That would be the way to tell if the diff was locked. Most LSD's don't kick in until a certain amount of torque is reached. A LSD is still an open diff until one wheel starts to spin much faster than the other. Clutch plates then start to transfer some of the torque to the other wheel. LSD is better than an open diff, but not as good as a locked diff.

Best bet, save up the money until you can get lockers.