Wildly Fluctuating Action

[tkersey]

I bought a Martin GPC 15ME Streetmaster a couple of months ago. After a few weeks I noticed the action was high so I took it to a shop for a set up. About a week later it started buzzing when I used a capo. I took in to another shop for a set up. A week or two later the action was once again high. I adjusted the truss rod myself. The action has gone up again. I tried adjusting the truss rod and after doing that when I retuned it the action was high again. This is the first guitar I’ve owned that retails for over 1,000. I’ve been told that guitars made of nicer tone woods are more sensitive to humidity so I keep it in it’s hard shell case when I’m not playing it. Does anyone have an idea what might be happening?

[Rev Roy]

Are you monitoring the humidity with a hygrometer in the case? That would help rule in/out a humidity issue.

[Rosewood99]

It sounds like something more than just average humidity changes. Perhaps there’s something wrong with the neck or truss rod. Are you sure you’re adjusting in the correct direction?

[M Hayden]

The truss rod’s not for adjusting action - it’s for adjusting the amount of relief in the neck.

As others have said, check the humidity and the geometry. It’s possible that the instrument is deforming or the neck is coming loose or something....

[tkersey]

Thank you both for your insights!

I haven’t had a hygrometer but I have used silicone packs to mitigate the considerable humidity we’ve had here as of late.

I’m definitely turning the truss rod in the right direction. The thing that really has me concerned is that the action gets high again after I retune it.

I called the place I got it set up and he said that’s just the way of the world. I emailed Martin and got an auto reply. Hopefully they’ll get back me on Monday with something helpful.

[mtdmind]

I had that problem with my guitar. I had sanded down the saddle to where the action was good and days later the action would be bad again. For my guitar, I took the bridge off and reglued it.It has been perfect and consistent since.

[phavriluk]

Have any of these guitar techs been taking a look at how much (or whether) the top is displaced?

[tkersey]

Originally Posted by phavriluk

Have any of these guitar techs been taking a look at how much (or whether) the top is displaced?

No they haven’t.

[Napman41]

Put down your truss rod wrench and measure the humidity in the space your guitar lives in. You’ve got a humility problem.

[RonMay]

Stop adjusting the truss rod trying to change the action. That's not what it's for. It's for adjusting the relief in the neck... nothing more.

The right way is to adjust the saddle.

On another note, techs are not luthiers. Take it to a qualified luthier to get his insight on your problem.

Ron

[MThomson]

Originally Posted by RonMay

Stop adjusting the truss rod trying to change the action. That's not what it's for. It's for adjusting the relief in the neck... nothing more.

The right way is to adjust the saddle.

On another note, techs are not luthiers. Take it to a qualified luthier to get his insight on your problem.

Ron

While this is true, if the guitar has been set up and has had good action, the saddle and nut height are unlikely to change and the relief is likely responsible for humidity related changes. That's why the erroneous relationship between truss rod and action is established. However, it would be worth measuring relief when making the truss rod adjustments to confirm you're going the right way. If your relief is good and action keeps changing you have structural issues.

[Peter Z]

I totally agree with MThomson.
Of course the relief changes the action. If the relief changes, truss rod adjustments are the way to go. Nevertheless you should watch the humidity to avoid (most of) the relief fluctuations.

[JayBee1404]

When a guitar’s action rises, there are a number of factors which could be contributing to that change and, in order to decide on the correct treatment, it’s necessary to diagnose what has caused the change. That means having a set of measurements from the guitar - a ‘baseline’ - after a satisfactory set-up, and taking another set to compare when a change is perceived. I personally measure and record the neck-relief and 1st-fret action, the 12th-fret action, the height of the strings above the top immediately north of the bridge, and the amount of top-belly immediately behind the bridge. If any of those numbers change, I have a clue as to what is going on with the guitar.

I also have hygrometers in the rooms where my guitars live, and also in their cases. The outdoor RH in your area according to the weather forecast is pretty meaningless indoors in your house, where CH, wood-burners, A/C etc. can all have an effect on the RH in which your guitars live and, without the means to measure the actual RH they are subjected to indoors, you’re just guessing.

I’m always surprised that, as a first reaction to an action change, people start swinging on a truss-rod wrench without knowing whether the relief in the neck has actually changed. If the relief is stable, but 12th-fret action is rising, there must be something else happening, so attacking the truss-rod isn’t the answer. In that case I check the string-height above the top in front of the bridge and the amount of top-belly behind the bridge. On the other hand, if the relief has changed, I adjust and set it back to the ‘baseline’ number, then check the rest of the measurements against ‘baseline’.

I live in the UK where we have a fairly temperate climate - cool, wet winters and warm, wet summers - and my experience of the effect of RH fluctuations on my guitars is that the top, being thinner and more flexible, is perhaps affected more, and more quickly, than the neck. In fact, after the first couple of set-ups, I almost never need to adjust the neck-relief again, other than for string-gauge changes (and even then, not always).

Without more detailed information, it’s not really possible to diagnose the OP’s problem. If it were my guitar, I would take it to a good set-up tech or luthier and have it assessed/set up. Then I’d take measurements and record them so that, if things move again, I’d have some data on which to base my diagnosis and the appropriate action required.

The usual disclaimers apply......IMHO, YMMV, I’m not a luthier, just an enthusiastic amateur, etc.

[Silly Moustache]

Hi, it occurs to me that you may be using the truss rod far too energetically.

most adjustments can be made by a 1/8" turn, or about 20 degrees (or, from 12 to 1 or 11 - visualising a clock face).

Also truss rod adjustments don't always take effect immediately and may take 24 hours to show the alteration that ha been made.

I suggest that you measure the action at 12 the fret, and the relief as normally measured - capo on fret one, hold down string at 15th fret and measure at 7th fret (with feeler gauges).

NOTE - if you are going to do your own adjustments, you need the appropriate tools and a certain amount of knowledge. (I'm not being pompous - as I've made every mistake there is regarding this sort of thing).

[Silly Moustache]

Hi, it occurs to me that you may be using the truss rod far too energetically.

most adjustments can be made by a 1/8" turn, or about 20 degrees (or, from 12 to 1 or 11 - visualising a clock face).

Also truss rod adjustments don't always take effect immediately and may take 24 hours to show the alteration that ha been made.

I suggest that you measure the action at 12 the fret, and the relief as normally measured - capo on fret one, hold down string at 15th fret and measure at 7th fret (with feeler gauges).

NOTE - if you are going to do your own adjustments, you need the appropriate tools and a certain amount of knowledge. (I'm not being pompous - as I've made every mistake there is regarding this sort of thing - and still don't consider myself totally competent to do set ups).