I opened it and found the worm gear was worn and allowing it two jump and then jam the drive screw so I replaced it as well as new thrust bearing and of course new washers now it works however the next time I will replace all the gears and bushings and the gear case because it is much more noisy than before and other parts may be worn that are hurting alignment also it good to note that the screws appear to be Philips also accept a 2 square Robertson driver and this works better