[Ron61]

I am not familiar with the True-trac unit, but my 69 Cobra came with the SVO posi unit in it and if I jack up just the right side I can't turn it as the left wheel holds. Blykins gave the simplest and easiest quick check. Just get both back wheels off the ground and turn the right one as that is the drive wheel on all older cars and if the left wheel turns backwards while the right wheel is turning forwards it is an open rear end.

Ron