Which tension is possibly broken? There are two a top and bottom (the bobbin). Have you cleaned the machine? Take a lint brush that came with your machine and brush out the tension disks GENTLY. See if you get any lint or thread out. What thread are you using? The thread I get at a dollar store I find dirties the machine alot a friend of mine uses serger thread if she is sewing alot of dresser for weddings and it works great. Hopefully that works for the upper tension. I do not try to work on the bottom tension. Do you have a service store near you? Take the machine to them and see what they say and what the repair may cost. Good luck

It's the upper tension knob. The part with the numbers moves separately from the topmost part (the smaller knob that holds in the part with the numbers.) I would have thought that those 2 parts should move together. If I loosen the smaller knob too much, the numbered knob spins without doing anything.

Also, I'm wondering if there's a pants hemming attachment that can be put on this machine.

The brother website doesn't list this machine - guess it's too old?

Thanks.