feline fanatic

Here is a link to a longarm supply place that shows a picture of what the backlash spring looks like when it is loaded in the bobbin case. http://www.longarmsupplies.net/bobbincasetowa-1.aspx You do not wrap your thread around it. The premise behind it is that the circular inner part that can best be described as "arms" lifts up a wee bit and puts friction on the bobbin to keep it from spinning. Backlash happens when changing directions abruptly or stopping abruptly.

If it isn't working correctly then you can have several issues going on.
The spring is inserted incorrectly
The arms need to be bent out a but so they are once more putting friction on the bobbin
The spring needs to be replaced
Your bobbins aren't loaded with the same tension throughout or insufficient tension, you may have an issue with your bobbin winder. Do the bobbins feel spongy or firm when you press the thread? Spongy = bad tension on the wind. Firm is good.

These are the steps I would take to try and figure out the issue (assuming you have already done the aforementioned "squeeze" test on your wound bobbins).
1. Check to make sure your backlash spring is there
2. If so, remove it bend those arms out a wee bit and reinsert
3. If that doesn't work I would try ordering a new spring, they are relatively cheap so you may wish to add on some other supplies to your order as the shipping and handling will probably cost more than the spring.
4. Remove the backlash spring and try Magnaglide prewound bobbins and see if that doesn't solve your backlash issue.

Work around is slow down! Especially when changing directions.

quiltingshorttimer

adding to what Feline has said, i once had a bobbin that I wound way too tight--still not sure what happened, but the thread would not pull off consistently. Do you use a Towa gauge? it will help a lot with checking that each bobbin is consistently wound and pulling off without problems. also, besides the bobbin spring(which doesn't look at all like a typical spring so don't let that confuse you) you might check that your thread is setting under the tension arm of the bobbin ok--it's possible that it's worn out. I do sometime use the magic genie "washers"--you don't use a bobbin spring with them, but i truly believe the bobbin spring works better. good luck--machine problems are SO annoying!