Let's take a look at the outside first.
|When you're sewing, the clutch would look like this.|
|When you're winding a bobbin, push the clutch in on the indentation.|
|Here's the top shaft of the bobbin winder.|
|Here's what the bobbin winder looks like underneath.|
Before you do anything else, check to make sure that the rubber O-ring (or tire) on the big round hub is in place, and is in good condition. It should be supple, and have no cracks. This can easily be replaced, and usually costs less than a dollar.
Also (as Ryan pointed out below), you'll want to make sure the spindle will turn easily. If it's frozen, you can try two things. First, I usually put some WD-40 in the cracks and work it until it's loose. Always blow the WD-40 out with an air compressor or canned air. Then re-oil. If that fails, you can pop the c-clamp off, disassemble the bobbin winder, clean it, and put some oil on the shaft directly. Then put it back together.
Next, we'll take a look at the inside of the clutch. You can carefully pry off the rocker with a screwdriver.
|Inside the handwheel, you'll see the center shaft, and the notches along the outer portion of the handwheel.|
If the notches are damaged, the handwheel would need to be replaced. If that's the case, you'd be better off putting your money into a new sewing machine.
|This is what the underside of the rocker looks like.|
If the metal clip or the plastic that holds the metal clip are broken, it would need to be replaced. Once again, you may be better off putting your money into a new sewing machine.