Are you talking about the shaft the governor gear rides on or the shaft that the arm fits on? If it's the gear shaft, first measure the height to the groove first and grab the shaft with a pair of vice-grips or similar and pull it out and put a dab of J-B Weld on the new one and install it so that the groove is at the same height as the old one. And use a new governor gear and button if the old one has been removed from the shaft as the plastic tabs that hold the gear in the groove will be distorted and could cause the gear to fail within a short time.