if you disconnect the linkage from the servo do the wheels move side to side freely with no binding? If so then most likely a bad servo. When you have the linkage disconnected turn the kit on and turn the steering wheel on the TX left and right and see if the servo is turning smoothly in booth directions. If it doesn't then you know for sure however if it does that doesn't neccessarily mean the servo is good. If it were stripped it could spin fine with no load but you put a load on it and it could have that problem.