Make the trimmer safe by removing the battery or unplugging it, then wait until the head has fully stopped. Open the trimmer head, take out the spent line or spool, and load compatible new monofilament line in the direction marked on the spool. Feed the ends through the eyelets, reassemble the housing cap, and confirm the line feeds evenly. Head design and line size vary by Dewalt model, so follow the markings and the tool manual when they differ from a generic bump-feed process.

What changing Dewalt trimmer string actually involves

A Dewalt weed eater is a string trimmer: a rotating trimmer head spins nylon monofilament line to cut grass and weeds. Changing the string is routine service, not a repair. You are replacing worn trimmer line so the head can cut again. You are not rebuilding the motor, shaft, or guard, and you usually do not need to replace the entire cutting head.

The same goal applies across common Dewalt cordless and corded trimmers. You de-energize the tool, open the head, clear spent line, load new line, close the housing, and check that the free ends exit the eyelets and can advance. What changes from one tool to another is the mechanism inside the head. Some heads use a reusable spool that you rewind by hand. Some accept a prewound spool. Others are quick-load designs that take a length of line through the head or spool, then wind both sides together. A few use short fixed pieces of line instead of a long stored coil.

That is why a generic video can look wrong even when your trimmer is working as designed. Bump-feed heads release more line when the bump knob taps the ground. Auto-feed heads try to advance line as it wears. Quick-load and fixed-line heads follow still another path. If the molded arrows, tabs, or spool graphics on your Dewalt head disagree with a tutorial, the markings on that head and the owner’s manual for that model should win.

Before you start, decide which job you actually have:

  • The line is short, fused, or broken, but the spool, spring, and housing cap still look sound. Rewind or install new line.
  • The spool is empty and your model uses a prewound replacement. Swap the spool rather than fighting a hand rewind.
  • The cap, eyelets, bump knob, or spring is cracked or missing. Line changes will keep failing until those parts are replaced.

This article walks through a safety-first sequence that covers those common Dewalt string-trimmer heads without treating any one design as universal.

Make the tool safe before you open the head

A spinning head can cut skin, throw broken line, and pinch fingers in the housing. Do not open the trimmer head while the tool can still start.

On a cordless Dewalt trimmer, remove the battery pack completely. Do not leave it seated and rely on the trigger lock alone. On a corded model, unplug the power cord from the outlet, not just from an extension cord that is still live at the other end. Keep your hand off the trigger while you handle the head. If the trimmer has a lock-off or lock-on control, leave it in the off position.

Wait until the head has fully stopped. Residual spin is short, but it is enough to slap line or a bump knob into your hand. Set the tool on a stable bench, step, or clean patch of ground so the shaft cannot roll and the head cannot drop. Support the shaft if the trimmer is top-heavy. Do not clamp the guard in a way that cracks it, and do not remove the debris shield to make the head easier to reach.

Wear eye protection. Cut monofilament line is stiff and can flick toward your face when you pull it from an eyelet or when you later test the head. Close-fitting gloves help with sharp housing edges, leftover line ends, and the spring that sits under some caps. Keep bystanders and pets away from the work area, including the brief no-load test at the end.

Do not defeat guards, tape down switches, or service a live tool. If the head is jammed so tightly that normal tabs will not release, stop and consult the model manual or a qualified repair shop rather than prying until plastic lugs break.

Identify your Dewalt head and choose compatible line

Look at the head you have before you buy or cut line. The answer is on the spool, the housing, and the owner’s manual, not in a single Dewalt-wide size.

How common head types differ

A bump-feed head usually has a rounded bump knob in the center of the housing cap. During cutting, a tap on the ground is meant to release a short length of stored line. An auto-feed head may look similar from the outside but is designed to advance line without that tap; the internal clutch or spring arrangement is different, so forcing a bump-feed rewind method onto it can leave the line trapped. A quick-load head is built so you pass a single length of line through the head or spool, center it, and wind both sides at once, often without fully dismantling every internal part. A fixed-line head uses short, separate pieces pushed into slots or holes; there is no long coil on a spool.

You can often tell dual-line from single-line by counting eyelets on opposite sides of the housing. Dual-line is common on many consumer trimmers because two cutting ends balance the head. Single-line heads exist as well. Do not assume yours is dual-line just because a neighbor’s Dewalt is.

Where to find line diameter and load method

Check three places, in this order:

  1. Molded text or icons on the spool and the inside of the housing cap. Many refillable heads show winding direction arrows and a listed line diameter.
  2. The rating plate or model number on the trimmer, then the matching section of the owner’s manual for that model.
  3. Any remaining factory line still on the spool. Matching that diameter is a practical starting point if the markings are worn, but the manual still governs if the two disagree.

Also note whether the head is meant for a prewound spool or a hand rewind. A prewound spool is a complete cartridge of line on a plastic core made for that head family. A reusable spool has slots, holes, or split compartments so you can anchor new line and wind it yourself.

What happens when the line does not match

Line that is much thicker than the head is designed for can jam in the eyelets, sit above the spool rim, or make the head hard to turn. That extra drag is a general strain on the motor and can leave the cap unable to close. Line that is much thinner breaks faster, slips in the winding slots, and may feed out in uneven bursts. Twisted, square, or other shaped line can work in some heads and bind in others; if the head or manual specifies round monofilament line, stay with that shape unless the documentation for your model says otherwise.

Uneven dual-line lengths make the head vibrate. Fused or heat-welded ends from a previous overload can act like a knot and stop feed even when the new line looks fine. There is no single factory length or diameter that fits every Dewalt weed eater, so treat every size claim you see online as model-specific until your head or manual confirms it.

Remove the old string or spool

Work slowly and keep the parts in order. Plastic lugs and small springs are easy to lose and easy to crack.

Open the housing cap

Look for arrows, tabs, or a press-and-twist pattern on the housing cap. Many bump-feed and auto-feed covers release when you squeeze opposite tabs or press the cap and rotate it in the direction of the arrows. Some caps unscrew. If the cover is only meant to twist, do not pry it with a screwdriver. A blade under a tab often snaps the lug, and then the cap will not stay closed later.

Lift the cap straight off once it is free. Set it inner-face up so you can see how the line path and any molded arrows were oriented.

Lift out the spring and spool

Some heads have a spring under the bump knob or under the spool. Note which end of the spring faced the spool and which end faced the cap. Photograph the stack or lay the parts out in the order they came off: cap, spring if present, spool, and any washers or retainers. Orientation matters. A spring installed upside down can keep the line from advancing or keep the cap from seating.

Slide the spool out of the housing. Watch how any remaining line still passes through the eyelets. That path is the same path the new ends must take. If leftover line is welded into a lump, cut it at the eyelets with scissors rather than yanking until the spool flanges bend.

Decide what to keep

Discard line that is short, brittle, flattened, fused, or badly curled. Brittle line snaps as soon as the head comes up to speed. If a reusable spool still has a useful amount of undamaged line and you only opened the head to inspect a jam, you can leave that line in place, clear the jam, and reassemble. If the line is a tangle, unwind it completely so the new wraps start clean.

Inspect the empty spool while it is in your hand. You want intact flanges, readable winding arrows, and undamaged anchor slots or through-holes. Inspect the eyelets in the housing. Grooves worn sharp will fray new line. Inspect the bump knob and cap for cracks. If those parts are failing, skip ahead to replacement rather than loading fresh line into a broken head.

Not every Dewalt cap opens the same way. If your head uses a different latch than a typical bump-feed cover, follow the graphics on that housing instead of forcing a twist that is not there.

Cut, insert, and wind the new line

The safest winding rule is simple: follow the arrows or winding graphics on the spool whenever they are present. Winding against those arrows is one of the most common reasons a freshly refilled Dewalt trimmer head will not feed.

Measure and cut without a printed length

If the manual or spool lists a cut length, use that length. If no printed length is available, cut enough monofilament line to fill the spool without stacking line above the rim. You want the wraps to sit in the grooves or between the flanges and still leave the cover free to close. Do not treat an internet measurement in feet or inches as a factory specification for every Dewalt model. It is better to cut a little long, wind until the spool is comfortably full, and trim the free ends after they pass through the eyelets.

Use scissors or line cutters. A ragged end is harder to feed through a small eyelet. If the line is coiled tightly from the package, let a working length relax so it does not spring off the spool while you wind.

Dual-line rewind on a reusable spool

Many dual-line spools are split into two compartments or have two anchor holes. The usual sequence looks like this:

  1. Fold or cut the line so you will load two roughly equal lengths, or use the spool’s center divider as the midpoint if the design calls for one piece shared by both sides.
  2. Anchor each end or the midpoint in the slot or hole provided. The line should click or seat, not sit on top of the flange.
  3. Wind each side in the direction of the arrows. Keep firm, even tension so the wraps lie flat and do not cross.
  4. Stop while the line is still below the rim. Overfilling prevents the housing cap from seating and can lock the spool so it cannot turn.
  5. Leave enough free end on each side to reach through the matching eyelet with a little extra to hold.

Keep the two sides from crossing. Crossed wraps bind when the head tries to pay out line. Equal lengths matter for balance; a long end on one side and a stub on the other will shake the shaft once the trimmer is running.

Through-the-spool and quick-load methods

On a through-hole or quick-load head, you typically feed a single length of line through the spool or through the assembled head until the midpoint is centered. Then you wind both sides together in the marked direction. The two ends stay opposite each other as they shorten. This method is faster when the head is designed for it, but it still depends on the same rules: correct direction, no crossed wraps, and no line piled above the rim.

If your Dewalt head is a true quick-load design, you may not need to remove every internal part. Align the eyelets with the through-path, push the line through until both sides are even, then twist the knob or spool as the head’s graphics show. If the line will not pass, stop and clear debris from the eyelets instead of forcing a thicker diameter through a blocked hole.

Prewound spools and fixed line

A prewound spool is already wound in the correct direction for that part. Transfer it into the housing in the same orientation as the old spool, with the free ends ready for the eyelets. Do not unwind a prewound spool “to check it” unless the wraps are obviously damaged.

Fixed-line heads do not use a stored coil. Cut short pieces to the length shown on that head or in the model manual, and push each piece fully into its slot or hole until it locks. Uneven stick-out on a fixed-line head causes the same vibration problem as uneven dual-line ends.

In every method, the line should sit neatly and stay below the spool rim so the cover can close freely. Do not expect a particular runtime or cutting performance from a given refill. Fresh line restores the cutting edge; it does not change the motor.

Reinstall the head and confirm the line feeds

Routing and reassembly are as important as the rewind. A perfect wrap will not feed if the ends miss the eyelets or the cap is only half latched.

Route the ends and seat the spool

Hold the free ends so they cannot spring off the spool. Place the spool back into the housing in the same orientation you noted when you removed it. Guide each end out through the correct eyelet. On a dual-line head, each end should exit the eyelet that matches its side of the spool. If an end is tucked under a wrap or trapped under the flange, it will not advance later.

Pull each end until it is snug against the winding, then leave a few inches outside the housing so you can see both sides clearly. Trim only after you know the cap will close. Wildly long ends can whip the guard; ends that are too short are hard to confirm during the first test.

Replace the spring and lock the housing cap

If the head uses a spring, put it back in its original orientation. The spring usually sits in a recess on the spool, the bump knob, or the cap. A tilted spring will make the cap rock or pop off.

Align the housing cap with the body. Press and twist, snap the tabs, or thread the cover the way it came off, until it is fully seated all the way around. A cap that is closed on one side and open on the other will vibrate loose. Check that the bump knob, if present, can move the small amount it is supposed to move and is not trapped by an overfilled spool.

Only after the head is closed should you reinstall the battery or plug the cord back in.

A low-risk feed check

Take the trimmer to a clear area away from people, glass, and loose gravel. Put on eye protection again. Start the tool for a brief no-load run and watch whether both sides of a dual-line head extend evenly and whether the head sounds smooth. You are checking assembly, not cutting brush.

If the head is a bump-feed design, a light tap of the bump knob on clean pavement or a wood block is a common way to see whether stored line advances. Keep bystanders away. Never tap against stone, metal, or concrete debris that can shatter line and throw fragments. Do not hammer the knob. If nothing comes out after a light tap, stop and reopen the head instead of hitting harder.

Not every Dewalt head is bump-feed. An auto-feed or quick-load head may advance line by design once it is running, or it may only need the ends to be pulled even by hand after winding. Use the check that matches the head you identified earlier.

Mistakes that cause jams, breakage, or vibration

Most refill problems come from the rewind, not from a failed motor. If the line will not advance after a refill, reopen the head and look for these errors first.

  • Wound against the arrows. The spool can turn, but the line binds in the eyelets or unwraps in the wrong direction. Rewind to match the molded graphics.
  • Crossed wraps. One loop climbing over another locks the coil. Unwind to the crossover and lay the line flat.
  • Overfilled spool. Line above the rim keeps the housing cap from seating and can clamp the spool so it cannot rotate.
  • Cover not fully latched. A half-closed cap shifts under load, pinches line, or flies off.
  • Mismatched line diameter. Oversized line jams in the eyelets or overloads the spinning head. Undersized line slips and breaks.
  • Unequal dual-line lengths. The head shakes, the shaft buzzes, and one eyelet may chew its line faster.
  • Fused or welded line. Heat from rubbing or from a previous stall can glue wraps together. Cut out the fused section and start clean wraps.
  • Debris in the eyelets. Packed grass can mimic a winding problem. Clear the holes before you assume the rewind is wrong.

New line that snaps immediately is often old brittle stock, line nicked by a worn eyelet, or line that was bent sharply against a flange. Vibration after the head is closed usually means unequal ends, a loose cap, a missing or tilted spring, or a spool that is not sitting flat in the housing. Forcing an oversized or jammed head to keep spinning is a general risk to the motor; stop and correct the jam rather than leaning on the trigger.

These are user-setup issues. They are not evidence of a specific Dewalt defect rate, and they do not require guessed temperature limits or melting points to understand.

When the problem is the head, not the string

Repeating line changes will not fix a worn housing. Stop and replace parts when you can see damage that keeps line from feeding or staying intact.

Worn eyelets develop sharp grooves. Fresh monofilament line frays or cuts through at those grooves within a short run. A cracked housing cap or a broken tab will not stay locked, no matter how carefully you wind. A flattened or missing spring on a bump-feed or auto-feed head can keep the spool from releasing line or keep the bump knob from working. A spool with a broken flange, stripped anchor slot, or worn-off winding arrows will not hold direction. A cracked bump knob can crumble the first time it taps the ground.

Do not ignore a cracked bump knob or a missing spring. Those parts are how some heads meter line. Running without them can dump the whole coil at once, or dump nothing at all.

Replacement heads and spools are model-specific. Match them to the model number on the trimmer, not to a look-alike head from another tool. A whole new cutting head is often the simpler fix when several parts are worn at once: eyelets, cap, and spool. Replacing the head restores a sound line path. It does not restore original power or battery life, and it will not correct a separate electrical or battery problem.

If the housing is shattered, the shaft is bent, or the head will not stay on the drive, that is beyond a string change. Use the model manual or a qualified service provider rather than improvising fasteners.

Troubleshooting after you change the string

If the first test does not go as planned, keep the checks mechanical and observational. Reopen the head only after you remove the battery or unplug the cord again.

Nothing feeds

Recheck winding direction against the arrows. Confirm each free end actually exits an eyelet and is not trapped under the spool flange. Confirm the spring is present and seated, if the head uses one. Confirm the housing cap is fully engaged all the way around. Clear packed grass from the eyelets and from the gap around the bump knob. If the spool was overfilled, remove a few wraps so the cover can close without clamping the coil.

Pull a short amount of line out by hand with the tool still de-energized. If it will not move by hand, it will not move in the yard. Find the bind before you run the motor.

Only one side of a dual-line head works

One end may have missed its eyelet, crossed into the other compartment, or broken inside the housing. Remove the spool and compare the two remaining lengths. Rewind so both sides are equal and each end has a clean path out. A blocked eyelet on one side only will also produce this symptom; inspect both holes.

The cap pops off during use

The cover was not fully latched, a tab is cracked, the spring is crooked, or the spool is too full to let the cap sit down. Inspect the lugs before you snap the same broken cap back on. A missing or damaged cap is not a “run it anyway” condition. Line and plastic fragments can leave the head.

The head is noisy or the trimmer shakes

Stop and de-energize the tool. Check for unequal line ends, a loose cap, debris stuck under the spool, or a spool that is not centered. Trim the two cutting ends to a similar length after a successful feed check if one side paid out farther than the other. Persistent vibration after those checks can mean a damaged spool or head, not a string problem.

The tool itself will not start

Treat that as a separate battery, latch, or electrical issue. Confirm the head is fully closed and the battery is seated only after reassembly, then follow the tool’s normal starting sequence. Do not diagnose control boards, invent error codes, or assume a warranty outcome from a line change. If a charged battery and a closed head still produce no response, the string is not the remaining problem.

A practical order of work

When you put the whole job together, the sequence stays the same even though Dewalt head designs differ:

  1. Remove the battery or unplug the cord. Wait for a full stop. Wear eye protection and gloves.
  2. Identify bump-feed, auto-feed, quick-load, or fixed-line hardware, and read the line-size markings on the spool, head, or manual.
  3. Open the housing cap the way its tabs or arrows intend. Set the cap, spring, and spool down in order.
  4. Discard spent or fused line. Keep only a sound reusable spool or install the correct prewound spool.
  5. Load new monofilament line in the marked winding direction, with equal dual-line lengths and no wraps above the rim.
  6. Route the ends through the eyelets, reseat the spring, and lock the housing cap completely.
  7. Restore power and do a brief, clear-area check that the line exits evenly. Use a light bump only if that head is designed to bump-feed.
  8. If feed, balance, or closure fails, de-energize the tool and correct winding, routing, or worn parts before you go back to cutting.

Changing Dewalt weed eater string is a short service procedure when the head is intact and the line matches that head. The details that matter are safety first, the correct load method for the head you actually have, and a rewind that follows the arrows instead of a generic video. When the markings on the tool and the model manual disagree with any outside tutorial, use the markings and the manual.