While sewing is something has been done for centuries, sewing machines have a more modern history. The first practical sewing machine did not appear until the late 1800s, and when it did, it began, as the Museum of American History stated, to be a "real competition to hand-sewing." The sewing machine relies on gears for its operation. When the hook gears do not work properly, the machine will not function as it should. Fortunately, you can replace the gears yourself and help your sewing machine work well again.
Lift up the presser foot on the machine. Loosen the thumb screw that secures the presser foot arm, and put it aside.
Remove the needle plate and the bobbin plate and lay them aside as well. Remove the bobbin and the bobbin case. Lay the sewing machine on its side so that the bottom is facing you.
Remove the bottom covers. Make sure you put them safely with their corresponding screws to make it easier to put everything back together. Locate the shaft that runs the length of the machine.
Turn the machine so that you can see the back of the machine. Remove the screw that holds the back cover in place and set it and the screw aside. Remove the screw that holds the power supply in place. Move the power supply down a little so that you can slide the shaft of the machine toward the back.
Turn the hand wheel and insert an Allen wrench inside the machine to loosen another screw, thus freeing the shaft.
Loosen the screws for the gears. One screw will be located near the middle bottom of the machine and the other near the bobbin case. Slide the shaft toward the back, freeing the gear you need to replace. You may have to remove a clip at the back end of the shaft. Set that carefully aside. If you cannot remove the gears easily, you may have to loosen set screws that hold the gears in place. Do steps 1-6 in reverse to put the hook gears back in place again