Just so we understand which rear end we are talking about, mine is an open rear. If I jack up the rear of Ol' Yeller so that both tires are off the ground, and I have my manual tranny in neutral, if I spin the driver's side wheel, the passenger side wheel will not move. If I spin the passenger side wheel, the driver's side wheel will not move.

 

that's how i know it as well from open rears.
both wheels off ground. Spin one wheel and the other will turn the exact opposite way when the driveshaft doesn't move.

if you check on
http://auto.howstuffworks.com/differential2.htm
you see in the 2nd picture how this thing works. it's an animation.


Now imagine what the other wheel will do when a wheel turns and the driveshaft does not move. It will cause the other wheel to turn backwards
the ring gear doesn't move, but the 2 red gears cause it to turn the other way round

I was fascinated by that back as a mechanic. took me ages to figure how that's possible but still both would turn the same way when you drive ;-)
but only when the driveshaft doesn't move. So if you have the car in neutral the driveshaft might move instead of the 2nd wheel which will cause the 2nd wheel to stand still

Kalli

 

Probly close to a grand, sad to say. Assuming you have someone else do the whole thing anyway.