Jack up rear wheelS(both). Put in neutral w/emer. brake off. Have someone hold one rear wheel still while you try to spin the opposite one. If it spins ok, it's unlocked; if it is extremely difficult to turn, or will not turn, it is locked. Had an acquaintance lose his responsibility for ordering new cars when he ordered all GMC 4X4's w/o specifying locked differentials. Perhaps even a 2X w/posi-trac'n. differential will pull better than a 4X w/unlocked differentials?! s
It really depends on what you are doing. Limited slips don't create traction. If both rear wheels are loaded the same and are on surfaces with similar frictional characteristics, the limited slip isn't going to help much. Now if one rear wheel is unloaded or in a mud hole and the other is on firm ground, then a limited slip can save your ass. However, a limited slip can make it easy to loose the rear end on low friction surfaces and spin out the vehicle. Personally I'd never order a 4x4 without a limited slip rear axle. On the other hand, in 40 years of driving farm tractors with locking rear axles, I've never once had locking the rear axle get me out of a jam. The usual result of locking the rear axle is burying the tractor to the axle housing. But this is a situation where both wheel usually have the same traction available.
Ed
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