Symptoms
- Grease visible around the gear head housing
- Grease residue on the ground under the head after storage
- Grinding noise from the gear head suggesting low lubrication
- Grease appearing dark or gritty
Likely causes
- CommonOverfilled gearbox from a previous serviceAdding too much grease can force excess out through the seals under heat and pressure.
- CommonWorn output shaft sealThe seal where the shaft exits the gearbox wears out over time and years of vibration.
- PossibleCracked gearbox housingImpact damage can crack the housing and let grease escape.
- Less commonContaminated grease breaking downWater or debris intrusion can thin out grease, making it more likely to leak.
What to do
- Check the grease level in the gear head via the fill plug; only fill to the level specified in the manual, usually about two-thirds full.
- Wipe away external grease and monitor over a few uses to see if leaking is ongoing or was just residual from a recent fill.
- Inspect the area around the output shaft where it exits the housing for signs of a worn seal.
- Look over the gearbox housing itself for cracks, especially after any impact.
- If the seal is worn, this typically requires a small-engine shop to replace, since it involves partial gearbox disassembly.
- Use only the grease type specified by the manufacturer, since the wrong grease can break down and leak more easily.
- Replace the entire gear head assembly if the housing itself is cracked.
Tools and parts
- Grease gun or manufacturer-specified grease
- Rag
Gear head greaseSearch: “trimmer gear head lubricant grease”
Gear head assemblySearch: “trimmer gear head replacement”
When to call a pro
If the output shaft seal is worn or the housing is cracked, a small-engine shop can replace the seal or gear head assembly.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.