“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?”
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.
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.
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.
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).
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.