That's a sign the blade is likely unbalanced, bent, or loose. You need to stop using it and check immediately.
- Safety first. Remove the battery pack.
- Tip the mower. Carefully lay it on its side with the air filter and motor housing facing up.
- Inspect the blade. Use a block of wood to keep the blade from turning, then try to turn the blade bolt with the provided wrench. It should not move. If it's loose, tighten it securely.
- Look closely at the blade for bends, nicks, or cracks. A bent blade will cause severe vibration.
IF THAT DIDN'T WORK: The blade adapter or spindle might be damaged from hitting a solid object like a rock or root. If the blade is tight and looks straight but vibration persists, the internal spindle may be faulty.
HEADS UP: Never operate with a damaged or loose blade. It's dangerous and can break, causing injury or damaging the mower. Replace damaged blades only with an official Greenworks replacement blade.