The purpose of the anti-backlash spring is to slow down the spinning of the bobbin as it first begins to sew and prevents the bobbin thread from over-spinning when the machine comes to a sudden stop.
Video | Anti-Backlash Spring
The anti-backlash spring is a thin, blue disc located at the bottom of the bobbin case.
The purpose of the anti-backlash spring is to slow down the spinning of the bobbin as it first begins to sew. This reduces the formation of thread blobs on the back of the quilt. If you hold the bobbin case and gently press on the bobbin, you should notice a small movement in and out. If this movement is not present, it is an indication that the disc is worn and should be replaced. The Anti-Backlash spring is a thin metal piece found in the bobbin case. This prevents the bobbin thread from over-spinning when the machine comes to a sudden stop. It should be removed periodically for cleaning as lint will collect behind it and degrade performance.
There are two types of bobbin cases, Seiko and TOWA. Your machine comes with a Seiko case and replacement cases are TOWA brand. The two brands have two different types of anti-backlash springs. Use the spring that fits your bobbin case
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TOWA Bobbin Case Anti-Backlash Spring The TOWA bobbin case uses an anti-backlash spring that has 2 spring arms.
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Seiko Bobbin Case Anti-Backlash Spring The Seiko bobbin case uses the solid or “football” anti-backlash spring. |
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When to Change the Anti-Backlash Spring
Change your anti-backlash spring when you can press down on the bobbin in the case and there is no bounce back. Some amount of scraping is normal. You should also change the spring if the tabs (circled below) are bent. The tabs that fit into the bobbin case are different sizes and in different locations and therefore, are not interchangeable.
How to Change the Anti-Backlash Spring 
- You will need a flathead screwdriver or tweezers.
- Remove the bobbin and then use the tweezers to remove the backlash spring.
- Clean out the bobbin case.
- Insert the tabs of the anti-backlash spring into the slots on either side of the inside of the bobbin case
- Use tweezers to place one of the tabs in one of the slots.
- Slightly blow the middle so the other tab will fit but be careful not to bend or damage the spring as you insert it. Make sure the bow in the spring is up.
Video | Cleaning under the Anti-Backlash Spring