The Detroit locker rear ends were only made for either 9 inch or the newer 8.8 rear ends, like those used in a Ranger or Bronco II. They are still being made to this day as an Eaton product. If the rear end that you have has a cover plate on the back which is held on with a bunch of bolts, that's an 8.8 rear end. If the rear end has center section which loads from the front and is held on with a bunch of nuts, and you can't get a socket wrench on the bottom two nuts, that's a 9 inch rear end.An 8 inch rear end has the nuts on the front, also, but, you can get a socket on all of them. There was also a limited slip version of the 8 inch, but, it was not a Detroit locker. If the rear end is a limited slip or locking differential, you need to add a bottle of the friction modifier that is available from the parts department of any Ford dealership. It's not at all expensive. Hope that helps.