HBI Maverick quantum r. Flux grinding loud

[Jasonkellam]

I recently bought a Maverick quantum r Flux rally truck 4S. I changed the spur gear in it and now I'm getting a horrible loud grinding noise from the spur gear and my rear. My rear doesn't want to move only my front will go

[Bajadre]

whats the mesh like between the pinion and spur buddy? could be too tight could use the paper method slide a piece between when setting the mesh up etc double check its not the rear diffbox by removing the pinion completey and rolling freely along the floor if no noise it will be the pinion and spur mesh if still grinding chances are somethings broke in the rear and needs opening up  and a part replacing 👍