1. Make sure the springs are engaged properly on the post and putting force on the brushes
2. Pull the brush shunt lightly with the spring engaged and see if it slides in and out smoothly, then let it lay back onto the comm
Try the motor now, if it doesnt work continue
3. Take off the spings and slide the brushes out of the hoods, make sure they are not cracked
4. Make sure the brushes slide smoothly in and out of the brushhood if not clean or re-side the brush hoods
Re-install brushes and springs, try the motor, if it doesnt work, take it to a hobby shop and have the tech guy there look at it...