I also have a Brother xr40 with the same problem. No matter where the tension dial is at, there is no upper tension at all. Please tell me how to fix this. I have cleaned out all dust and lint but don't know what else to do. Can someone offer some suggestions please?
Thank you!

Meri, December 2009

Ken,
It worked! Thank you sew much!!!! I'm quilting again! It apparently needed flossing through the tension discs and I had forgotten to try that. I'll have to drag out the old machine and see if it'll work on that one too.
Maggs, thank you for helping out. You have no idea how much I rely on my sewing machine- almost as much as the coffee pot! Ok, it's a toss up! lol
Thank you both!!!

Meri, December 2009

Hello Meri,
Start at the beginning, make sure the presser foot is up and thread the machine, top tension about 4 or 5, make sure there is no lint stuck between the tension discs because it can build up sometimes, make sure the bobbin is in the correct way round, very easy to slip up, pull the thread through the bobbin case so there is some resistence, if it is too loose tighten the screw on the bobbin case about a quarter of a turn clockwise at a time and test sew.
Ken

drivewithken, December 2009

its usually the spool thats the problem if the stitching is lose have a look at the case see if thats too lose, hope this helps

maggs, December 2009