Bottom (bobbin) thread suddenly loosens

Good morning,

A few steps to help you troubleshoot:

1. Bobbin in the right direction: when looking at the bobbin in the bobbin case, pull the thread tail. The bobbin should turn clockwise.
   
   
2. One of the biggest causes of what you describe is simply a burr/rough spot on the needleplate or hook.
   
   Remove the needleplate from your machine and inspect the opening for any rough spots... run your finger over the area to feel for any sharp bits. If you discover some rough spots, they can be smoothed using a fine emery cloth. Use this gently - don't want to distort needle opening, just smooth the roughness.
   
   If no rough spots on needleplate, open the bobbin cover and turn the handwheel towards you until the hook (little pointy part of bobbin area) is towards the bottom of the machine. Run your finger over the point to feel for any rough spots. Again - a fine emery cloth can smooth this. Be VERY careful to not flatten the hook - just a little smoothing to get rid of rough bits. Too much can ruin the hook. If you're uncomfortable with this, don't hesitate to take to your Pfaff tech and point out the rough bits.
   
   
3. Hold the bobbin case/bobbin between finger/thumb, making sure you're not pressing on the bobbin tension (little flat metal piece on side of case). Pull the thread smoothly out of the bobbin case to see if you feel any little glitches. If you do, there may be a bit of fuzz/broken thread trapped under the bobbin tension.
   
   You can loosen the large setscrew on the side of the case to allow you to blow out whatever may be trapped.
   
   
4. While your top thread may appear fine, there may be a bit of fuzz or broken thread wrapped around the take-up lever. This would interfere with the smooth feeding of the upper thread, also causing an inconsistency in the bobbin.
   
   Use a flashlight and look down into the top of the machine/takeup lever area. You may be able to see a bit of thread and remove it. If you can't see an offending bit, try "Flossing" your upper thread path by grasping the thread close to the spool and after it comes out of the needle. Run the thread back and forth through the thread path to see if you can dislodge anything
   
   
5. If none of the above help, we'd suggest you have your local Pfaff authorized tech take a look. It's always a good idea to take your machine to it's respective authorized service person as they'll be the ones to know the most about it and have access to any repair parts.

Please don't hesitate to respond if you need further help or clarification.

Happy sewing,
Kim & Linnette