Rear End?

I was driving ( 75 Datsun 280z )going about 30 in 3rd gear and started to slow down to turn onto another road and then i heard a Bam!. my wheels didnt lock up or anything i just stopped the car and got out. I looked around because i thought i had hit something. i looked under the car and there was nothing hanging or no liquid on the ground. so i got back in my car started it back up put it in first gear and started to move i moved about a foot and then that was it. My car wouldnt go anywhere. The clutch still has the same pressure as i did before the Bam so i dont think thats what the problem is. its still goes into gear like i did before. I got my car up in the air and strted it up and put it in gear and my wheel spins just like its supposed to. So i took a board and stopped my left rear wheel and my right side wheel didnt start spinning. It seemd like it wanted to but it wouldnt. I talked otg my grandpa about it and he thought it might be a gear or a bearing in the rear end. I was wondering if anyone knew what the problem could be. It seems the tires dont move when there is any traction. If anyone could help that'd be graet. Thanks alot
Jeremy Hardin
Naples, Fl