Thrust Washers
 

I was interested in tightening the play in the differential of a 66 Coronet and was wondering if anyone knew where to get the side gear thrust washers in various sizes to do this? Or do they even exist? Thanks.

rear end shims
 

the 8 3/4 doen not use side thrust washers for the ring gear. It has threaded adjusters. Some shims may be used for the pinion gear to set its depth. Randy's ring and pinion, www.ringpinion.com has everything you could need. It may be possible that your pinion nut has loosened. Usually the gears do not go out of adjustment, Gears may be toast.

I was actually hoping to tighten up the play between the side and spider gears.