I had 3.73 posi installed last year. TOday I had a flat tire, and put on the spare donut tire. I was driving home, I was not driving fast, I had to slow down to turn off to a side streeet. As I was turning my tires spun on a bit of ice, and there was a clunk, and it sounded like I was now travelling on the donut rim. I got out and check the donut, it was fine, but as I continued to drive it was like I was dragging the tire (like the wheel was not turning).

When I hit that ice, because of the different size tires and the posi, would that cause it to screw up my diff???

Not "screw it up" as such; but if you have the Eaton Grenade-Lock (Eaton calls it Gov-Lock, the rest of us call it the other thing)posi in there, it may have locked itself up, and now can't unlock because the 2 different size tires keep force on it all the time. It will probably go back to normal when you put the right size tire back on it.

This ice isn't a problem. Driving very far at all with different size tires on the rear is bad on the posi(limited slip). It makes it slip constantly(wearing itself out/heating it up). Or, if the posi is 'good' enough, the small donut tire may not have enough traction to make the posi slip, and the donut tire is being dragged to some extent. The smaller donut tire needs to spin faster than the normal tire, or it will drag.

So what you are saying there is a good chance that when I get the normal tire on there it will be okay??

Basically, yes.

Ouch! Never do that!!! Good way to burn up the clutches!!

Next time, take an extra 15 minutes and put the donut spare on the front, and put the front tire on the rear. Or use fix-a-flat...

Well, I never really new better, till it happened then I kind of new what I did.

Speaking of Posi, I was wondering... does the differential open when there is no power being driven to it... ie going around a cornor with foot off throttle. I thought that they were, but I want to be careful. My new IROC has the BorgWarner 3.27 rear end, which I beleive is posi, and I've got to drive it home from Boston to Upstate NY tomorrow, and the weather isn't looking pretty. I just don't want to get away from me becasue it was dragging a tire off the power going around on and off ramps on interstates. I drove a friends car once with welded spider gears (Don't ask, not my idea) and it was insanity even on dry days. Point being, I don't want to fool around with those problems, I'm just wondering if the posi unlocks off the power? Thanks.

the posi is always locked to some extent. It slips enough to allow the tires to turn independently in most conditions but doesnt allow them to have large realative speeds with respect to one another. On ice/snow, depending on how tight the posi is and how slick the road is, it may not allow the wheels to turn with respect to one another.