I had a Juki bobbin thread breaking problem.
 

I wanted to post this for maybe someone searching for a solution to the same problem. I would be sewing and the bobbin thread would break. It looked like it was looping out of the bobbin case at the slit. I used a new bobbin, changed needle, etc. Still would break after a few inches of sewing. I had a new bobbin case so thought why not. I put the bobbin in the new case and it sewed just fine. I compared the old bobbin case to the new one and barely detectable I could see a slight dent at the slit of the old bobbin case. I guess I dropped it or needle hit it just right. I saved a trip and cost of repair by having the new one and trying it out first. I buy most of my accessory parts from Wawak online. I keep all easy changeable parts on hand.

And those metal parts seem so sturdy, too. :(

Thanks for posting this.

hugs,
charlotte

Good reminder. I think I need to change my bobbin case on my Janome.
Been having a lot of thread breakage lately. Cleaning and oiling doesn't
seem to help.

Thank you onebyone! I had a similar problem with a Juki bobbin, but it was an obvious bash not a small dent. I try to be ultra careful with those bobbins now.