Tension, Is it getting to you?
The stress, eegads the stress of all this tension crud! Is there any relief?
Having issues with the tension on your sewing machine? Not uncommon at all, even with new machines. I bet it’s driving you nuts.
Did you know that if you were a sewing machine, you could just lift your foot and all your tension would disappear! 
On a more serious note, I really do have a have a few ideas for you to sort out your tension woes. First, clean clean clean, especially on an older machine. In this file, there are generic instructions for flossing the tension assembly to help clean it.
On many vintage machines, it’s not uncommon for the tension discs and other tension parts to be coated with a layer of grime, goo or even rust. I take the tension assembly apart and clean and polish every piece before I reassemble and recalibrate the tension. 
These shiny, new looking parts are from a 60 year old machine. The thread glides through more smoothly and the tension adjusts more evenly when this is done.
Here are some more resources to help with your tension woes:
Adjusting Sewing machine tension file
More tension adjusting tips:
Thread nest, Wads, Tangles in the bobbin area & under the fabric- How to fix
Slanted Stitches - why the stitches aren't straight and what to do abut it.
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Has this site been helpful?
That's it, I'm raising my feet off the ground!
I think a lot of people have tension issues because they're afraid to fiddle with it, especially the bobbin tension.
I use a TOWA gauge to set my bobbin tension, and then simply adjust the upper tension to match, and have never had any trouble at all.
Thanks for tutorial. helpful
I have adjusted my 201-2 needle and bobbin tension as indicated by the manual. When I pull on the threads at the foot I can definitely feel the tension difference as I tweak the dial or turn the bobbin screw. However, it seems like the stitch remains the same no matter how I set the tension. The stitch is good - but I figured that I would be able to tweak it more and see more of the tell-tale signs of loose thread tension - I can't seem to change the quality of the stitch at all by altering the tension... Am I crazy?
Brother VX880: I have attempted to adjust the upper (about 4) and the lower tension, using bobbin drop method. The machine makes about 4 stitches and then the needle begins to bind. I find that the thread has tangled on the shuttle cock, and is so tight, I have to remove the shuttle to remove the thread. It does the same whether one or three layers of cloth. Any suggestions?
Try this:
Thread Nests, Wads, Bunches, Knots, Loops & Tangles Under the Fabric in the Bobbin Area- How to fix it