At some time or another it has been stressed too much, and one or more of the balls have fallen out of it. If you owned the car when this happened, and have recovered ALL of the balls, it can be rebuilt. If you dont have ALL of the balls, try picking one up at that famous auction site. They are listed on there from time to time. One other possible fault is that your column may not have the cable stops installed and it has extended too far. See TSB's