Get two long, flat screw drivers. Put one all the way in until you touch the bottom splines. It should turn freely forward and backwards. Now use that same screw driver and keep the lower spline from turning. Use the second screw driver and contact the splines above the lower one. The upper spline should only turn in one direction with no tight spots. if it turns both directions with the bottom spline locked, it's bad. If there is any rough feel to either splines while turning I wouldn't use it.