junk the factory differential, there poor quality, trade up to hpi racing hot bodies part# hbc8178 there hardened and helical cut, they handle the power of my modified nova rossi motor with no problems, prior to finding these I tried different weight oils, shiming, teflon grease, and still broke diffs in two laps after installing the nova rossi motor, keep the 7000 wt oil in the center diff!! min!! I run 10000 wt and no more gear problems