The easiest fix it to buy a new tension unit from sew-classic and put it on. You release the set screw and pull out the old tension. Then you put the new tension unit in and tighten down the set screw. You can buy a parts machine as long as it is similar and transplant the tension the same way. You can some times use a part from one tension to another but you can get into whether or not the pin in the center hits the bar like it is suppose to.