Originally Posted by Waflet

Hideeho
The gear dif uses a different case & out drive bearings the the ball dif. If you started with an RTR it came with a gear dif & would need a new case & bearings to run the ball dif. If you started with a FT or worlds it came with a ball dif & would need a new case & bearings to run the gear dif.

Go to rc10.com & pull the manual for the b4.1 RTR & the b4.1 ft or worlds & compare part #'s for the case & out drive bearings.