Symptoms
- Handles shake noticeably during use
- Vibration increases at higher throttle
- Hands feel numb after short use
- Visible looseness in the shaft or head
Likely causes
- CommonUneven line length on the spoolLine that's worn unevenly on each side throws the head out of balance.
- CommonLoose engine mounting boltsVibration over time can loosen the bolts holding the engine to the shaft housing.
- PossibleDamaged or bent trimmer headImpact damage to the head housing causes it to spin unevenly.
- PossibleWorn drive shaft couplingWear at the flexible shaft coupling adds play and vibration.
- Less commonCracked or loose handle mountsVibration-dampening bushings can wear out or crack over time.
What to do
- Shut off the trimmer and check that both trimmer line ends extend to roughly equal length.
- Bump the head to feed fresh, evenly balanced line if one side is noticeably shorter.
- Check and tighten all visible bolts along the shaft, engine mount, and handle.
- Inspect the trimmer head housing for cracks or bent sections and replace if damaged.
- Check the flexible drive shaft coupling for excess play if the trimmer has a curved shaft design.
- Inspect handle vibration-dampening bushings for cracks and replace if worn.
- Test at idle and full throttle; vibration should be minimal once line is balanced and fasteners are tight.
Tools and parts
- Wrench set
- Replacement trimmer line
Trimmer head assemblySearch: “trimmer head replacement”
Drive shaft couplingSearch: “string trimmer drive shaft coupling”
When to call a pro
If vibration continues after balancing the line and tightening fasteners, have a small-engine shop check the drive shaft coupling.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.