Both the replies below are of course correct...but not quite as complete as could be. jack the car up (both rear wheels off teh ground) *and leave it in gear*. If it has ltd slip, it will be impossible, or very hard to turn either wheel. If no limited slip, car in gear, turn one wheel, and the other will turn the opposite direction.

Or, jack up both sides, *put in neutral*. If limited slip, both wheels will turn the same direction, and the driveshaft will turn too. If no limited slip, either only the one wheel will turn, as well as the driveshaft, or the driveshaft will remain stationary, and the other wheel will spin the opposite direction.

The burnout is by far the most fun... I recommend doing so on a dirt road though.

What year is your car anyhow? If its '69 or earlier, limited slips are rarer than hen's teeth. If you got one, take care of it. They ain't available no more.

If its a '70 or later (rear disc brakes), its got a standard Dana 30 rear with standard 27 spline axles shafts. You can get the posi units for them new from several manufacturers. Have a competent rear end specialist do the work. That is, a 4wd shop. They won't talk Volvo, but they'll know 'Dana 30' very well, as that rear end is common to Jeeps and several others.

-Matt
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-Matt '70 145s, '65 1800s, '66 122s wagon, others inc. '53 XK120 FHC