I've never taken my diffs appart on my Axis before so I decided to check them out inside. When you turn the differential joints you can hear rough gearing. I opened it up and theres practically no grease in there. What grease do I get and do I pack it in when I refill it and rebuild? Thanks yall.

I must say I have no experience with the diffs on the Axis, and I don't know if they are properly sealed, but if they are, then you should fill them with silicone of appropriate weights to limit slightly (or significantly) the diff movement, and dramatically improve handling. Most RTRs differentials come with simple grease, which whilst providing lubrication, does nothing to improve the handling of the car. A suggested starting point for most people with regard to filling the diffs is to use 5000wt oil in the front diff, 7000 in the center, and 1000 or 2000 in the rear. But depending on the characteristics of your track and driving style, you may find that something totally different works for you. There are people on this board advocating the use of 5000 throughout.

If you decide to just use grease, then don't 'fill' it, but put a good amount in there.

The same should apply if you use silicone oil - you don't fill the diffs completely.