Check your tension again. There could be something within it causing tightness in the thread after a while. Check the
spring on the tension, it may have a burr. Have you put a drop of oil[just a bit] on the bobbin holder and run it a
little.

I have a Brother pq1500s there are 3 thread quide holes. Try only using 1 & 3 skip the middle one

my friend had this problem, it was the tracks that needed a rub down, she just used batting to rub off built up dust from the previous quilt.

is your Brother a long arm? I have a long arm that hates Sulky thread--just shreds it so fast! Also, older thread sometimes frays, especially if it's cotton. Totally rethread and try the next size up needle. When my top tension is a little tight, it also can cause shredding. And I've also noticed that when I do a batik quilt, especially with batik backing, I have to loosen the roller tension to prevent threading. Good luck! So easy to get super frustrated when your machine is demented. So sorry about the loss of your husband.

If it has been raining a lot, the high humidity will uncoil the strands of the thread. I had to change to Gutterman and that stopped the problem.

I also have that machine. Same problem. I have sent to the repair man time and time again sometimes not even taking from the shop before I tried it again. Still doing it. I am sure there is some sort of burr underneath . Sews fine with straight stitching but when I try to do free motion slowly (as around a motif) it shreds. So I have sent it back yet again. Have also tried new needles (as recommended by the machine shop) new cottons. will be interesting to see what repair man has to say this time.

Doctor Bob at Superior Threads has some wonderful information about threads, tensions, etc. I would suggest that you contact Superior Threads about the problem. I use a lot of their thread and never have problems when I follow the instructions. I also am careful to clean lint out of my machine frequently. I oil the hook and race mechanism when the maintenance light comes on as well. I hope you get your problem solved soon. I am sorry for the loss of your husband. I know that turning attention to something pleasurable will ease your grief. Do you have a friend who could help you.

I had a smal burr on the edge of the hole the needle goes down thru. I used really fine sandpaper and removed it. I needed a magnifying glass to see it. Try a different brand of thread? Different type of needle? Good luck this is so frustrating.

Check your bobbin case to be sure there isn't a burr or hole in the edge of it. This is a common problem with some machines. It often happens when you break a needle. It that's the case, you can take a very, VERY, fine sandpaper and go over the burr until you can get to your dealer for a new bobbin case. This problem would definitely cause thread shredding. You may also want to watch the thread as it feed off of the spool to be sure it isn't getting hung up on something which would cause the shredding. Hope you find a fix soon.

You didn't mention the size needle you are using...try a 90/14 topstitch. That may fix your problem.