The feed dogs can become worn or damaged enough to need replacement, but it will show. I'm guessing it's something else. Have you had the needle plate off and cleaned under there? Can you detect movement of the feed dogs according to stitch length setting? Even with a reasonably clean and lubricated machine I would start with a thorough cleaning, oiling and investigating parts down there. Pay particular attention to all parts involved from stitch length lever to feed dogs when oiling, wham the machine and repeat a few times. I have had machines stuck on zero stich length because of frozen up parts, and it's not always that obvious where the problem is.
Other very basic things to check is of course presser foot lever down (silly thing to forget, usually only when the darning foot is on) and presser foot tension screw.
Last edited by Mickey2; 03-05-2017 at 09:20 AM.