What do I need to adjust acoustic truss rod?

My acoustic truss rod is adjusted here. I just tried my Allen key in it and I’m not sure it fitted , couldn’t get leverage to tighten it to correct high action / bow

Please can anyone recommend a specific tool I need ?

That looks like it should be a typical Allen wrench. You may need the right size for the guitar and they are definitely fiddly.
If it feels like it fits but you can’t turn it easily, take it to a tech, you would hate to break it.

1 Like

Why exactly do you want to adjust the truss rod?


Did your guitar not come with the appropriate tool to adjust the truss rod, Lewis. I suppose not or you’d not be asking. Perhaps you can confirm some specs on the internet and be certain exactly what you need.

@Malz Mal, the truss rod supports the neck of the guitar which is under tension from the strings. You can add more or less counter-tension via the truss rod which influences the curve of the neck. The neck is usually a little concave. This influences the guitar action (height of strings above the neck). It is referred to as neck relief and getting that right is part of a guitar setup.

1 Like

Hi Malz,

I’ve had the guitar for around ten years and never adjusted anything. The action of the strings is now really quite high as they get toward the bridge .

I also had trouble adjusting the truss rod on my acoustic some time ago. Just like you, it felt like the allen key was engaged, but I couldn’t get anything to turn. Turned out that the bottom of the truss rod was actually a lot deeper than the hole suggested, and that the channel leading to it narrowed as it got deeper, so the allen key had just jammed into the wood.

That’s a very long-winded way of saying, try a smaller allen key! Also, remember not to force anything. If it really won’t budge with a little effort, take it to an expert.

1 Like

The 1st Allen wrench is a standard 5 mm that had worked with the acoustic and electric guitars I’ve owned over the years. Can be bought at any hardware store. Limited leverage when dealing with sticky truss rods. But should work for you…with care.

The 2nd one is what I had to buy for my Martin. Has good leverage, and a ball tip, which is really nice. Green painter’s tape protects the strings. About $15 CDN from Amazon, IIRC.

(Tape measure in inches)

Note that it takes quite a bit of force to tighten an acoustic truss rod. Perhaps especially so in your case where it has never been adjusted.

There are probably some good YouTube videos on how to do it, if you don’t know anyone who can show you.

1 Like

This is not a good reason to adjust the Truss Rod. The Truss Rod will give you a few mils at most around the 7th fret. If the action on your guitar is high at the 12 fret the truss rod will do nothing to fix that. you need your guitar set up properly not a truss rod adjustment

Do you properly humidify your guitar? It could be drying out.

So, I have said this in several threads.

Truss rods adjust relief. They DO NOT adjust action. Always adjust the truss rod BEFORE adjusting action.

Relief changes with string tension changes and can be checked by fretting the 6th string at the 1st and 12th fret. There should be about a business card thickness gap under the string at the 6th fret.

If it is less or touching, you have back bow and buzz. Adjust by loosening the truss rod enough to barely slide that card under.

If it is greater, yes, you have higher action and some additional difficulty playing. Adjust by tightening the truss rod until the card barely slides under. IF AND ONLY IF this is the case, will a truss rod adjustment just by happenstance reduce action, but it is not how you reduce action.

Action increases over time with the constant pull of the strings on the neck. It is adjusted (after the truss is adjusted) at the saddle primary and occasionally the nut. Worn frets or frets that are really low from being redressed a bunch can also affect action.

Generally if the action is high, you usually trim the saddle down. After making sure the nut is ok, of course (and the truss rod!)

If the saddle is too low to trim, you need a neck reset.

If you are uncomfortable about any of this and are planning to adjust the truss rod without really knowing what you are doing, you are unlikely to improve your guitars play.

For relatively little money, a guitar tech or luthier can do it all correctly.

I hope that helps!


I don’t think I’ve ever adjusted a truss rod that turned “easily”…they’ve always felt sticky at first…kind of like a stubborn lid on a jar.

David, thanks for the info.

I suspect that the OP was a little fuzzy on the distinction between relief and action, like I was until you corrected me a few days ago (appreciate the clear definitions, BTW).

However, to further improve my own understanding…

Too much relief will also raise the action, correct?

Here’s a great video that uses an “acoustic guitar simulator” to visually explain how the various components of the guitar interact to produce the overall action.

Yes, but not exactly the way you would want to. Since increasing the relief actual curves the fretboard, it won’t linearly increase relief along the length of it.

1 Like

The bottom gibson video has the acoustic towards the end of the video

Cheers , yeah Action is really high at 12th fret. I can still play the guitar fine but I have another acoustic with nice action and want it to be more like that one.

Maybe I’ll take it for a setup if the truss rod isn’t going to make any difference

1 Like

Truss rod might make a difference.

I have an older Yamaha that I tried to turn the truss rod and just couldn’t. Pulled on it pretty hard too. Decided not to force it so left it.

My good acoustic needs a special tool. But comes with free adjustments for life at the music shop I bought it from. When action was all wacked out, because of humidity, and also the fact it was a new guitar and needed to adjust to the climate, they adjusted the truss rod and made it perfect again. Quite low action and great playability.

1 Like

Be careful and take your time . What I do I make small changes and wait one day for it to settle down. Also make sure you have the right humidity . Just take your time and let the guitar is settled :slight_smile: