Sandy if you didn't take the whole bobbin case out do that too, lots of lint gets under there. Some of the things I do ....bobbin case first, clean tension discs for lint, be sure and do this with a small brush or dental floss, just a tiny bit can get in there and really screw up a machine, re-thread the machine, new needle and new bobbin. Sometimes it's just the bobbin itself that in some way was wound wrong. If all that fails, I start from zero on the tension adjustment and then keep turning it tighter just a little at a time, sew a little distance and check it, turn some more, sew, etc. and see if it will reset itself that way. Maybe one of these will help.