String Trimmer Gearbox Replacement

String Trimmer Transmission, Brake, Clutch & Gearbox Parts

The transmission, clutch, and gearbox in your string trimmer are what transfer engine power to the cutting head. When the clutch slips, the transmission won't engage, or the gearbox grinds, the trimmer stops cutting — even if the engine runs fine. These parts take constant torque abuse, especially on brush-laden jobs or when the head jams.

OEM transmission and clutch assemblies ensure proper engagement ratios and safety. Aftermarket gearbox parts often wear faster and can strip threads on the drive shaft. Enter your trimmer model number to find the exact transmission brake, clutch shoe assembly, or gearbox replacement your machine needs.

• Clutch shoes not engaging: trimmer head spins slowly or not at all; engine running at full throttle
• Transmission slipping: power loss when cutting thick weeds; RPM drops under load
• Gearbox grinding or noise: metal-on-metal sound during operation; gear teeth stripped
• Drive shaft broken: straight-shaft models; severe vibration or complete loss of head rotation
• Brake won't hold: head keeps spinning after engine stops; safety hazard

String Trimmer Transmission & Gearbox: Common Questions

What's the difference between a clutch and a transmission in a string trimmer?

The clutch is a friction-based mechanism that engages when engine RPM rises above idle — it connects the engine crankshaft to the drive shaft only when power is needed. The transmission (or gearbox) reduces engine speed and increases torque before it reaches the trimmer head. Most gas trimmers have both: the clutch engages at higher RPM, and the transmission steps down the speed. When the clutch slips, the engine screams but the head barely turns. When the transmission fails, you'll hear grinding or feel complete power loss.

Why does my trimmer head spin slowly even though the engine runs at full throttle?

A slipping clutch is the most common cause — the clutch shoes aren't making full contact with the drum, so power bleeds away as heat. Less common: a worn transmission with stripped gears, or a drive shaft bearing that's seized and creating drag. Start with an OEM clutch assembly. If the head still spins slowly after replacement, the transmission gearbox or drive shaft bearing is likely damaged.

How do I know if my trimmer's gearbox is broken?

Metal grinding sounds, vibration, or complete loss of head rotation point to internal gear damage. On straight-shaft trimmers, a broken drive shaft creates severe vibration and the head won't turn at all. Gearbox repairs aren't typically field-serviceable — replacement with an OEM gearbox assembly is the standard fix. Use your model number to confirm the exact gearbox type; FS, 128LD, and trimmers all have different gearbox designs.

Can I replace just the clutch shoes, or do I need the whole clutch assembly?

Most OEM clutch kits include the shoes, springs, and drum as a complete assembly — that's the safest replacement. Individual clutch shoes are occasionally available, but matching the spring tension and shoe angle is critical for smooth engagement. An OEM clutch assembly eliminates guesswork and model-specific fit and performance. Enter your trimmer's model number to see if shoes-only or full assembly is the correct part.

Shop String Trimmer Gearbox Replacement Online

Finding the right gearbox replacement for your string trimmer is needed for maintaining its performance. Our online store offers a variety of compatible string trimmer gearbox replacements. Enjoy the convenience of same-day shipping, ensuring your parts arrive quickly. Use our model or part number lookup to find the exact match for your equipment. We also offer a No-Hassle 365-Day Returns policy and a Price Match Guarantee, making it easy and affordable to keep your trimmer running smoothly. Address common issues like a non-spinning trimmer head by replacing a broken gearbox. For tips on fixing string trimmers, visit our String Trimmer Repair Help page. Browse our selection and order your string trimmer gearbox replacement online today!

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Use Your Model Number to Find the Right String Trimmer Parts

Check the main housing near the engine or the label along the shaft for your string trimmer's model number. You may need to brush away dirt or remove a cover to read the complete number, including letters and dashes. Enter it in the search bar to filter this page to the parts that fit your model. The model number identifies the entire trimmer, so it narrows the catalog for gearboxes, clutches, drive parts, and other associated parts, not just one replacement. Matching the number before you order helps confirm the correct design and specifications for your machine. That means fewer wrong orders and a faster repair.