Trimmer Plus String trimmer head won't spin: Common Causes & How to Fix
1String Trimmer Drive Shaft
Most Common Solution
Repair Instructions:
The drive shaft is a long, bendable shaft that connects the clutch to the trimmer head. It spins the head for cutting. If the drive shaft breaks, the head won't turn. The drive shaft can't be fixed - if it's broken, you have to replace it. That long flexible shaft delivers power to make the head rotate. Check if the drive shaft is cracked all the way through or visibly damaged. Any breaks mean it needs a complete swap out. Trying to mend a broken drive shaft won't work. The shaft has to be in one, undamaged piece to spin the trimmer head. A broken drive shaft that's snapped in two can't engage the head.
How to Replace String Trimmer Drive Shaft
- Disconnect the spark plug wire from the spark plug to prevent accidental starting.
- Remove trimmer head and debris shield to access drive shaft. Consult manual.
- Remove clutch by detaching mounting bolt and sliding off shaft. Note orientation.
- Loosen and remove drive shaft housing screws using appropriate-sized screwdriver.
- Carefully pull drive shaft out from trimmer housing. Inspect for damage.
- Clean trimmer housing bore and new drive shaft using compressed air to remove debris.
- Apply lubricant to new drive shaft per manufacturer recommendations to ease installation.
- Insert new drive shaft into trimmer housing. Rotate shaft to engage gears.
- Replace housing screws and tighten securely. Be careful not to strip.
- Reinstall clutch onto drive shaft in the noted orientation and replace the mounting bolt.
- Replace debris shield and trimmer head. Ensure proper alignment.
- Reconnect spark plug wire to spark plug when complete.
- Test trimming operation to verify smooth drive shaft rotation and operation.
2String Trimmer Throttle Cable
Common Solution
Repair Instructions:
The throttle cable links the throttle trigger to the carburetor. Pulling the cable opens the carb throttle to speed up the engine. If the cable breaks, the engine won't rev up and the trimmer head won't spin. A broken throttle cable needs replacement. That cable is key for controlling engine speed. Check if the cable is snapped or visibly damaged. Any breaks mean it needs a swap out. A broken cable can't activate the throttle on the carburetor. This prevents revving the engine and engaging the head. Replacing the damaged cable restores the connection from trigger to carb. Having an intact throttle cable is crucial for accelerating the engine and getting the head spinning for cutting.
How to Replace String Trimmer Line
- Disconnect spark plug wire from the spark plug to prevent accidental starting.
- Remove spool cover to access the trimmer head, if equipped. Consult the owner's manual.
- Unwind any old string remaining on the spool and remove it completely.
- Clean debris from head and spool using a small brush or compressed air.
- Measure proper length of new line per the manufacturer’s instructions, usually 15-20 feet.
- Insert one end of line into anchor hole in the spool and wind line evenly and tightly around the spool.
- Leave 4-6 inches of line extending from each side of the spool.
- Adjust trimmer head to release the additional line if needed. Refer to the owner's manual.
- Replace spool cover if removed earlier. Ensure it is securely attached.
- Reconnect spark plug wire to the spark plug when finished.
- Start trimmer and tap head on ground to release line to operating length.
3String Trimmer Trimmer Head
Common Solution
Repair Instructions:
If the threads on the drive shaft are stripped, the trimmer head won't stay attached to the shaft. When that happens, you'll need to replace both the head and the shaft. Damaged threads prevent solid connection. Check the shaft's threads closely for any stripping or wear issues. If the threads are compromised, neither the head nor shaft can be salvaged. Trying to reuse a shaft with bad threads risks the head disconnecting during use. For safety, always replace both components together when the threading is damaged. Installing a new head paired with an undamaged shaft will restore good function. Properly mating threads are crucial for the head and shaft to stay connected while spinning. Replace any parts with thread damage to ensure safe, solid attachment.
How to Replace String Trimmer Head
- Disconnect spark plug wire from the spark plug to prevent accidental starting.
- Remove any covers or shields around the trimmer head. Consult the owner's manual.
- Loosen trimmer head bolt using an appropriate-sized wrench or socket.
- Unscrew trimmer head counterclockwise to detach it from the shaft.
- Discard old trimmer line remaining on the spool. Clean debris from the head.
- Feed new trimmer line through eyelets per line capacity of the new head. Refer to instructions.
- Wind trimmer line evenly around the spool in the direction indicated on head.
- Thread trimmer head onto shaft clockwise until tight and properly aligned.
- Tighten trimmer head bolt securely using a wrench or socket. Do not over tighten.
- Release trimmer line to proper length by tapping the head on the ground.
- Reinstall any covers or shields removed earlier.
- Reconnect spark plug wire to the spark plug when finished.
- Start trimmer to test proper string advance and cutting.
4String Trimmer Clutch
Repair Instructions:
The clutch connects to drive shafts that attach to the trimmer head. If the clutch is worn out, it can't engage the shafts to spin the head. You might be able to clean and fix the clutch assembly. But since swapping the clutch is pretty easy and cheap, replacing it may be better. The clutch has to engage the drive shafts for cutting. Check if the clutch seems excessively worn or is visibly damaged. If the clutch can't engage properly anymore, consider replacing the whole piece. Installing a brand new clutch ensures solid shaft engagement to rotate the trimmer head. A worn clutch that won't engage the drive shafts will stop cutting from happening.
How to Replace String Trimmer Clutch
- Disconnect spark plug wire from spark plug to prevent accidental starting.
- Remove clutch cover to access the clutch assembly. May require trimmer head removal.
- Mark current clutch orientation before disassembly. This will help during reinstallation.
- Remove clutch mounting bolt using appropriate sized wrench or socket.
- Remove clutch assembly from the trimmer shaft. Be careful not to lose parts.
- Clean trimmer shaft and clutch area using compressed air or rag to remove debris.
- Install new clutch on shaft oriented the same as the old clutch.
- Replace clutch mounting bolt and tighten per manufacturer's specs. Do not overtighten.
- Reinstall trimmer head and ensure proper alignment with clutch.
- Replace clutch cover and any parts removed for access.
- Reconnect spark plug wire to spark plug when complete.
- Start trimmer and test operation to verify smooth clutch engagement.