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I know that you can break a truss rod by over-tightening it. Repair guides warn not to tighten the rod if you meet excessive resistance or hear squeaking noises. For example, from the Fender Bass Guitar Setup Guide:

In either case, if you meet excessive resistance when adjusting the truss rod, if your instrument needs constant adjustment, if adjusting the truss rod has no effect on the neck, or if you're simply not comfortable making this type of adjustment yourself, take your instrument to your local Fender Authorized Dealer.

I also know that some guitars require a little neck relief to prevent fret buzzing, so over-tightening a truss rod has aesthetic risks too.

Are there any other significant risks when adjusting a truss rod? I’m especially interested in any long-term problems that a truss rod adjustment could cause, that might not be immediately obvious at the time of adjustment.

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  • By the way, I’m asking partly in response to this post which hints that there may be risks associated with the truss rod other than the obvious ones.
    – Bradd Szonye
    Commented Jun 13, 2014 at 1:24
  • Just want to point out that fret buzz isn't an "aesthetic" thing.
    – RogerWang
    Commented Jul 18, 2014 at 0:20

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Firstly, all, not some, guitars require neck relief. This is simply because the amplitude of the strings vibration is greater nearer the midpoint of the vibrating length. Of course if the action is set very high this may not cause any problem in the same way high action will hide the effect of poor fretwork or a warped neck etc.

The risks when adjusting a truss rod are:

  • The nut is stuck or you over-tighten and snap/round it off.
  • You loosen it too far and the relief becomes too great and/or the rod rattles.
  • You tighten it too much causing back bow.
  • You tighten it too much and it cracks the neck.

Only the first and last are permanent.

The long term risk is that the last one may not happen immediately. A change in humidity or string tension in the future may cause it to crack weeks or months after the adjustment.

Any neck where the truss rod has caused damage will have had some preexisting defect. If there is no defects present you will be able to over tighten the TR until the guitar is basically impossible to play and not cause any damage. I don't recommend trying it but guitar necks are incredibly strong and generally only fail from impacts or due to defects. My answer on this question is relevant:

https://physics.stackexchange.com/questions/94222/if-a-material-is-built-to-handle-tension-would-removing-the-tension-damage-it/94276#94276

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  • Thanks, this is a helpful answer! I will note however that expert guitar technicians like Dan Erlewine disagree on the need for neck relief for guitars, although they appear to agree with you for bass guitars.
    – Bradd Szonye
    Commented Jun 15, 2014 at 9:45
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On some guitars, it is possible to cause the fingerboard to separate from the neck by over-tightening the truss-rod(s).

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  • Is there a particular kind of guitar, or neck construction, that is vulnerable to this? It would be helpful to know which "some guitars" this affects.
    – Bradd Szonye
    Commented Jul 17, 2014 at 20:03
  • I only know about the guitars I own or have owned, but I was cautioned about this regarding my Rickenbacker 4003 bass. ( I did not actually have any problems adjusting it though.)
    – Hal H
    Commented Jul 17, 2014 at 20:08

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