c4 reverse problem
 

I have a 70's c4 that wont go in reverse. When the engine is running and I put it in reverse it wont go backwards and the engine sounds like it has a load on it. I had to replace the rearend last weekend after it locked up. After installing the rearend, I wasnt able to go backwards. It goes thru the forward gears fine. I assume it maybe the reverse band. Is there an easy way of telling? Pull the pan? I have never worked on transmissions before. The rearend ran out of greese and locked up. When I jack it up each wheel turns freely. Again the forward gears work fine. When I put it in "N" or "R" the engine sounds like it has a load on it.

Thanks for any information

Jeff.