I had the same problem , it was my brushes in the motor they had worn down. Hope over to a Radio Controlled car hobby shop and pick up some brushes from an RC motor ($6). There will b 2 brushes on a wire make sure you get the ones that have the wire coming out the back and not the sides. Now the brushes will be a bit big but thats no problem as you can sand it down to fit inside the housing. Remove the screw that hold the motor in place and unclasp the 2 plastic clips that hold the motor in place. Angle the motor at an angle and unhook the springs that push the brushes to the armature. pull out the brushes, unscrew the 2 screws on the bottom and remove the magnetic housing the armature (large motor looking part inside the housing) the top is where the brushes make contact with the armature sand it down so it is clean and shiny again, blow out the housing to get rid of any dirt inside. Now clip the wires and measure the wires so it will fit snug in the housing and sand down the brushes so they fit smoothly...