I have tightened the diffs down so that the main gear does not spin when holding both ends. I am able to twist the diff, which seems logical to me. (I have not had a kit with a ball diff) I only built a kit with metal gears. Should I torque the screw down even tighter? As of right now, the car moves better than before, but the diffs still spin when giving it power. I am only testing with a 21 turn motor, which shouldn't be too much power. My brushless system hasn't arrived yet. Any suggestions would be greatly appreciated. Just so you know this is my first build in like 10 years.