Shredded thread
 

I have a Pfaff longarm. I have changed needles, quilt bar tension, leveled the machine, made sure there were no burrs anywhere, redid the bobbin....and my thread is still shredding. Help!
What am I missing??

What have you done with thread tension? Also, what thread are you using in top and bobbin? And what size needle? Is this a machine that is new to you?

It is used but new to me. Using sidnature 40 wt as suggested by a pfaff dealer. Needle size 100/16 inspira.

Have you had the machine work fine before, without thread shredding?
What is different now?

Try swapping out the thread for a different one.
Hopefully one that has been a success for you before.

Not a long arm but when I got my used PQ 1500 Nouvelle it shredded thread. I was so frustrated. I tried a lot of different threads/needle combinations and we seem to have come to terms. I know it is different for each machine. But, don't give up, keep trying different threads/needle combos.

Here's the thing. The previous owner could have been using a completely different kind of thread and adjusted the top and bobbin tensions to suit that thread. Typically what you want to do in a situation like yours is start by loosening the top tension. You may also have to loosen the bobbin tension. This video by Jamie Wallen provides a very good demonstration about how to adjust tensions.
https://www.youtube.com/watch?v=Q1mRhcquZTM

I have used Signature and it is a good thread. However, I have found cotton threads such as Signature and King Tut shred more easily on my machine than polyester threads such as Glide and Bottom Line. You may want to try a polyester thread to see if it works more easily for you.

If the fabric is not resting on the bed of the sewing machine, it will shred thread.
If you have been able to sew without problem, and now the problem is happening - what has changed (i.e. did you change bobbin, load new fabric, roll the quilt.... )
If you can, make sure you pull a long long length of thread off before rethreading, then slowly trace each and every step... make sure there isn't anything along the thread route that is off/rough, and then check the bobbin/bobbin case and race..
That's the best I can offer right now, please add more details to the story and then maybe some more thoughts will pop into my head.

When you are sewing high speed with a rotary hook, it doesn't like to sew from right to left. If it's shredding as it sews a straight line from right to left, that's just the nature of the beast. I don't know if your machine has a round shank needle or not, but if it does, you can turn the needle slightly to the right. It makes a pretty big difference.

If I'm using thread I know is older, I put a line of fine machine oil along the height of the cone.

I just skimmed through the replies to your question so I don't know for sure if this was mentioned but I found that a Topstitch needle solved a lot of my problems. I have the Pfaff 1200 and changing to that needle made a huge difference.