A tangled spool or debris buildup is the primary reason for a black and decker trimmer auto feed not working, which happens in most cases when the line can’t advance freely. You can confirm this by checking the spool area for grass or dirt preventing the line from releasing.
Why your Black and Decker trimmer auto feed not working
| Cause | How common | How to confirm it | Fix it yourself? |
|---|---|---|---|
| Tangled line | Very common | Pull line manually | Yes |
| Debris buildup | Common | Inspect spool head | Yes |
| Empty spool | Common | Check line level | Yes |
| Incorrect winding | Occasional | View spool pattern | Yes |
| Worn feed spring | Rare | Check spring tension | Yes with care |
| Damaged spool cap | Rare | Check for cracks | Yes |
| Motor failure | Very rare | Listen for noise | No |
Tangled line inside the spool
The most frequent cause is line overlapping inside the spool, which prevents the centrifugal force from pulling new string out during use. This usually happens when the trimmer is stored or used at an angle, causing the line to cross over itself. To confirm this, remove the spool cover and manually pull the line; if it resists or feels stuck, it’s tangled. Unwind the entire length of the line, inspect it for kinks or melted spots, and wind it back neatly according to the arrows printed on the spool. This takes about 10 minutes. If the line is damaged, replace it with the official line replacement guide provided by the manufacturer.
Debris blocking the feed mechanism
Dirt, small rocks, and dried grass often get trapped between the spool and the cap, physically locking the feed mechanism in place. If you notice the trimmer head doesn’t move or feels stiff when you tap it against the ground, debris is the likely culprit. To check, remove the cap and look for packed organic matter or stones blocking the path of the line. Clear away all residue with a soft brush or a dry cloth. Don’t use metal tools to scrape the plastic, as this can create rough edges that catch the line later. This fix usually takes 5 minutes. If you see deep gouges in the plastic, the cap may need a replacement part.
Running out of trimmer line
The auto feed system can’t function if there’s no line left on the spool to release. This is often overlooked because the line can become very short before the user notices. To confirm this, look at the spool through the clear window on the cap or remove the cap to see the remaining length. If you see only a few inches of line, you have reached the limit of the spool capacity. Replace the spool with a new one that matches your specific model number, as using the wrong size can cause the feed to fail immediately. This takes 2 minutes and requires no special tools beyond the new spool assembly.
The less likely causes
- Incorrect winding: The line must be wound in the exact direction indicated by the arrows on the spool, or it will bind against the housing.
- Worn feed spring: If the spring inside the spool head has lost its tension or is missing, it can’t push the spool back to release the line.
- Damaged spool cap: A cracked or deformed cap won’t sit flush on the housing, which prevents the bump-feed mechanism from activating correctly.
- Motor failure: If the trimmer head doesn’t spin at all, the issue is electrical; this requires a qualified service center, as internal repairs carry a risk of shock.
What a fix usually involves
Most repairs involve simple cleaning or replacing a small part like the spool or the plastic cap. These components are inexpensive relative to the price of a new unit. If the problem is the motor, it’s often more cost-effective to replace the entire trimmer than to pay for professional labor. You can find specific part numbers in your owner’s manual or on the manufacturer’s website. Always use genuine parts to ensure the feed mechanism operates at the correct speed and tension for your specific model.
Frequently asked questions
Can I use any type of string for my trimmer?
No, you must use the specific diameter and shape of line recommended for your model. Using the wrong size will prevent the auto feed from working because the line will be too thick to slide or too thin to hold tension.
Is it safe to fix a trimmer while it’s plugged in?
No, you must disconnect the power cord or remove the battery before inspecting the spool. Working on a powered tool creates a risk of accidental startup, which could cause serious injury to your hands.
How long should the trimmer line be?
It should be long enough to reach the guard but not so long that it drags on the ground. Check your manual for the exact length, as this varies by model — check the label on the trimmer shaft.
What happens if I force the line out?
Forcing the line out can damage the plastic tabs on the cap or the spring mechanism inside the head. This usually results in the cap falling off during use and requires you to buy a replacement part.
Does it matter if I wind the line by hand?
Yes, you must wind the line tightly and in even rows to prevent tangles. If you wind it loosely or cross the lines, the centrifugal force won’t be strong enough to release the line during operation.
Why is my trimmer making a loud grinding noise?
This noise usually means debris is stuck inside the head or the spool isn’t sitting correctly. Stop the tool immediately, remove the power source, and inspect the head for stones or broken plastic parts.
Final Thoughts
If you still can’t get the line to advance after cleaning the spool, it’s likely time to replace the entire spool assembly. You’ll find that fresh, pre-wound spools often solve these persistent issues instantly. Don’t hesitate to reach out to the manufacturer if you’re still having trouble with your equipment.
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Dorothy Addeo is a senior product reviewer at Safefins.com with years of experience testing kitchen, furniture, backpacks, and everyday lifestyle products. She focuses on comfort, durability, usability, and long-term value through hands-on research and real-world testing. Her goal is to help readers find reliable products with honest, easy-to-understand recommendations they can trust.