Last night I was trying to use the Pfaff 60 treadle, I adjusted the top and bottom tensions trying to get a nice stitch. Alas nothing was working.
It wasn't breaking the thread, but the top thread tension was just too loose; I could pull thread out easily on the back side of the pieces I was sewing.
Finally at my wits end, I changed the needle and put Aurifil #50 thread in it top and bottom; it solved the tension problems, after all that its sewing like it should. Gertrude was being a very stubborn German lady, she wanted a different thread.
Sharon in Texas