Greg Asks:
“I recently got brave and bought a tool to adjust the truss rod on my Martins. Not sure I know what I’m doing. Have you published any information that might help me out?”
Hi Greg!
I haven’t specifically written a post on truss rod adjustment, which is ironic because it’s one of the top questions I get about guitar DIY. The reason I’ve avoided it is because it’s a tough topic to tackle in writing. Every guitar is just a little different in how it responds to tweaks, so there’s always a bit of “feel” and experience that comes into play.
However, there are some basic rules you can follow when adjusting your acoustic guitar’s truss rod. Here’s what I’ll cover:
- Which direction to turn your truss rod to tighten vs. loosen it
- The effects of tightening vs. loosening the truss rod
Which Direction to Turn the Truss Rod Bolt
When it comes to turning the truss rod bolt, just follow the old adage: righty-tighty (clockwise) and lefty-loosey (counter clockwise). That’s if you’re oriented so that you’re facing the truss rod bolt itself. Here’s what I mean:
If your truss rod is inside the soundhole (like most acoustics), you’d be standing at the body-end of the guitar (where the strap button is) staring straight down the guitar toward the headstock. That’s where it’s righty-tighty and lefty-loosey. I’ve shown this in the photo below.
From this position, it’s righty-tighty and lefty-loosey
On the other hand, if you’re doing this with the guitar in the playing position, you’ll push your truss rod wrench’s handle down toward your lap to tighten, or pull it up towards your face to loosen.
Do this in very small increments. No more than about 1/8th or 1/16th of a turn at a time.
In the playing position, it’s down to tighten and up to loosen
The Effects of Tightening or Loosening Your Truss Rod
The Effects of Tightening the Truss Rod
Tightening the truss rod will apply back-pressure to the neck, essentially bending it backwards and counteracting the the pull of the strings.
Tightening the truss rod will apply back-pressure to the neck, helping it counteract the pull of the strings
Why or When You Should Tighten the Truss Rod
You’ll usually tighten your truss rod if your action (string height) is feeling a little higher than you’d like. Your guitar’s neck may have developed just a bit too much forward-bow (relief), which can be the normal result of humidity and seasonal weather changes.
However, note that significantly lowering the action on your guitar requires more than just a truss rod tweak. To make a big change in your acoustic guitar’s string height, you’ll need a full setup, which involves adjusting the truss rod, sanding the bridge saddle, and sometimes deepening the string slots of the nut.
If you tighten the truss rod too much in an effort to get your strings as low as possible, you’ll create a back-bow, which will cause excessive fret buzz or notes that fully fret-out (don’t make any sound at all). You never want backbow in a guitar neck.
As a side note: most guitar manufacturers send out their guitars with the action purposely on the high side, so that the future owner can lower it to their personal taste. So, if you’ve ever ordered a high-end guitar and been surprised at how high the strings are, this is why. It’s rarely due to poor setup at the factory.
The Effects of Loosening the Truss Rod
Loosening the truss rod will relive back-pressure on the neck, essentially allowing the neck to bend forward. You’ll do this if your strings feel too low, which is usually accompanied by annoying fret buzz or notes that completely fret-out (are completely muted).
Loosening the truss rod bolt will allow the neck to bow forward (also called “relief”)
Why or When You Should Loosen the Truss Rod
You’ll usually loosen the truss rod if your strings feel too low… which is often accompanied by excessive string buzz or notes that completely fret-out.
This can happen with excessive humidity, which causes the fretboard wood to swell enough that it actually bows the neck backwards slightly (or makes it flatter than it should be).
Give the Neck 1-2 Days to Fully Settle After a Truss Rod Adjustment
It can take a day or two for the neck to fully “settle” into an adjustment. You’ll certainly see some neck movement immediately after making a truss rod adjustment, but wait overnight to see the full effect, as the wood continues to slowly bend into its final position.
Many inexperienced guitar DIY-ers aren’t aware of this and think they’ve got their truss rod dialed-in… only to discover the next day that their action has mysteriously become too high or too low.
You can really end up chasing your tail this way, so be patient and give the neck enough time to settle. You can still play your guitar during this time.
Well done. Very clear, concise and simple. Yours was the 5th article I had read, and the one that gave me the highest comfort level. Thanks!
IMPORTANT! Only turn 1/4 turn. Stop! Let the guitar sit for a couple of days and let the wood expand or contract at it’s own pace. Check the clearance. Make another adjustment, if necessary. Visit the Martin website for their instructions. NEVER force or over adjust a truss rod–in either direction–at one time. You risk breaking it. It’s normal to have to adjust the truss rod at least twice a year. Once for summer; once for winter. Also, if you travel to a different climate, some adjustment may be necessary. Knowing how to sight down the neck–or use a straight edge–and a feeler gauge to check relief, is the correct and most accurate way to set the neck with the truss rod adjustment.
Great info, simply and clearly presented. The illustrations are a great help. Thanks and merry Christmas a happy new Year !
Thanks John, glad you found the info helpful. Happy holidays to you as well!
Just a note, as I looked up how to adjust the truss rod, and did find this article helpful. (Sorry- not sure how to leave a general reply so tagging it on here…)
My Yamaha LL11 has the rod access in the headstock, so the directional advice you give for the access being through the sound hole is the opposite in this case. Probably other people would figure that out too, but, just to mention. Cheers
M
I agree, I need to make this explicitly clear (and now realize I didn’t).
We all know that tighty-righty and lefty-loosey stays the same, but that depends on your orientation to the bolt (head-on, facing the headstock vs. with the guitar in the playing position).
I don’t have an acoustic with a headstock-accessed truss rod, so perhaps I can just fudge it by using one of my electrics as an example.
So thanks so much! Very helpful in a detailed yet simplistic formula that highlights letting the neck tension after initial adjustment, is very vital! Peace in the Lord
Thanks a bunch.
I had tried to lower the action on my guitars by filing the nuts.
Some of my guitar had that truss rod built in. Compared to other articles about truss rod online, yours is the most clear.
Thanks for the feedback L. I’m glad you found the article useful.
To lower the action on an acoustic, you usually need to file the bridge saddle down, not the nut. However, a thorough setup does often involve filing the nut and saddle lower, as well as an adjustment to the truss rod. However, to get the most dramatic change in action, it’s the bridge saddle you want to lower. Only try to lower the action at the nut if you find that it feels too high down there in the first couple frets.
I find that about 0.4mm at the 7th fret is normally about enough curve in the neck. This is the distance between the top of the fret and a straight edge laid (with care!) on the fretboard. I’ve been setting up like this for about 30 years and in all that time only one guitar has seemed to work better with a perfectly straight neck – a Ferch ”Vintage one”. With electrics I’ve followed this advice – get the neck straight, and the string tension will pull the neck forward just enough. Seems to work for me.
Hi Richard. That sounds like a lot of relief, but doesn’t mean it’s “wrong.” Use whatever relief gives you the most comfortable action with the least buzz. Some necks do need a good amount of relief.
On my electrics I usually aim for .004″ – .006″ (depends on the particular guitar), and I measure the same way you do: with a straightedge laid along the frets and by sliding a .004″ feeler gauge between the to around the 7-9th frets. That’s pretty close to flat, but is what I’ve found works well on my electrics.