Ok, I will try and be as succinct as possible without ripping Atomic too hard since they have a history of making great products. Here is all of the testing and investigation I did tonight and ultimately, it was a waste and had to go back to Kyosho ball diff. I really want to use this diff but I need to do some engineering recon still and I will keep y'all posted.
PROBLEMS:
1) No instructions and this is not a plug n' play product.
2) Spur gear is not round!! - no matter how you set mesh, the molding on the spur is not accurate enough to be considered round in this scale.
3) Gear tooth pitch is not right - unless they are providing an Atomic pinion gear set, these never mesh right.
4) WARNING: There are 6 screws. They are of 2 different lengths! The long ones are for using the plastic hubs and the short are for the aluminum.
5) WARNING: Aluminum left hub needs modification! No matter which screws you use, there was a total bind when the screws were tightened even to the lightest amount where they would back off.
6) Shim may be needed. When all is said and done, there is not enough gap between spur and motor mount... it rubs!
7) The tolerance of knurled adjuster is VERY small inside motor mount and the diff backed out and undid itself! Not sure if it was from this, the rubbing spur, or the tight mesh... but the diff was unusable and felt like constant drag brake at best.
FIXES:
2&3) I have a brand new Kyosho ball diff I am going to take apart to see if ID is the same and if the balls fit. If so, this should solve majority of the problems.
5) The problem was the aluminum Kyosho hub was too long on inner step and diff may have been designed to only work with plastic hubs. There was tons of material on left hub so I got some 600 grit sandpaper on the granite countertop and took some material off the hub where it meets the axle/e-clip/bearing. Once I did this the short screws torqued up nicely and no more binding.
7) I may end up with a round roll of emory cloth to take some material out of the motor mount where the diff slides through. As it stands there is like 0.1mm of space and that equates to 0.05mm per side of the knurled adjuster. If you know about plastic molding... no way this can be perfect in these tolerances. This will be the last thing I mess with though.
NOTE: it would be one thing if I was a rookie writing this up, but anybody who knows me in the Mini-Z community (or r/c community in general) knows I am fast and have a good mechanical clue
This product needs to get a rev2 before re-releasing and I kind of expect Atomic to make good on the product without sticking me for more money.