I've read many times that the spring serves to put tension on the thread as the needle ascends, which then prevents skipped stitches. I'm hoping the broken spring is the culprit behind the skipped stitches issue on our 29-4...the machine is definitely skipping more stitches now that the spring has completely broken off...so fingers crossed! However, my friend's 29-4 also has a broken paddle spring yet infrequently skips stitches.