Anything under acceleration on a Detroit Locker in a tight turn should cause it to lock. They are set up so one wheel can coast faster than the driven wheel, but the driven wheel cannot spin faster than the coasting wheel, if that makes sense. They normally are quite harsh when they lock up, especially obvious in a 4.56 gear. Like some others mentioned, you should be able to coast around a turn with no problem or drive around the corner with neutral power. Under load, they should lock up. Another thing you may find is a bang when backing in a curve, then going to drive. If you catch the locker in the middle of locking up and reverse directions, it will ring your driveshaft. Harsh, but among the strongest locking systems out there.