Jerky motion equals the motor is not quite indexed.Pull The arms off. Run the wiper and let it "Park". Look under the dash and see what position the link arms are in. Some adjusting(mine has a nut to mount the motor to the bracket and a screw to clamp it) a little repositioning should stop the clank and stutter. Then put the arms on and index them just above the rubber seal for the windshield. Some arms have an adjustable end that allows for adjusting the position or the rubber wiper blade. and others do not. If you have the adjustable type, the shorten the arm until the blade is about 1/2 inch from the center bar. Should work from there. If the motor won't index until you have no clanking, the Arm on the shaft may need to be repositioned and then start over. The start and stop point is determined by the "park" cam so that is where I start. I know it sounds a bit clumsy, but when you see it all move under there it will make sense.
