nearly as unsettling as the reverse gear grinding noise), but it is still enough to make me thing there is something seriously wrong. I really don't know all that much about transmissions so if anyone could diagnose what is wrong that would be amazing.

 

I hate to be a debby downer, but it sounds like your trans is toast and is going to need a full rebuild.