Bump feed trimmer heads use centrifugal force to advance new line as you tap the head on the ground
A bump feed head automatically feeds fresh trimmer line when you tap the bottom of the head against the ground while the trimmer is running. When the line wears down or breaks, you do not need to disassemble anything — you straightforward wind new line onto the spool inside the head, snap the spool back in place, and resume trimming. The whole job takes five to ten minutes and requires only the replacement line itself.
The process differs from fixed-line or semi-automatic heads because bump feed heads are designed for quick line replacement without tools. You are working with a spring-loaded spool that sits inside a plastic housing. Once you understand how the line winds onto that spool, the rest is straightforward.
Key Takeaways
- Bump feed heads have a removable spool inside a plastic cap; twist or pull the cap to access the spool.
- Wind new line into the two slots on the spool, leaving four to six inches free on each side, then snap the spool back into the housing.
- The line must wind in the direction the spool rotates — clockwise on most trimmers, but check your manual if you are unsure.
- If line does not feed after tapping, the spool may be wound too tightly or the line may be jammed in the housing.
Remove the bump feed cap and spool
Stop the trimmer and let it cool for a minute. Locate the plastic cap at the bottom of the trimmer head — this is the bump feed housing. On most models, you either twist the cap counterclockwise by hand or pull it straight down. Check your trimmer manual if you are unsure which motion your model uses; some caps are threaded, others are friction-fit.
Once the cap comes free, you will see the spool inside. The spool is a plastic wheel with two slots or notches around its edge — these are where the line winds. Lift the spool out of the housing. You may need to remove a small spring or washer underneath; set these aside in a safe place so you do not lose them.
Clean out old line fragments and debris
Before you wind new line, look inside the housing for bits of old line, grass, or dirt. Wipe the inside of the cap and the spool with a dry cloth. If debris is packed in the slots where the line feeds out, use a small brush or an old toothbrush to clear it. A clean housing helps the new line feed smoothly when you tap the head.
Pay special attention to the two small holes or slots on the outer edge of the housing — these are where the line exits. If they are clogged, the line will not advance properly even if the spool is wound correctly.
Wind new line onto the spool
Check your trimmer manual to confirm which direction the spool rotates. On most gas and electric trimmers, the spool turns clockwise when you look at it from below. Wind the new line in that same direction. If you wind against the rotation, the line will not feed.
Insert one end of the line into one of the two slots on the spool. Wind the line around the spool in the correct direction, keeping it tight and even. When you reach the other slot, insert the line end into it and continue winding until the spool is full. Leave four to six inches of line free on each side — this is the cutting length that will stick out of the head.
Do not wind the line too tightly. If the spool is packed so full that it cannot turn freely inside the housing, the line will not feed when you tap. A moderately firm wind is correct — the spool should spin easily by hand when you hold it.
Reinstall the spool and cap
Place the spool back into the housing, making sure the line ends are still in their slots. If there was a spring or washer under the spool, put it back in place first. The spring helps the spool advance the line, so do not skip this step.
Snap or twist the cap back onto the housing. If your cap is threaded, turn it clockwise until it is snug — do not force it. If it is friction-fit, push it down until you hear or feel it click into place. The cap should sit flush with the head.
Test the line feed
Start the trimmer and let it run at idle speed. Tap the bottom of the head gently against the ground. You should see the line advance slightly. If nothing happens, stop the trimmer and check that the line is seated properly in both slots. If the line is jammed or the spool is wound too tightly, remove the cap and adjust.
Once the line feeds, trim a small patch of grass to test the cutting length. If the line is too long, it will slow the trimmer or cause vibration. If it is too short, tap the head again to advance more line. Most bump feed heads will advance a small amount with each tap, so you can dial in the length you want.
Troubleshoot if the line does not feed
If you tap the head and nothing happens, the spool may be wound too tightly. Remove the cap, take out the spool, and rewind it with slightly less tension. The spool should turn freely when you spin it by hand.
If the line is jammed in the housing, remove the cap and gently pull the line free. Make sure both line ends are fully seated in their slots before you reinstall the spool. Sometimes a small piece of old line gets caught in the exit holes — if that is the case, clear it with a thin tool or a straightened paperclip.
If the line still will not feed after these steps, the spring under the spool may be damaged or missing. Check your manual for the correct spring part number and order a replacement. A broken spring prevents the centrifugal force from working, so the line will not advance no matter how hard you tap.
Frequently Asked Questions
How much line should I leave sticking out of the head?
Leave four to six inches on each side. This is the cutting length. If you leave more, the line will be too long and will slow the trimmer. If you leave less, you will need to tap the head more often to advance fresh line.
What if I wind the line in the wrong direction?
The line will not feed when you tap. Remove the cap, take out the spool, and rewind the line in the opposite direction. Check your manual to confirm which way the spool rotates on your model.
Can I use any brand of trimmer line?
Most bump feed heads accept standard .080-inch or .095-inch line, but check your manual for the correct diameter. Using the wrong size can cause feeding problems or poor cutting. The line type — round, twisted, or serrated — is usually a matter of preference, but round line is most common.
How often do I need to replace the line?
It depends on how much you trim and what you are cutting. Dense weeds and thick grass wear line faster than light lawn trimming. You will know it is time when the line becomes noticeably shorter or breaks during use. Most people refill the spool every few weeks during the growing season.
Do I need to replace the whole head or just the line?
Just the line. The spool and housing last for years if you keep them clean. Replace the entire head only if the cap cracks, the spool breaks, or the spring wears out — which is rare.