RCU Forums - diff problems

Wondering if anyone can help?? Common diff problem I have been seeing in several forums but have yet to actually find the answer. Took apart both my front and rear diffs to install my cvds. Took apart both my diffs and refilled since both were empty. Made sure to tighten the three diff screws evenly. There is no damage to my ring or pinion gear at all. NO sand or dirt was located inside my bulkheads. When I put it back together, the ring and pinion gear grind in certain areas as it rotates, this is before I even screwed everything back together because in previous post its essential that you dont over tighten because it will cause grinding. For others who have experienced this similiar problem did you shim the diff?? Now what is the best way to shim the diff for this particular problem? Every thread said to shim the diff but doesnt exactly detail how like put a shim on the ring gear and or pinion gear. It doesnt appear that there is any side to side play when the diff is in the bulkheads. That grinding is really getting on my nerves if anyone can please help...