Last week, I bought my first vintage sewing machine. I spent several days cleaning it up. I didn't want to take the thread tensioner apart. It seems too complex. However, when I tried out the machine the thread didn't want to flow smoothly through the tensioning mechanism.
With some help from a couple of really good Youtube videos, I broke it all down and cleaned out a good deal of grit. I also cleaned up the little thread holder part of take up spring, which was rusty, with emery paper. I put it back together, and everything seemed to be working pretty well.
Today, I did some real sewing with the machine. All in all, this is the best machine I have every used. However, every once in awhile the thread would break because it got stuck/too tight at the tensioner. It also seemed to me that the tension dial would go from 2 (where I wanted it) to 1 or lower on it's own.
My gut tells me there is something wrong with the spring, but before I send for a new one, I thought I'd check with some of you more experienced people to see what your advice would be.