Tammi has a really well done video about how to rebuild your tension. Parts are available from sew-classic or other on line places.
https://www.youtube.com/watch?v=kzFX...AyBQ2l-Mzkw7ew
I don't know if that machine has plastic or metal gears. You might check to see if it is plastic gears. It may be that the zz timing is off. You will need someone who knows how to do the zz timing to fix that.