Overview
This aftermarket gearcase assembly is built to OEM specifications for string trimmers and brush cutters that rely on a geared lower drive. When the original gearbox develops excessive noise, heat, or lost motion, replacement is more practical than rebuilding the internal gears. This unit includes the housing, gears, and necessary bearings for a complete swap.
Key specifications
- Replacement gear head/gearbox assembly
- Includes housing, bevel gears, and bearings
- Pre-lubricated for immediate installation
- Direct-fit OEM-equivalent design
- Hardened steel gears for long service life
Compatibility
This gear assembly is designed for Toro trimmers and brush cutters as specified above. Verify the shaft diameter, thread direction, and mounting style before ordering.
Installation notes
With the trimmer powered off, remove the bump head or blade from the lower gear housing. Unbolt and slide off the old gearbox, noting the shaft engagement. Mount the new assembly, secure it firmly, and reattach the cutting head. Spin by hand to confirm smooth engagement before starting the engine.
Common questions
Q: Will this 308210008 gear case assembly fit my Toro 51977 trimmer, and is it the same part as 308210009 used on some Ryobi models?
Yes, this gear case assembly is compatible with the Toro 51977 as well as Toro models 51954, 51955, 51974, 51975, 51976, 51978, 51978A, and 51998. It also replaces 308210009 on certain Ryobi trimmers including RY4CSS, RY253SS, and RY34440/S430, so it’s commonly used across both brands when the shaft and drive connection match those listed models.
Q: My Toro 51978A head stopped spinning even though the engine runs fine—could the 308210008 gear case assembly be the part I need?
If the engine runs but the cutting head does not turn, or it turns inconsistently with grinding noise from the lower end, a worn or damaged gear case is a common cause. Replacing the 308210008 gear case assembly is often the correct fix when the failure is in the lower gearbox rather than the clutch, cable, or upper drive shaft.
Q: Do I need to grease or service this 308210008 gear case assembly after installing it on a Ryobi RY253SS or Toro 51975?
It’s a good idea to inspect the gearbox for proper lubrication during installation and follow your trimmer’s maintenance schedule afterward. If your unit has a grease point or serviceable gearbox design, using the correct gear lubricant periodically will help reduce heat, wear, and premature gear failure.
