what are the strongest gear's I can buy?

ZEATER said
Just make sure you order the street gears. Some race gears are not made to handle the heat generated on sustained street use and can become brittle. It will be interesting to see just what broke inside the carrier. It may not have been the gears.

They only make street gears for the 8 3/4. I've never seen a 8 3/4 pro gear made yet :( Hopefully soon.