Two of the wheels wobble and have almost no drive... (Ruckus 1:18)

[JEBmi]

ECX Ruckus 4WD (1:18)
Two of the wheels wobble and have almost no drive to them the other two work fine. I made them tighter but it did nothing. What do I do?

 

[kontu]

Take the wheels off check the hex drive on the shaft and inside the wheel for stripping