Rigid rods on a pull-pull system is almost a sure fire way to get into trouble. Unless you are absolutely sure that you have zero Ackerman set up, the controls will almost certainly start to try to bind up as soon as you are off center position. Always use flexible pull lines and try to have just a little positive Ackerman set in. This allows the line not being pulled to slack off a bit as the other line pulls the surface off center and puts no undue strain on the servo.