I pulled the cover off of my rear diff to change the lube and it looks like a regular single track rear diff.

I could not see and kind of clutch pack or locking mechanism in the carrier. The 4 spider gears and shaft were all I could see in the carrier.

Can someone explain how the Ford LS works?

 

Check the tag on the diff. There should be a 3L55 in it denoting 3.55 gears and the L for limited slip. You can not see the clutches in the 9.75 they are hidden by the carrier.

Jack up the rear and turn one wheel. The opposide side will turn the same way if LS and the opposite way if open.

Regards

Jean Marc Chartier