Finding an axle you think you’ve always wanted is awesome. First step is to unlock the hubs (If your axle has them) and try to turn the axle’s pinion via the yoke. It should turn freely. If the pinion doesn’t turn and the axle doesn’t have locking hubs, or the locking hubs are not working, all hope is not lost. A rusty brake or hub may be preventing the axle from turning.