Greenworks 40V Trimmer Line Keeps Breaking — The Upgrade Path That Fixed It

A post in r/lawncare with 70+ comments started with a familiar frustration: “I have a basic Greenworks 40V 13” Cordless String Trimmer. No matter how careful I am trimming my lawn edges, the string breaks and every few minutes I need to open the casing and re-feed the string through the eyelet.”

The original poster eventually updated with the resolution — and it is worth reading because it applies to every budget battery trimmer on the market.

The original problem

The Greenworks 40V 13” (model 21332) ships with .065” round line. This is the thinnest standard trimmer line, and on a 40V motor with a 13” cutting swath, it is underpowered for anything beyond light grass. The moment you hit a sidewalk edge, a fence post, or any woody stem, .065” line snaps.

The owner’s edit, posted weeks later, tells the whole story:

“I sold the 40v and got a 60v greenworks trimmer, and strung it with .095 Trimmer Line. It is a beast and almost never breaks.”

Two changes solved the problem: more motor power (60V vs 40V) and thicker line (.095” vs .065”). But you do not necessarily need a new trimmer — fixing the line alone may be enough.

What the community recommended (ranked by upvotes)

1. Use thicker line — if your head supports it

u/44runner44 (r/lawncare moderator, 2024 Lawn of the Year winner) asked the key question: “What size line does that greenworks take? .095 is obviously going to be more durable than .065.”

The Greenworks 40V 13” head is rated for .065” only. This is the fundamental limitation — you cannot simply put .095” in a .065” head. The eyelet is too small and the motor may stall.

If your trimmer head only takes .065”, your options are:

Accept that .065” breaks on hard edges and trim more carefully
Replace the head with an aftermarket head that accepts .080” or .095” (see below)
Upgrade to a trimmer rated for thicker line

For trimmers that can run .080”, that is the sweet spot — see our .065 vs .080 vs .095 comparison.

2. Your line is dried out

u/Taossmith dropped the most upvoted single piece of advice in the thread:

“Store your string in a bucket or bag of water. It’s drying out and becoming brittle.”

u/-Skybopper- confirmed: “I had to replace a spool of line because it dried out and I couldn’t rehydrate it. It was breaking frequently.”

Nylon trimmer line absorbs moisture from the air, and that moisture is what keeps it flexible. Line stored in a hot, dry garage over winter loses its moisture and becomes brittle — it snaps on contact instead of flexing and cutting.

The fix: Before your next session, soak your spool in a bucket of warm water overnight. If the line is less than a year old, it will rehydrate and regain its flexibility. If it has been UV-exposed or stored for years, replace it.

3. Do not wind too tight

u/smokinbbq identified a winding technique issue: “If you wind it too tight, then it can’t flex and come out as needed, and ends up breaking inside. Since I’ve started relaxing the wind tension, I have had far fewer issues.”

Tight winding creates stress points where the line bends sharply around the spool. Under vibration and heat, these stress points fracture. Wind snugly but not stretch-tight — the line should have a slight give when you press on the wound coil.

4. Remove the guard and run longer line

u/Duty-Still offered the professional landscaper’s approach: “Get a Stihl. An fs91 will do. Remove the guard and run the string longer. At least .095” string.”

Running longer line (without the guard’s cutting blade trimming it short) gives each strand more flex before impact. More flex means more energy absorption, which means fewer breaks. The trade-off is a wider cutting swath that is harder to control for precise edging.

This is standard practice for commercial crews but may be too aggressive for a homeowner trimming along a driveway. If you try it, wear safety glasses — longer line throws more debris.

The upgrade path for Greenworks 40V owners

If you like your Greenworks 40V and do not want to buy a whole new trimmer, here is the most cost-effective upgrade:

Replace the stock head with an Echo Speed-Feed 400 ($22). It accepts .080” and .095” line and fits most trimmers with the included adapter bushings.
Use .080” twisted line instead of .065” round. Twisted line cuts better, resists breakage, and feeds more smoothly. See our twisted vs round comparison.
Buy bulk line instead of pre-wound spools. A 200ft roll of .080” twisted costs $12 and loads in seconds on a Speed-Feed head. That is enough for an entire season. See our cost comparison.