RCU Forums - Vocano S30 diff. trouble

Hello, I'm having this issue with my Volcano S30 rear diff. It's fairly new but I noticed a skipping sound in it so I took it apart and realized it wasn't making good contact between the crown and spur gear so I shimmed them closer together with washers behind them. They make great contact and no skipping or binding when its in my hand but, as soon as I put it together and run it I don't get rear wheel spin on acceleration. I checked all the grub crews on the drive cups. I don't know what to do now. Does someone make better quality gears for this?