To rethread a typical bump-feed weed wacker, fully power the tool down, open the trimmer head, clear old line, wind fresh nylon line evenly in the direction marked on the spool, feed the ends through the eyelets, and reassemble the head. Confirm line diameter, cut length, and wind direction on the spool, head, or owner’s manual. Those details vary by model and head type, so a rewind that ignores the markings often fails to feed.
A weed wacker, also called a string trimmer, usually cuts with replaceable nylon line held in a spinning trimmer head. When that line snaps, welds together, or retracts inside the housing, the tool stops cutting even if the motor or engine still runs. Most consumer bump-feed heads can be rethreaded at home once you know the head type, keep small parts in order, and wind the spool the way the markings indicate.
Power Down and Protect Yourself First
Open the head only after the tool cannot start. A string trimmer head can still spin if power remains connected, and a spring under the cap can jump when the cover comes off. Treat the cutting head as live until you have removed the energy source and all motion has stopped.
Match the power-down step to the tool you have. On a battery model, take the pack off the handle or housing and keep it away from the work area so it cannot be clicked back in by accident. On a corded electric trimmer, unplug the cord from the outlet, not just from an extension lead that might still be live. On a gas weed wacker, release the throttle, switch the engine off, and wait until the shaft and head are completely still. Do not rely on the trigger alone. A bump against the switch, a residual charge, or a short pull on a starter can move the head while your hands are on the eyelets.
Give the job ordinary shop protection. Safety glasses or goggles belong on before you pry at a cap, because old line, grit, and a loose spring can fly toward your face. Close-fitting gloves help when you pull fused nylon out of an eyelet, but keep enough feel to handle small washers. Tie back loose clothing and hair, and keep bystanders and pets out of the immediate area even for a rewind. The tool is not supposed to run during this work, but the head still holds tension and sharp, broken line ends.
If the trimmer was just used, let hot plastic and metal cool enough to handle. A recently run head can be uncomfortable to grip, and warm nylon is more likely to smear or weld if you force it. Follow the owner’s manual for any model-specific lockout, parking, or storage step. When a gas unit has a fuel leak, a damaged switch, or a head that will not stop spinning promptly, stop and have a qualified small-engine or outdoor-power technician inspect it before you continue.
Identify the Trimmer Head Before You Rewind
Not every trimmer head is meant to be rewound like a classic bump-feed spool. Forcing that process onto the wrong design wastes line and can crack the housing. Look at the head itself before you cut new nylon.
A common bump-feed head has a rounded knob or button on the bottom. You tap that bump knob on the ground while the head is spinning so more line can slip out of one or two eyelets. The cap often shows arrows, plus and minus marks, or the words that tell you which way the spool turns. Inside, you will usually find a reel, a spring, and sometimes a washer or divider.
An auto-feed head may look similar from the outside but advances line with a clutch, cam, or centrifugal mechanism instead of a deliberate bump. Some of these still use a user-wound spool. Others are easier to service with a prewound cartridge. A fixed-line head has individual ports or slots around the rim. You push short, pre-cut lengths of line into those ports rather than winding a reel. A sealed cassette or factory cartridge is a drop-in spool that is not designed to be refilled; the whole cartridge is replaced when the line is gone.
Useful markings include the line diameter printed on the cap or spool, arrows for winding direction, a fill line on the reel, and labels that say how many line ends the head uses. Count the eyelets. One exit hole usually means a single-line setup. Two opposite holes usually mean dual-line. Extra ports around the rim often point to a fixed-line design.
Stop and change the approach if the head is a sealed cartridge, if pieces of the reel or spring are missing, or if the housing is cracked. Replacing the prewound spool or the entire trimmer head is more practical than improvising a rewind the parts cannot support. When the type is still unclear, use the markings on the head and the owner’s manual rather than assuming every weed wacker winds the same way.
Choose and Cut Replacement Line
Use nylon trimmer line sized for that head. The correct diameter is usually printed on the spool, the trimmer head, or the owner’s manual. Matching that marking matters more than picking a line that simply looks close. Line that is much too thick can jam in the eyelets, refuse to bump-feed, or strain the motor or engine. Line that is much too thin can snap as soon as it hits grass, slip through the spool, or feed so freely that it welds or unravels.
Shape is a secondary choice. Round line is common and usually easy to wind. Twisted, serrated, or other profiles are sold for different cutting feels, but they still have to fit the eyelets and follow the same winding rules. You do not need a special shape to rethread a standard head. If the old scraps are a different profile from the new coil, that is fine as long as the diameter matches the head and the new line is flexible enough to seat in the spool slots.
Cut length is not universal. Manufacturers specify different amounts for single-line and dual-line heads, and a larger spool holds more than a compact one. If the manual is missing, use leftover line as a template when a complete old length is still on the reel. Otherwise, cut a manageable piece, wind until the line sits even with the spool’s fill line or just below the rim, and stop before the wraps bury the eyelets or bulge past the flanges. Overfilling is a frequent cause of binding. Underfilling simply means you will rewind sooner.
Straighten a coil that wants to spring into loops before you start winding. Warm the line slightly in your hands if it is stiff from storage, but do not heat it with a flame or a heat gun. Nylon that has been baked or left in a hot shed can be brittle. Discard cracked, chalky, or flattened line rather than forcing it through the head. Nylon trimmer line is the intended cutting material. Wire, cable, or homemade metal substitutes can break, throw fragments, and damage the head; they are not a safe replacement.
Open the Head and Remove the Old Spool
Set the powered-down trimmer on a stable surface so the head faces up. Common bump-feed caps come off in more than one way. Some lids have snap tabs you squeeze inward. Some unscrew after you hold the housing still. Others use a press-and-turn lock. Look for arrows, release marks, or recesses for your thumbs before you pry. Do not treat one latch style as if it applied to every weed wacker, and do not force a cap that is clearly meant to rotate.
Expect a spring. When the cover lifts, that spring can jump out of the bump knob or the center post. A small washer or retainer may sit above or below the reel. Lay the parts out in the order they came off: cap, spool, spring, and any washer or divider. Photographing the stack with a phone before you disturb it can save time later, especially on a dual-line reel with a center wall.
Lift the spool straight off the post. Pull leftover line out of the eyelets from the outside if it will slide. Fused or broken nylon that is welded into an eyelet often needs to be pushed back inward, then picked out of the reel rather than yanked from the tip. Clear grit, grass packing, and melted beads from the eyelets and the cavity. A wooden toothpick or a plastic pick is gentler than a steel screwdriver, which can enlarge a worn eyelet and make later line snap.
Inspect the parts while the head is open. The spool should turn freely on its post once debris is gone. The spring should still have bounce. The bump knob should move and return. Cracks in the cap, a flattened spring, a missing divider, or eyelets worn into sharp slots are reasons to replace those parts or the whole head instead of winding new line onto a damaged reel.
Wind New Line Evenly in the Correct Direction
This is the core of a successful rewind. The line has to sit in even layers and travel the direction the spool expects. Winding the wrong way is a common reason bump-feed line will not advance. Crossed layers and an overfilled reel are the other usual failures.
Follow the marks on the spool
Look for arrows, molded text, or a winding diagram on the reel, the inner face of the cap, or the head housing. Wind in that direction. If one half of a dual-line spool has its own arrow, treat each half independently. Do not invent a default clockwise or counterclockwise rule when the marks are missing. If there are no marks at all, note which way the old line was wrapped before you strip it, or check the owner’s manual. When even that is unavailable, wind a short test amount, assemble the head, and see whether a bump releases line. If the line retracts or locks, unwind and reverse direction.
Seat dual-line and single-line correctly
A dual-line spool is often divided by a center wall, with a slot or hole in the middle of that wall. Fold a single continuous length of line at the midpoint, push the fold into that slot so both legs are equal, and wind each half into its own compartment. Some dual-line reels instead use two separate pieces, each anchored in its own hole or notch. A single-line spool has one anchor hole or slot and one winding path. Hook the end in that anchor so it cannot slip, then wind toward the open flange.
Keep enough free end on each side to reach through the matching eyelet after the spool goes back in the housing. Those tails should be long enough to handle, but not so long that they tangle while you are still winding. Many spools have small notches on the outer rim where you can park the tails temporarily so the wraps do not spring loose.
Keep the layers snug and even
Hold light, steady tension as you wind. Each wrap should lie next to the last one instead of stacking in a heap or crossing over earlier layers. If the line climbs the flange or jumps the divider, back up and lay that section down again. Snug is enough. Stretching the nylon hard can make it later contract, bind, or pull the tails back into the head.
Stop at the fill line or just below the rim. The reel still needs clearance to turn inside the housing, and the parked tails need a clear path to the eyelets. Overfilling and crossed line usually cause the head to lock, chatter, or refuse to bump. An uneven mound on one side of a dual-line spool can make one string feed while the other stays trapped.
Thread the Eyelets and Reassemble the Head
Hold the wound spool so the parked tails line up with the housing openings. Feed each line end through its matching eyelet from the inside out. On a dual-line head, the two exits are usually opposite each other; crossing the tails to the wrong holes will fight the wind direction and can keep the reel from turning. Pull the ends through until the spool can drop onto the center post without kinking the line against the rim.
Seat the spring and any washer in the same order you removed them. The spool has to sit on the post so the reel can still rotate. If the spring is cocked to one side, the bump knob may stick or the cap may not close. Lower the cover straight down, guiding the line ends through the cap cutouts if the lid has them. Close the cover until it clicks, locks, or is fully threaded, depending on the design. A cap that is only partly seated can fly off when the head spins.
Pull the outside ends so they are even and free of twists. Leave enough line outside to reach the edge of the debris shield, then trim the tips there after the shield is confirmed to be in place. That outside length is a starting point, not a required measurement. The shield is the real limit. Running a string trimmer without its installed debris shield exposes you to thrown line, stones, and broken nylon. Do not test or cut until that guard is on and secure.
Spin the head by hand with the tool still powered down. The spool should turn a little as you pull a tail, and the bump knob should move and return. If the reel feels locked, open the head again before you restore power. Binding at this stage is almost always a winding, overfill, or assembly issue, not a reason to force the motor.
If the Head Is Not a Standard Bump-Feed Spool
Some consumer heads never use the rewind sequence above. A fixed-line or quick-load head usually takes short, equal lengths of nylon pushed into ports until they catch. You cut those pieces to a length that matches the remaining stubs or the shield, insert them fully, and tug to confirm they are locked. There is no inner reel to wind, and bumping the knob will not pay out more line. When a piece breaks, you replace that piece.
A prewound cartridge or factory-wound spool is often the simpler path on auto-feed and some bump-feed designs. You open the head, drop in the matching cassette, route the factory tails through the eyelets, and close the cover. If the cartridge is sealed, do not split it to refill it unless the manufacturer clearly designed it that way. A cracked, incomplete, or sealed head that no longer holds a spring or reel should be replaced as a unit.
Not every auto-feed mechanism is user-serviceable beyond swapping the spool. If the head uses internal cams, a one-way clutch, or parts you cannot identify from the markings, stop rather than disassemble it into undocumented pieces. Replace the head with one specified for that trimmer if parts are missing or the housing is damaged. Do not substitute wire, cable, or shop-made metal cutters for nylon line in any of these designs.
Restore Power and Check That Line Feeds
Restore power only after the head is fully assembled and the debris shield is installed. Reinstall the battery, plug in a corded unit, or start a gas engine in a clear area using the normal starting routine from the manual. Keep bystanders, pets, windows, and loose gravel away from the first spin. The line ends will whip at full speed as soon as the head turns.
Bring the trimmer up to cutting speed briefly, then use the feed method the head was built for. On a bump-feed head, tap the bump knob lightly on bare soil or a worn patch of ground, not on concrete or stone if you can avoid it. You are checking that line can exit, not trying to empty the spool. An auto-feed head should pay out a little line on its own as it comes up to speed; if it does not, stop and reopen the head rather than revving longer. Trim any extra length back to the shield after the test if the tips extend past the guard.
Listen and look. Line that exits smoothly and stays balanced is the goal. If nothing comes out, if only one side of a dual-line head appears, or if the head chatters and the tool bogs without touching grass, shut the trimmer down and return to the rewind. A first start after rethreading is a function check. It does not guarantee the tool will cut like a new unit, and one bump does not always release a fixed amount of line.
Troubleshooting After Rethreading
Most failures after a rewind are mechanical. Wrong wind direction, crossed layers, overfill, the wrong diameter, worn eyelets, a missing spring, or line fused from heat explain the majority of “it still will not feed” complaints. Work through those causes before you assume the motor, battery, or engine needs repair.
Line that binds or will not exit is often wound against the marked direction or stacked so tightly that the reel cannot turn. Open the head and check the arrows. If the wraps look tidy but the spool still locks, remove a few layers. Line that retracts into the head usually means the tails were too short, the parking notches let go before the eyelets were threaded, or the spring is not returning the bump knob. Reseat the spring and leave longer working ends the next time.
Nylon that welds into a solid ring is a common field complaint after the line has been spinning inside a hot, packed head. Heat and friction can fuse touching wraps so the reel becomes a single lump. Cut the fused mass out, clean the eyelets, and rewind with even layers and a little less fill. Letting the head cool between long cutting sessions and clearing packed grass from under the shield reduces repeat welding, but it will not disappear entirely on a hard-used trimmer.
A bump knob that does nothing may be assembled without its spring, stuck with debris, or blocked by an overfilled spool. It can also mean you are working on an auto-feed or fixed-line head that was never meant to advance from a tap. Confirm the head type before you keep striking it on the ground. Repeated hard bumps on pavement wear the knob and can crack the cap.
Line that keeps breaking at the eyelet often points to a worn, sharp exit hole, line that is too thin or too brittle, or tips that were left so long they slapped the shield. Replace a gouged eyelet insert if the head has one, or replace the head if the hole itself is knife-edged. If the trimmer bogs as soon as the line touches thick growth, the line may be too thick for that unit, the head may be packed with debris, or you may be asking a light-duty tool to cut material it cannot handle. Clear the head and verify the diameter marking before you look past the cutting system. Carburetor, battery, and motor diagnosis are separate jobs and are not solved by another rewind.
When the housing is cracked, the spring will not stay seated, or a sealed cartridge has failed, replace the spool or the trimmer head rather than forcing more line into damaged parts. A clean rewind on a sound bump-feed head is usually enough to get a consumer string trimmer cutting again. The markings on that head remain the final authority for line size, wind direction, and whether the reel is meant to be refilled at all.
