Originally Posted by
SC10 Rookie
Slap the guy at your LHS for misinforming you and buy a ball diff. Try one for yourself. They outperform and outlast the gear diff hands down. And if you are racing you need one.
Also, tell that guy at the LHS after you pimp slap him that the Ball diff is installed in the same place as the Gear diff, WHICH IS SEALED IN A DIFF CASE... So, no dirt/clay/dog poo whatever has EVER gotten into my ball diff.
As for the gear diff handling more power, I am not 100% sure about that, but I had 2 fail during races running an 8.5. No problems with a ball diff though. Get that guy a book, and have him read it.
Or just copy and paste that ^^^ and send it to the guy at the hobby shop, it's right on.
And if you can't get the direct drop in ball diff you can get the T4 ball diff, get a T4 diff case $7.00 and two $7.00 bearings for the out drives and everything else drops in.
I ran both the gear and ball diffs on a MM5700 & 40C 2S lipo and had no issue with either failing, but with the bigger motor I did notice the ball diff was better for hard traction. My first set-up with the ball diff I used the wrong grease and had a hard time getting it to not slip. I re-greased with the AE ball diff grease and it works great
(yea don't use the black grease on the diff rings 
).