8 3/4 rear end worn out or not?

Yea, it could be a worn out SG unit, and if it's originally from a 72 Charger it would be the cone style Auburn unit. When the side of the cone wears out from contact with the side of the housing, the cone bottoms out...no contact with the side, no SG!!!

This can be repaired by machining the bottom of the cone and adding the amount of removed material in shims on the top of the cone to maintain the required thickness, but if the housing is scored you will be looking for a replacement unit. It is imperative that you investigate this immedietly to prevent further damage to the housing if you plan to continue using this unit.

Removing the center section of the 8 3/4" is really easy, and I would think about doing so soon to inspect the SG and to verify just what it is you have here!! Take a pic and post it here for verification if you're unsure of what you have when you get it opened up. Wern't you unsure of it's ratio also?? You can also check the ring gear for verification of the ratio while it's open also!! And, it being a 489, now would be a good time to add the hard spacer in place of the crush sleeve if you're planning on rebuilding this unit!!

Good luck and keep us posted!! Geof