How to Restring a Kobalt 40V Trimmer

To restring a Kobalt 40V trimmer, remove the battery, reload the head with compatible nylon trimmer line in the marked winding direction, and secure the head before testing it. The loading method depends on the installed head: a removable spool is wound by hand, while a quick-load head accepts line through its eyelets. Identify the head first so you don’t open parts unnecessarily or wind the line backward.

Identify Your Kobalt Trimmer Head

The restringing method follows the installed head, not the battery voltage.

Look for the model number on the trimmer’s identification label. These spool-cover instructions identify the KST 2540-06.

If the original head has been replaced, its own loading instructions take precedence over those for the original head.

Use the head’s features to choose the appropriate method:

What You Find	Loading Method
A removable spool with line anchors and winding arrows	Open the cover, remove the spool, and wind it by hand.
A head identified as quick-load, with alignment marks and a line-winding knob	Thread line through the assembled head and turn the knob.
A compatible prewound replacement spool	Exchange the spool rather than winding loose line.

A tabbed cover alone does not identify the loading method. Some quick-load heads also have removable covers for clearing jams or replacing internal parts.

How to Restring a Removable-Spool Kobalt Trimmer

Reloading a removable-spool head involves opening the cover, removing the spool, and winding new line in the marked direction. Have replacement nylon trimmer line, scissors, and a clean place to set down the spool and cover.

Step 1: Remove the Battery and Match the Line

Release the trigger and let the head stop completely.
Remove the battery pack before changing the line, cleaning the head, or opening the spool area.
Match the replacement line to the diameter specified for the installed head.

“40V” identifies the battery system, not the line diameter or spool capacity. Match the replacement line to the size and diameter of the line currently on your head.

Use nylon trimmer line, not wire or other substitutes. If you cannot establish the correct loose-line specification, a replacement spool explicitly listed for your model avoids guessing.

Step 2: Release the Spool Cover

Support the trimmer securely with the head accessible.
On the KST 2540-06, turn the trimmer over and press the two release tabs on opposite sides of the spool cover.
Lift the cover away while keeping control of the spool and any loose internal parts.

Press the actual flexible tabs, not another pair of points around the housing. If the cover does not release, check that both tabs are depressed before applying more pressure. Avoid prying against the plastic rim.

Step 3: Remove the Spool and Old Line

Note how the spool sits in the housing and how the line passes through the eyelets. A photo can help preserve the arrangement.
Lift out the spool, keeping any spring or separate bump-knob components in their original order.
Remove the remaining line.
Brush away grass and loose debris from the spool, housing, and eyelets.

Inspect the parts before reloading. A cracked spool, damaged eyelet, or broken cover latch needs attention; new line will not correct a mechanical fault.

Step 4: Anchor and Wind the New Line

Prepare the loading length specified for the installed spool.
Find the spool’s line anchor and winding arrow.
Secure the line using the anchor arrangement the spool provides.
Wind in the arrow’s direction, keeping the line snug and evenly distributed.
Leave the working ends free and place them in the temporary retaining notches, if fitted.

Spool layouts differ. A divided spool may hold separate line sections in separate channels, while another design may anchor the midpoint of a continuous piece. Use the arrangement built into the spool rather than copying a different head’s threading pattern.

Keep each line section in its intended channel. Avoid loose loops, diagonal crossings, and line trapped beneath earlier wraps. Respect any molded fill limit; the finished winding should remain below the spool rim rather than bulging beyond it.

Wind the line in the direction specified for the installed spool.

Step 5: Reinstall the Spool and Cover

Place any spring or separate internal component back in its original position.
Guide the line ends through the housing eyelets.
Seat the spool fully.
Release the ends from their temporary retaining notches, if used.
Fit the cover and make sure every latch engages.

Check that no line is pinched between the cover and housing. The cover should sit evenly, without a lifted edge.

Leave enough working line to reach the guard’s cutoff blade, but trim away excessive loose tails before starting the tool. The cutoff blade controls the working length; it is not a reason to start the trimmer with a large loop hanging from the head.

Step 6: Test the Reloaded Trimmer

Confirm that the guard, spool, and cover are securely installed.
Move to a clear outdoor working area and put on eye protection.
Reinstall the battery and run a controlled test, keeping the head away from people and objects.
Check that the head runs smoothly and the line advances using its intended feed mechanism.

For a bump-feed head, test line advance with a controlled tap of the bump knob against the ground during normal trimming. Do not repeatedly strike the head if it fails to feed.

Stop and remove the battery before investigating unusual vibration, a loose cover, or a feeding problem.

Quick-Load and Prewound-Spool Options

Quick-load heads and prewound replacement spools can eliminate hand winding, but the head or spool must match the trimmer.

Reloading a Quick-Load Head

Use this method only when the installed head is designed for through-head loading.

Remove the battery and clear out any remaining line that obstructs the loading passage.
Prepare the correct line type and loading length for that head.
Turn the winding knob to align the head’s loading marks.
Feed the line through the designated opening and out the opposite eyelet. For a head that loads a continuous piece this way, center it so the exposed ends are equal.
Turn the knob in the indicated loading direction, keeping the line from looping or tangling outside the head.
Stop with usable tails extending from the eyelets. Trim excessive slack and confirm that the cover and guard are secure.
Reinstall the battery and test the trimmer in a clear area while wearing eye protection. Stop and remove the battery if the head vibrates abnormally or the line will not advance.

If the line will not pass through, verify the alignment before pushing harder. A blocked passage may contain a short piece of old line.

Installing a Prewound Spool

Choose a prewound spool listed for the trimmer’s full model number; if the head has been replaced, match the spool to the installed head.

Remove the battery.
Release the cover using that head’s latch arrangement and lift out the empty spool.
Retain any spring or separate component that is not included with the replacement.
Thread the replacement spool’s working ends through the housing eyelets and seat the spool.
Release the line from any temporary shipping or retaining notches, then latch the cover completely.
Check that the line is not pinched and that the guard is secure.
Reinstall the battery and perform a controlled outdoor test with eye protection. Stop and remove the battery if the cover shifts, the head vibrates, or the line fails to feed.

Do not force an almost-fitting spool into the housing. Its diameter, height, drive features, and feed mechanism must all match.

Why New Trimmer Line Won’t Feed

A common experience during reloading is resistance at the line-winding knob. Resistance alone does not identify the cause, so inspect the loading arrangement rather than assuming the knob has failed.

Symptom	Likely Cause	What to Correct
Line will not advance	An end remains in a retaining notch, wraps cross, or line is pinched	Release the trapped end and inspect the winding and eyelet path.
Line unwinds while you reinstall the spool	The ends are unsecured or the wraps are loose	Rewind snugly and use the spool’s retaining notches where provided.
The winding knob becomes hard to turn	Excess line, tangled wraps, debris, or misaligned loading parts	Clear debris and verify the loading path and spool capacity.
The cover will not close	The spool is not seated, a component is misplaced, or line lies across the rim	Restore the internal arrangement and clear the cover’s seating surface.
Only one line end feeds	A wrap or eyelet on that side is obstructed	Inspect that line channel and remove the obstruction.
The head vibrates after reloading	Uneven working ends, an incorrectly seated spool, or damaged parts	Correct the seating and line arrangement; replace damaged parts before use.

Start with visible obstructions and seating problems before taking apart additional components. If the spool is tightly packed or crossed, removing the line and rewinding it neatly is more useful than repeatedly bumping the head.

After a correction, reseat the spool, route the ends through the eyelets, and latch the cover completely. Confirm that the guard is secure, then reinstall the battery and test in a clear area with eye protection.

Confirm the Reload and Prevent Another Jam

A successful reload gives you smooth rotation and predictable line advance. A bump-feed head normally holds its line while at rest, so an end that resists a simple hand pull is not automatically jammed.

During the first trimming pass, watch for these signs:

The head runs without unusual vibration or rattling.
The line remains captured rather than spilling from the spool.
The feed mechanism releases line when operated normally.
The cover stays seated.

To reduce future jams, keep the spool channels and eyelets free of packed grass, use the specified line, and avoid overfilling the spool. Let the line tips cut rather than pressing the head into fences or other hard surfaces.

Once the trimmer passes its feeding and vibration checks, resume trimming.

Frequently Asked Questions

How Do I Restring an Older Kobalt 40V Max Trimmer?

For an older Kobalt 40V Max trimmer, the installed head—not the battery voltage—determines the loading method. Find the model number on the trimmer label and identify whether the head uses a hand-wound spool, through-head loading, or a replaceable prewound spool. If a replacement head has been fitted, use that head’s line specification and loading arrangement.

Do I Need to Remove the Entire Head to Change the String?

Usually not: routine restringing involves loading through the head or removing its cover and spool, not detaching the complete assembly from the drive shaft. Complete head removal is a separate procedure with model-specific fasteners and thread directions. Remove the battery before either job, and do not assume that twisting the entire head will release the spool cover.

What Replacement Parts Might I Need for a Kobalt Trimmer Head?

Depending on the fault, the needed part may be the spool, spool cover, bump knob, spring, housing, or complete head assembly. Availability and compatibility vary by model, and a worn bump knob does not necessarily require replacing the whole head. Match the part listing to the trimmer’s full model number, and to the installed head if it is no longer the original one.