Adjusting the truss rod

To hear a lot of people talk, you'd think that the long, thin piece of metal we call the truss rod was a cross between the Holy Grail and a Plutonium fuel rod. Yes, you do have to take care when adjusting it and it can break, but if you approach the task with a little respect for the rod and some common sense, there's no reason why you can't do this job yourself. Having said that, if you're in any doubt as to what you're doing, then leave the job to a competent guitar tech. It isn't the most difficult adjustment in the world, and, provided no work is required on the frets, should be quite inexpensive.

The truss rod is essentially a long metal rod that is inserted into the neck of the guitar and fixed. Tightening and loosening in it flexes the neck and allows curvature to be applied to the neck, altering its characteristics and, hence, its playability. Before I describe this adjustment, a few caveats.

1) It may be, that after adjustment, the neck isn't quite right and you may need to look elsewhere to solve the problem. The frets may need stoning, for example, which is outside the scope of this series of tutorials.

2) Try and get hold of the factory spec for your guitar - Fender actually have theirs here - and see how a standard truss rod set up suits you. It's a good basis on which to start, and you can always deviate from it.

3) Be aware of the advantages and benefits of the various sorts of "action". A very low action means that bending is slightly more difficult and the sound has less body. On the other hand, the strings are much easier to fret. With a high action, the reverse is true. I know that there are a lot of SRV fans out there, and he played with   very high action, which explodes the myth that a low action is always the one to shoot for.


When to check the truss rod

The rod needs to be checked whenever you string the guitar, although if you use the same strings - brand and gauge - you can make the checking intervals a little further apart. Also, because wood and metal expand and contract according to temperature and humidity, you may find that the neck shifts according to these factors. Also, if you become aware of buzzes that weren't previously evident, it's a good idea to check the neck.


How to check the truss rod

Rest the curve of the bass bout on the floor, and sight down the neck towards the body, looking along the edge of the fretboard. then flip the guitar over onto the treble bout and repeat the operation. Observe how the line along the edge of the fretboard runs. If it seems to curve so that it bulges out away from the body, the neck has a backbow. If it runs the opposite way, the neck has relief. (For those of you who are familiar with trussrods, I know that there are other conditions that I haven't mentioned, but I haven't got the time to write a book on the subject. I'm just outlining the most common truss rod states.) It may be that you see that the neck is dead straight, of course.

So, to sum up. you have three main neck states:

a) relief

b) backbow

c) dead straight

Here's a pathetic diagram I drew to help you visualise them.

neckdiag.gif (13063 bytes)

If the neck is dead straight, and you have no buzzing and you like the way it feels, it's pretty safe to assume that your truss rod is adjusted just right. Most techs try and shoot for a straight neck. Even if you have a little buzzing, if you don't hear it when it's plugged in - assuming that it's an electric, of course - then you can leave it. Not all buzzes will sound through the amp. If it still buzzes when plugged in, then this doesn't necessarily mean that it's the truss rod that requires adjustment. You might find your problem is solved by raising the bridge or bridge saddles. If this doesn't work and you don't eliminate buzzing by adjusting the rod - more on that below - then you may need some attention to the frets.


(The lesson to be learned here is that all the various stages of adjustment - the nut, the bridge, the rod, etc - are interdependent and adjustment of one of these factors on its own may not be sufficient to achieve the set up you're after.)

If the neck has some relief and you're happy with it, then you can leave it alone. However, if the relief is too pronounced, causing a very high action which causes intonation problems when you fret a note, then the neck will need straightening by tightening the trussrod.

If the neck has a backbow, this can cause some of the higher notes to fret out. You may find that when you play say, the B string at fret 5, the string is fouled by the higher frets and the sound of the note isn't clear. The truss rod will then need to be loosened to apply some relief.


Where to adjust the truss rod

This differs from one guitar to another according to brand, model and type. Gibsons have the adjustment end of the rod under a small plate on the headstock. Some Fenders have the business end here as well but with no plate. Others have the adjustment end where the neck joins the body, in which case you have to remove the neck to adjust it and keep on fitting it back and taking it off until the rod is right. I'm not going to deal with such adjustment here. Some acoustics have the adjustment area inside the guitar where the neck joins on. There are also various methods of adjustment. Some rod ends have a screw slot, some a nut, and others a hex slot. So, you'll need a screwdriver, a socket of some sort or a hex key. Obtaining the right hex key can sometimes be a problem, but the right one's out there somewhere!


How to adjust the truss rod

OK - this is the moment you've all been waiting for!

Using the right tool and a well-fitting one as well (you don't want to mess up the slot or nut shoulders!) insert it into the truss rod end.

If you want to apply relief to the neck you loosen the rod by turning the rod end - the nut, slot, whatever - to the left, or anti clockwise. 

If you want to straighten the neck and eliminate backbow, tighten the rod end to the right or clockwise.

Remember - "righty tighty"!

Apply a one-eighth turn at a time and sight the neck as described above. If the neck is how you want it - stop! If not, apply another one-eighth turn and sight it again. Repeat until the neck looks right.

If the rod won't shift, don't keep on trying to turn it. Take it to a guitar tech. Similarly, if it squeaks or grates, leave well alone and take it to - you've guessed it! - a tech.

The biggest danger is over tightening. In this case, the worst scenarios are stripped threads on the rod, or even a snapped rod. In such cases, the repair can often be more expensive than buying a new guitar. However, you have been warned! If you're in any doubt about your own competency to do this job, take your guitar to a tech and if you encounter a truss rod that won't co-operate, do the same!

Just use a little care and common sense and you should be OK.

I realise that this tutorial is little more than an outline. However, for those of you who want to learn more about this aspect of guitar maintenance and everything else you can do yourself, the best book I've found is "Guitar Player Repair Guide" by Dan Erlewine. It's a fantastic book with lots of tips and practical advice from a guy who has looked after some of the greatest players' instruments.

Good luck!


Guitar set-up tutorials - Overview

Tutorial #1 The tools you need

Tutorial #2  Stringing your guitar

Tutorial #3 Setting the intonation

Tutorial #4 Adjusting the nut

Tutorial #6 Minor maintenance jobs

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