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 neck is set how it should be before you do any adjustments to your nut or saddle.
It might also just be because your 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.
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 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 a 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 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 inches (0.18mm) when the strings are compressed at the 1st and 14th frets. So it’s only very very subtle.
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-check the next day and make another small adjustment if necessary and so on until it is right.
As is mentioned in the video above, the truss rod adjustment isn’t a cure for action in itself. 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 cover at the headstock end (usually you can get in there via a few screws)
The adjustment of the truss road 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.
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
- Remove the cover on the headstock (if your access is via the headstock)
- 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!
- 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).
- Turn the rod only 1/8th of a turn at a time maximum.
- 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.
- 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? Then you should look at adjusting the nut first and then the saddle.
Thanks for reading
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.