The truss rod in your guitar lives there to help keep your instrument’s neck straight. Equipped with steel strings, electric and acoustic guitars endure enough string tension to bow their wooden necks. They develop a curvature as the headstock, where the strings terminate, get pulled, and the neck begins to bend.
Truss rods themselves do not loosen inside the guitar’s neck. A truss rod may need continual adjustment, but this is not due to loosening or turning on its own. The curvature and bend can be countered by turning the truss rod, also known as “tightening” the rod.
Because a neck bow causes the strings to rise up and away from the fretboard, the truss must be attended to in order to stop this from happening. The farther they get from the fretboard, the harder they will be to push down on. Additionally, you will encounter tuning issues with even the slightest bow.
How Truss Rods Work
A truss rod is a metal rod resting inside a hollow in the guitar neck. Being made of metal and much less malleable than wood, the neck is significantly less prone to give in to the pressure coming from the strings. The truss rod, then, acts as a support for the neck.
Depending on your guitar, the nut you turn the truss rod with may be located at the headstock end of the fretboard, or at the other end, near the pickups or soundhole. Turning the truss rod (usually with an Allen wrench. I recommend the Jim Dunlop Multi System 65 Guitar Tools from Amazon.com – it’s a must for every guitarist) applies counterpressure to the neck’s wood and can eliminate some of the neck’s bow.
A quick note about the tool you use: some truss rods require their own proprietary wrench. Be sure you use the right tool or the correct size of Allen wrench. If you strip the nut by using the wrong tool, high-dollar repairs will be in your immediate future.
Nearly every acoustic guitar, electric guitar, and electric bass has a truss rod in its neck because the steel strings on them exert an immense amount of pressure on the neck. Classical guitars generally do not have truss rods with their nylon strings because the strings do not exert enough tension to make them necessary.
Single vs. Double Truss Rods
Most instruments use single truss rods, which are essentially one piece of metal inside the neck. Some use a double truss rod system. Having two truss rods in the neck of the guitar means two things: you’ll be able to adjust for back bowing (if the neck is bending away from the guitar and creating a convex arc in itself), and you’ll have a second rod in the neck to counteract the string tension that much more.
Which one you use depends on what’s in the guitar you purchase, though few guitarists base their instrument choice on the number of truss rods. A luthier building a guitar for you might ask if you want to specify, but in general, you get the truss rod system that you get, and it’s usually a single.
Using the Truss Rod
So you’ve noticed that the strings on your guitar or bass seem to be getting farther away from the fretboard, or perhaps you can see that the neck is bowing inward. Maybe you’re just having problems playing in tune and aren’t sure why.
The chances are good that you need to adjust your truss rod. First-time adjusters may be trepid about wrecking their instrument, but truss rod adjustment, if done with care, should cause neither you nor your guitar any problems. Done correctly, it will improve your playing experience.
Accessing the Truss Rod
If your truss rod’s adjustment nut is at the headstock end of your guitar’s neck, you will most likely be able to see it and access it. Some electric guitars have a cover over the adjustment nut, which is easily removed with a small Phillips-head screwdriver.
If your adjustment nut is at the other end of the neck, you may need to remove your pickguard to have full access (older guitars sometimes require removing the neck from the body, which really complicates things when it comes to checking whether you need more adjustment).
Once you’ve accessed the nut, be sure you have the appropriate tool, and now we’re ready to move on to an actual truss rod adjustment.
Performing an Adjustment
Before we start, a critical piece of information: do not ever turn the truss rod more than a quarter of a turn at a time. Doing so is a great way to cause lasting damage to your instrument. Many luthiers recommend no more than an eighth of a turn at a time.
Remember that the wood of your guitar is soft, but it isn’t putty. If you introduce too much of a change to the shape of the neck, you could crack or otherwise damage it.
Make a mark on the nut so that you will know from where you started your adjustments. This will help you discern how much an eighth or a quarter of a turn is, and if you need to reset things, you’ll have a record of the nut’s original position before you started tinkering.
The old “righty tighty, lefty Lucy” adage applies here, but you do need to know which way is which when you want to change the shape of the neck. If your neck is bowing upward – which is to say, bending in the direction the string tension pulls it – you’ll want to tighten the rod, so you’ll be turning it to the right. A back bow, on the other hand, necessitates a left turn. So:
- If your guitar’s neck is concave, turn the rod to the right.
- If your guitar’s neck is convex (a much less common issue), a left turn is called for.
- Neither turn is appropriate for adjusting string height (or “action”).
After your first (very small) turn, the bow in the neck will almost immediately change, though it may take some time for the change to settle in fully. Some people recommend waiting 24 hours or so before playing the guitar, and others say play away immediately.
There is no consensus here, but common sense tells us that the bigger the adjustment, the longer the guitar will take to settle into it fully. You’ll need to check your tuning after even the slightest adjustment, as it will be off otherwise.
Do Truss Rods Loosen Over Time?
Truss rods do not loosen over time. The need for continued adjustment over months and years of playing an instrument arises not from the rod itself loosening but from many other factors.
These include the string tension, changes in weather and humidity (think of that door in your house that’s harder to close in the summer – higher humidity makes the wood swell, including the wood in your instruments), even the type of wood from which the guitar is made.
One of the indicators of a guitar’s need for a truss rod adjustment lies in the string height. When you notice that the strings seem way farther away from the neck than they used to be, it’s probably time to think about a truss rod adjustment.
Players should not misconstrue this information to justify making adjustments to string height using the truss rod. Strings sitting too high or too low (creating fret buzz) is a symptom of neck bowing issues, and the change in their height is simply a side effect of adjusting the truss rod.
If you wish to adjust your string height, you do that at the bridge of your guitar. Acoustic guitars have a one-piece plastic or bone saddle under the strings, and changing their height can be an arduous process involving files or sandpaper. Most electric guitars have a multi-piece metal saddle system in which each string height is easily adjusted with a tiny Allen wrench.
Again, truss rod adjustment is not the way you set up your guitar or change its action. If you want those changes, deal with them at the bridge, or take your instrument to a guitar tech and have him adjust it for you.
Can I Over-Tighten My Truss Rod?
You can over-tighten your truss rod. Tightening too much will cause a back bow, which will result in a hump in your guitar neck. Cracking the wood in the neck is also a possibility, and that would be disastrous. Breaking the truss rod requires expensive repairs.
Never turn the adjustment nut more than one-quarter of a turn at a time. Instead, make small adjustments, then check the results before you make any more. In general, if you make small turns and never force anything, you should be fine. If the rod doesn’t turn easily, brute force isn’t going to help anything.
The truss rod exists to help keep the guitar neck straight and true. Without it, string tension causes the neck to bend, making the instrument harder, if not impossible, to play. While your truss rod may need adjustments, it will not be due to the rod coming loose.
Instead, the continued need for adjustment results from high string tension and environmental factors. Thankfully, the adjustment process is simple and effective, though you do need to be careful. Most of us love our instruments dearly, so we know to treat them well, and this applies to adjustments, as well.