I'm having a problem with ice around here in parking spots. I've had a couple instances where one tire would be on ice, and the other on dry pavement, but when I try to get out, the one on ice just spins and the other sits there. Isn't this part of the reason for a posi rear? When I do burnouts, I can leave two strips, and I just tried earlier to make the the posi wasn't smoked. Also, the car only has 69k miles on it, so I can't see the posi being bad. The only reason I can think of for it doing this on ice, is that there's so little resistance, that the posi is slipping, and letting one wheel spin more then the other, such as when turning. If this is the case though, how come the other wheel does absolutely nothing? Shouldn't it push at least a little bit? Please help.

 

Part of the reason is the nature of a limited slip differential. When one wheel is on ice and one on firm ground it relies on preload spring pressure to apply the clutches.
When both tires are on solid ground and you give it throttle there is an upset force in the spider gears, that means they try to un-mesh from each other, this force pushes the side gears into the clutch packs and engages them tight.
I would assume you have a factory posi, most factory units are set with little preload to make it safer to drive on slippery roads.