How do You Fix a Broken Lawn Mower String?

Fixing a broken lawn mower string usually takes less than 15 minutes and requires just a screwdriver and a new spool of trimmer line. The most common cause is simple wear from hitting hard surfaces, so you don’t need special skills to get your trimmer spinning again. Below you’ll find a complete guide that covers diagnosis, repair, and prevention of string breakage.

What Causes a Lawn Mower String to Break?

A lawn mower string, also called trimmer line or cutting line, breaks most often when it strikes concrete, rocks, or fences at high speed. Other common causes include:

Aged or brittle line – Trimmer line dries out and becomes brittle after a season or two in direct sunlight.
Wrong line diameter – Using line that is too thick for your spool or too thin can lead to frequent snapping.
Improper winding – If the line is wound unevenly or too tightly on the spool, it can jam and break inside the head.
Burrs or damage on the spool – Rough edges inside the trimmer head can fray and cut the line prematurely.

Understanding why the string broke helps you choose the right repair approach and avoid the same problem next time.

What Tools and Materials Do You Need?

Most repairs require no more than three items. Gather these before you start:

New trimmer line – Available in various diameters (usually 0.080 to 0.110 inches). Check your owner’s manual for the recommended size.
Screwdriver – Often a flathead or Phillips, depending on your trimmer head design.
Safety glasses – Broken line can snap and fly up during replacement.
A clean work surface – Avoid winding line over grass or dirt that can get inside the spool.

You may also want to keep a replacement spool on hand if your current one is cracked or worn. Consider a universal trimmer head replacement if you want to upgrade to a bump-feed or speed-feed model later.

Step-by-Step: How to Replace a Broken Trim Line

Follow these steps to fix your broken lawn mower string. The process is the same for most gas, electric, and battery-powered string trimmers.

Disconnect the power source – Remove the spark plug wire on gas trimmers, or unplug/take out the battery on electric models. Safety first.
Remove the trimmer head – Press the locking tabs (if present) or use a screwdriver to pry off the cover. Older models may have a screw in the center.
Take out the spool – Lift the spool out of the housing. Note which direction the line was wound (usually clockwise). Many spools have an arrow.
Clean the housing and spool – Use a rag to wipe away grass clippings, dirt, and oil. Inspect for cracks or burrs. A damaged spool can cause future breaks.
Cut a fresh piece of line – Measure a length of about 20 to 30 feet (6 to 9 meters), depending on your spool capacity. Most trimmer instructions suggest folding the line in half and winding from the middle.
Wind the line onto the spool – Insert the middle of the line into the slot on the spool. Wind tightly and evenly in the direction indicated. Keep tension so the coils lie flat. Stop when you have about 6 inches (15 cm) remaining on each end.
Secure the ends in the notches – Most spools have small slots or notches to hold the loose ends in place while you reassemble.
Feed the line through the eyelets – Place the spool back in the housing. Pass the two loose ends through the exit holes or eyelets in the trimmer head.
Replace the cover – Snap or screw the cover back on. Trim the ends to the recommended length (usually 4 to 6 inches beyond the edge of the head).
Test the feed – Gently tap the trimmer head on the ground to see if the line advances as it should. If not, the spool may be wound too tightly or in the wrong direction.

If you prefer a pre-wound spool to avoid winding, look for pre-wound trimmer spools that match your mower brand. They cost a little more but save time.

Why Does the String Keep Breaking After Replacement?

If you replace the string and it snaps again immediately, check these common issues:

Wrong line diameter – Using 0.095-inch line in a head designed for 0.080-inch line can cause jamming. The line snags on the housing edges and snaps.
Winding direction reversed – If you wound the line opposite the arrow, the spool will not release line properly, causing it to lock up and break.
Burred eyelets – The holes where the line exits the head can develop sharp edges from normal wear. Use a small file or sandpaper to smooth them.
Spool spring failure – A worn or missing spring inside the head can cause the line to feed unevenly. Replace the spring or the entire spool assembly.
Debris inside the head – Small stones or dried grass can block the line as it tries to feed. Clean thoroughly before rewinding.

When the problem persists after checking these, consider replacing the entire trimmer head assembly. A universal trimmer head with bump feed often solves issues with older heads that have worn parts.

How to Choose the Right String for Your Mower

Not all trimmer line is the same. Picking the right type prevents breakage and makes trimming easier. Here is a quick comparison:

Line Shape	Best For	Pros	Cons
Round	Light trimming (grass)	Smooth, quieter	Wears faster on hard surfaces
Square/Star	Heavy weeds, occasional edging	More cutting power	Can be noisier, wears spool eyelets faster
Serrated	Thick brush, tough vegetation	Aggressive cutting	Higher chance of breakage on impact
Twisted	General residential use	Strong, low breakage	Less common, pricier

Also note the line diameter. Most residential trimmers use 0.080 to 0.095 inches. Commercial trimmers often use 0.105 to 0.130 inches. Check your manual or the inside of your trimmer head for the "line gauge" marking.

For a reliable all-purpose line, many users prefer Oregon Magnum Gatorline for its durability and low shattering rate. It works well with gas and battery trimmers.

How to Prevent String Breakage in the Future

Taking a few simple steps can dramatically extend the life of your trimmer line.

Avoid hitting hard surfaces – When trimming near sidewalks, driveways, or fences, tilt the head so the line strikes the grass first, not the concrete. Let the line wear gradually rather than smashing it.
Store your trimmer indoors – Direct sunlight and extreme heat make the line brittle over time. Keep it in a garage or shed when not in use.
Trim at the right engine speed – Running the trimmer at full throttle all the time causes the line to wear faster. Use lower speed for light grass and save high speed for thick weeds.
Replace line regularly – Do not wait until the line snaps. Replace it when it gets shorter than 4 inches. Old line is more likely to break under load.
Keep the trimmer head clean – Remove debris after each use. Dirt buildup inside the head prevents the line from feeding and causes binding.

Seasonal maintenance tip: At the start of each season, inspect the entire trimmer head for cracks. Replace any worn parts before you begin trimming. This simple check prevents mid-season breakdowns.

What to Do When the String Won't Feed at All

Sometimes the string breaks but the trimmer refuses to release new line even after a proper rewinding. Try these fixes before giving up:

Check the bump feed mechanism – Most trimmers require a gentle tap on the ground to advance the line. If the mechanism is stuck, clean it with a small brush and lubricate with silicone spray.
Inspect the spring – A broken or weak spring will not push the spool down enough to release line. Replace the spring if it feels loose.
Look for a twisted spool – If the spool itself is warped from heat or damage, it can rub against the housing. Straighten or replace the spool.
Test the line length – If the line is too short (less than 3 inches sticking out), it may not catch the bump mechanism. Pull a few inches manually and tap again.

If none of these steps work, the entire trimmer head assembly may need replacement. Many hardware stores sell universal heads that fit multiple brands. Look for a string trimmer head replacement kit that includes the spool, spring, and cover.

Fixing a Broken Lawn Mower String Is Quick and Simple

A broken lawn mower string doesn’t mean your trimming session is over. With the right line and a few minutes of careful rewinding, you can be back at work quickly. The key is picking the correct line diameter, winding it evenly, and keeping your trimmer head clean. If the string keeps breaking despite proper winding, check for burrs, wrong line shape, or a worn spool. A little preventive maintenance goes a long way: store your trimmer out of the sun, avoid hard impacts, and replace the line before it gets too short. Following these steps will save you time and frustration every season.