Symptoms
- Loops of thread visible on the top or bottom of the fabric
- Fabric puckers along the seam
- Stitches look tight on one side and loose on the other
- Tension was fine on a different fabric or thread
Likely causes
- CommonTop thread tension set too tight or too looseThe tension dial controls how much resistance the top thread feels, and it needs adjusting for different fabrics and threads.
- CommonIncomplete threading through the tension disksThread that slipped out of the tension disks won't get proper resistance no matter the dial setting.
- PossibleBobbin tension incorrectA bobbin case tension screw that's been bumped or needs adjusting affects the bottom thread's pull.
- PossibleDifferent thread weights used on top and bobbinMismatched thread thicknesses can throw off the balance even with correct settings.
What to do
- Rethread the top thread completely with the presser foot raised, making sure it seats fully in the tension disks.
- Start with the tension dial at the manufacturer's default setting (often marked or around the midpoint) and adjust gradually while testing on scrap fabric.
- Check that the same weight and type of thread is used on both the top and bobbin.
- If the bobbin thread seems off, do a simple bobbin drop test: hold the thread and let the bobbin case hang, and it should drop slowly and evenly, not free-fall or stay stuck.
- Adjust the bobbin case tension screw only in very small increments if it's confirmed to be the issue, since it's easy to over-adjust.
- Test stitches on scrap fabric after each change, checking both sides.
Tools and parts
- Scrap fabric for testing
When to call a pro
Take it to a sewing machine technician if tension stays uneven after rethreading and dial adjustments, since the tension assembly itself may need cleaning or repair.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.