If you will take a nice long look at your bobbin case, you will find that there are indeed two screws on the outside, one large and one small. The large one is for adjusting your bobbin tension. I don't know what the small one is for, but I don't see how it can have anything to do with the backlash spring.
On the inside, there is a thin piece of metal, that is slightly bent and it is removable. It looks like a perforated washer. THAT is your backlash "spring" or "brake". THAT is what controls backlashing.
It can't be flat, or it won't work right. They DO wear out. You can rebend it so that the "spring" is back. I keep these in stock for both my longarm and my sewing machines.
How your thread spools off the cone also contributes to the amount of backlashing you will experience. I don't typically have any trouble with backlashing myself, until my backlash spring is worn out, but the magnetic core bobbins (Magna Glides) totally and completely eliminate this issue, because the backlash spring is removed, and the magnetic core does all the controlling.
It's much more precise.