Truss Rod Adjustment Acoustic: How to Do an Acoustic Guitar Truss Rod Adjustment

Published Categorized as Guitar Care Tuning Restringing, Setup

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acoustic guitar truss rod adjustment

You might need to do an acoustic guitar truss rod adjustment for a couple of reasons.

It might be because you need to adjust the action of your guitar. Whilst the truss rod adjustment itself isn’t necessarily going to set the action how you want it, it is a necessary first step. You will want to make sure your guitar neck is set how it should be before you start adjusting the nut on a guitar, or adjusting the saddle.

It might also just be because guitar’s neck has warped and either adopted too much relief or it has back bow.

  • Relief = the middle of the fingerboard is dipped in, so that the gap between the strings and the fingerboard is higher in the middle frets than at the nut end and the body end of the fingerboard.
  • Back bow = the middle of the finger board is raised – the strings are closer to the fingerboard at the middle frets than at the nut end and body end of the fingerboard.

Table of Contents

Types of Truss Rods

There are two main types of truss rods used in acoustic guitars – single-action and dual-action. Single-action truss rods can only be tightened, while dual-action truss rods can be both tightened and loosened. Dual-action truss rods have an adjustment nut at both the headstock and body ends, allowing more versatility in truss rod adjustments. Most modern steel-string acoustics have dual-action truss rods. Let’s have a deeper look at each type.

Single Action Truss Rod

A single-action truss rod can only be tightened, not loosened. This type of truss rod is designed to counteract the tension created by the strings which causes the neck to bend forward over time.

How It Works

  • The single-action mechanism allows the rod to be tightened in one direction only, creating outward pressure to offset string tension.
  • Turning the truss rod adjustment nut clockwise increases tension on the truss rod, flattening the number of forward bows in the neck.
  • The adjustment range is limited since the truss rod can’t be loosened, only tightened within its built-in tension range.

Application

  • Ideal for rigid neck guitars that require limited truss rod adjustment.
  • Allows control of neck relief to compensate for string tension over time.
  • Not suitable if significant adjustment in both directions is needed to control neck bow and relief.
  • Provides a cost-effective truss rod solution for many mass-produced acoustic guitars.

While single-action truss rods offer simplified tension adjustment in one direction, the limited range and inability to loosen the rod makes dual-action truss rods more versatile for most applications.

Dual Action Truss Rod

A dual-action truss rod allows adjustment in both directions to control the amount of neck bow and relief. This type of rod offers more versatility compared to a single-action truss rod.

How It Works

  • A dual-action truss rod has an adjustable nut at both the headstock and body ends of the neck.
  • Turning in one direction increases rod tension, flattening any forward bow.
  • Turning the opposite way loosens tension, allowing some upward bow if needed.
  • This bi-directional adjustability allows control of both the back bow and forward bow as needed over time.

Benefits

  • Allows neck relief to be set and adjusted as needed in both directions within the rod’s tension range.
  • Compensates for string tension changes over the lifetime of the guitar.
  • Accommodates adjustment for seasonal humidity changes.
  • Ideal for bolt-on neck guitars where the neck angle and bow may need adjustment.
  • Gives luthiers and guitar techs more precise control when doing neck adjustments.

The added flexibility of bi-directional truss rod adjustment makes dual action rods well-suited for most steel string acoustic guitars. Their capability to control both back bow and forward bow as needed provides versatility lacking in single action rods.

How often should I need to adjust my Trust Rod?

Adjusting the truss rod is not a regular maintenance task. It should only be done when it is needed.

It may be the case that you need to do it once or twice a year (particularly in environments where the humidity changes drastically between seasons) or it may be the case that you don’t need to do it for 10-15 years.

This will depend on a couple of things:

  • The environment your guitar lives in; and
  • The guitar itself – particularly the neck of the acoustic guitar – i.e. how strong the neck is, what material it is made of, the tension of the strings etc.

How to tell if I need to do an Acoustic Guitar Truss Rod Adjustment

Press on the first fret of the guitar and on the 14th fret (or whichever fret is the closest to the body of the guitar – usually the 14th fret). This is most easily done by using capos – or at least a capo at one end to free up your hands.

Now measure the gap between the string and the fret at the 7th fret. You can do this using feeler string gauges or just lightly pressing on the string at the 7th fret to get a feel for the gap.

Now check the gap at the frets closest to the first fret and the frets closest to the 14th fret.

  • If the gap is the same at the 7th fret as it is towards the 1st fret and towards the 14th fret then the neck is straight. The gap is likely to be very slight in this case.
  • If the gap at the 7th fret is larger than the gaps towards the 1st and 14th frets then there is some relief in the neck. Relief simply means that the neck is slightly lower on the fingerboard in the middle frets.
  • If the gap at the 7th fret is less than the gaps at the 1st and 14th fret then there is back bow which means the fingerboard is higher in the middle than it is at the body and headstock ends.

Straight is not necessarily the best. Most guitarists like some relief in the neck. If you are looking for a standard the relief is most often set so that the gap at the 7th fret is .007″ (0.18mm) when the strings are compressed at the 1st and 14th frets. So it’s only very very subtle.

How To Choose A Truss Rod

When selecting a truss rod for your acoustic guitar, consider these key factors:

  • Desired adjustment range – If you only need to tighten the truss rod to add neck stiffness, a single-action rod will suffice. But for two-way relief control, choose a dual-action rod.
  • Guitar construction – Solid wood guitars are more prone to bowing issues from humidity changes than laminated models. Opt for the extra flexibility of a dual-action rod for solid wood acoustics.
  • Neck joint – Acoustics with bolt-on necks allow easier truss rod access versus set neck models. This makes periodic adjustments simpler if you get a dual-action rod.
  • Budget – Single-action rods cost less than dual-action variants. But the versatility of a dual-action may justify the extra expense, especially for higher-end models.

When deciding between rod types for your acoustic, weigh the pros and cons:

  • Single-action rods only allow tightening but provide an affordable option.
  • Dual-action rods enable two-way adjustment but add cost due to more complex installation.

Tools Required for Truss Rod Adjustment

You just need a few key items on hand:

  • Allen wrench – The properly sized wrench to fit your truss rod nut. Metric sizes around 3-5mm are typical.
  • Feeler gauges – Thin metal strips used to accurately measure string/fret gap when checking neck relief. Lower than .002″ may be required.
  • Capo – Useful for holding down strings, allowing easier access when doing measurements.
  • Tuner – Clip-on or app to ensure strings stay tuned to proper pitch before/after adjustments.

Small Adjustments

Because the truss rod can have a delayed reaction it’s important to only adjust it a small amount at a time. I’d even go as far as making a small adjustment one day and then re-checking the next day and making another small adjustment if necessary and so on until it is right.

But, the truss rod adjustment isn’t a cure for action in itself. To lower action on acoustic guitar, you will have to do something else. However, I think it’s something that should be right before you adjust your action (at the nut and the saddle) because it will have an effect on the action.

Get the neck where it should be and then adjust the action at the nut and the saddle.

Accessing the Truss Rod

The access for adjusting the truss rod on an acoustic guitar is normally found either:

  • At the soundhole; or
  • Under a truss rod cover at the headstock end (usually you can get in there via a few screws)
accessing the truss rod
headstock access to the truss rod

The adjustment of the truss rods is usually done with an allen key or a socket wrench.

Adjusting the Truss Road

Like I have mentioned this is fairly involved and can have some critical outcomes if you don’t get it right.

It’s always a good idea to watch some guide that shows how to adjust acoustic guitar truss rod, before you do it on your own for the first time.

Only ever make small adjustments at a time and then re-measure. And always re-tune after making an adjustment so that the strings are at the right tension. Let it sit for a while before re-checking the measurement to give the guitar a chance to settle into its new shape.

Even go as far as to leave it for a day and re-measure the next day. If it still needs more adjustment then make another very small adjustment. Be patient – you don’t want to mess with your neck too much – and you definitely don’t want to snap the truss rod – this can be an expensive repair!

If the truss rod feels really tight don’t force it – if in doubt have a professional look at it for you.

But if it’s all looking good and your feeling confident to do it yourself then read on.

Here are the steps

  1. Remove the cover on the headstock (if your access is via the headstock)
  2. Make sure your guitar is in tune (to pitch). Unless you have perfect pitch use a tuner to make sure that it’s at the right tension – don’t just tune it to itself!
  3. Depending on whether you need to increase or decrease the relief will determine whether you need to loosen or tighten the truss rod. Tightening the truss rod will reduce the relief and loosening the truss road will increase the relief (if your neck is back bowed or it’s straight and you want to add some relief).
  4. Turn the truss rod only 1/8th of a turn at a time maximum.
adjusting an acoustic guitars truss rod
  1. Retune the guitar – again not just to itself, make sure it’s to pitch – and re-measure. But don’t re-measure straight away. Let the guitar sit for up to a day and then re-measure.
  2. If, after allowing the guitar time to settle, and after again retuning, further adjustments are needed, make the adjustments as necessary. Just remember to never turn more than an 1/8th turn per adjustment.

Only adjust the truss rod if it necessary to do so. This is not a regular maintenance process. However, it may be the case that you need to do it reasonably regularly if you live in places where the humidity changes drastically between the seasons – and depending on the guitar.

If the neck seems to be right then that’s great news you don’t need to adjust it! But what if you’re action still isn’t how you want it? If you’re done with adjusting the nut, then you’re ready to lower the saddle.

Post-Adjustment Checks

After making any adjustments to your acoustic guitar’s truss rod, it’s crucial to thoroughly test and verify that the changes have had the intended effect before considering your work complete. Rushing through this important step risks needing to re-do truss rod tweaks from an imperfect initial adjustment.

  • Carefully examine the guitar neck relief by re-checking the gap between the fretboard and strings, using the same process initially utilized to determine if adjustment was required. The gap should now match your desired relief target, like a standard .007” at the 7th fret.
  • Verify proper neck angle alignment by holding the guitar vertically and sighting down the neck from both the headstock and body ends. The neckline should appear straight, with no visible humps or dips along its length.
  • Test fretboard action height by pressing down strings across several frets, ideally from at least the 1st position up to the 12th fret or beyond. Action should be uniform and suit your playing style, with no overly high or buzzing frets.
  • Check intonation accuracy by matching string tuning at the 12th fret harmonic to the fretted 12th fret note. Adjust bridge saddle positions individually if the tones are sharp or flat.
  • Give the truss rod at least a full day to settle into position before judging the final tweaked state. Re-test relief, action height, and intonation after 24 hours.

Maintaining Over Time

Check neck relief and make minor truss rod tweaks when seasons change. As temperature and humidity fluctuate, the guitar neck reacts. Small adjustments often prevent bigger issues later.

When changing strings, clean the fingerboard grime with naphtha. Condition it a few times yearly with fretboard oil to prevent drying and ensure smooth play.

Watch for back bowing, where the fingerboard arcs away from the strings. This causes fret buzz by lowering string action. If you catch back bowing early, quick truss rod tweaks fix it. Stay proactive.

With routine inspection and incremental truss rod adjustments, your guitar’s playability and tone will stand the test of time.

Final Words

Thanks for reading and I hope this post has helped you to learn how to adjust the truss rod. If you are at all unsure then get a professional to make the adjustment for you. If you are confident that this is something that you can do for yourself then go for it – it’s always nice to learn a new skill.

If you have any further tips or any questions or comments it’d be awesome to hear from you. Just leave a comment in the comments section below.


FAQs Acoustic Guitar Truss Rod Adjustment

Which way do you adjust an acoustic truss rod?

If you are facing the bolt of the truss rod, then the old adage of ‘lefty-loosey’ and ‘righty-tighty’ should see you through the complexities of the process. Put even more simply, if you screw the truss rod’s bolt left, then you will be loosening the action of the guitar and thus lowering the action of the strings overall. Inversely, if you screw the bolt right, then you will be tightening the truss road and, in turn, increasing the action of the guitar.

When should I adjust my acoustic truss rod?

You will know whether or not your truss rod needs adjusting by the state of the strings in relation to the fretboard, there being too much or too little up bow or backbow. This means that the strings are either too close or too far away from the fretboard in certain places, to the point where the sounding out of the notes is either impossible or uncomfortable. Thus, adjusting the truss rod’s tension, whether loosening or tightening, can amend this issue, increasing or decreasing the pressure of the rod in the neck on the proceedings around it.

Which way do you turn truss to lower action?

If you are facing the bolt of the truss rod, then the old adage of ‘lefty-loosey’ and ‘righty-tighty’ should see you through the complexities of the process. Put even more simply, if you screw the truss rod’s bolt left, then you will be loosening the action of the guitar and thus lowering the action of the strings overall. Inversely, if you screw the bolt right, then you will be tightening the truss road and, in turn, increasing the action of the guitar.

Does tightening truss rod lower action?

It is actually the loosening of the truss rod that lowers the action. Tightening the truss rod will achieve the very opposite of lowering the action, tightening the pressure overall, and increasing the action. String height and action overall has far more to do with the nut and the saddle than the neck, however, though a straight neck can make the condition of the action, the string height, and the frets more noticeable. All of these individual parts will need to be working together in harmony.

By Nate Pallesen

Nate is just your average (above average) guitar player. He's no Joe Satriani, Jimi Hendrix or Jimmy Page - wait this site is about acoustic guitars (sorry) He's no Django Reinhardt, Chet Atkins, or Michael Hedges, wait? who!? He's no Robert Johnson, Eric Clapton or Ben Harper - more familiar? Anyway you get the point :-)

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