Ask the Expert: How Does a Truss Rod Work?

Q: I’ve received a lot of emails asking about truss rods: How do they work? How do I know if mine needs to be adjusted? Can it be used to change my action? Can I do it myself?

A: Here’s how it works: Your truss rod is a long metal rod installed in a channel running most of the length of your guitar’s neck. Imagine if you could easily unglue and peel back the fingerboard (oh, but that it were always easy!), just under it, in a contemporary guitar, you would expose a rout filled with a steel rod (sometimes carbon fiber) that is anchored at one end and adjustable from the other. The adjustable side, in the simplest version of a modern truss rod, is threaded and has a washer and a nut on the end. The anchor might be toward the headstock and the adjustable end may be accessed from the inside of the body—like in a modern Martin guitar—or it could go the other way around, with an anchor nearer to the neck joint and a nut accessible from the peghead, as in a Gibson.

Modern guitars tend to have adjustable truss rods, but the concept of a stronger material being built into a neck to reinforce it is not a modern idea. Old Gibson instruments had a strip of ebony glued into the neck for added strength (and handsomeness, of course). Martin necks have had reinforcements for as long as they’ve been making steel-string models—only in the 1980s did their rods become adjustable. In contemporary guitars, the widespread use of truss rods to help keep necks straight means that necks can be thinner, lighter, or even made from cheaper material.

Both good and bad.

Over time, string tension wants to pull a neck forward into a bow shape. The truss rod is almost like one big string counteracting that pull, applying just the right amount of tension in the other direction to pull the neck toward straight. It can be adjusted to get you the right amount of relief in the neck. (Relief is a slight bowing in the neck.) Most techs and players like a little relief, as it allows the string to vibrate freely up the neck and makes playing all over the fretboard more comfortable.

So, is this something you can handle yourself? From where I’m standing behind the bench, I can tell you that it’s usually a bad idea. The first mistake people make is in the diagnostic stage: Maybe their playability has changed, the action has gotten higher, and fretting is uncomfortable. This does not automatically mean the truss rod needs to be tightened! The real culprit is often more complicated: Neck angle and saddle height are relevant, too. Also, making the adjustment is not as simple as it seems—there’s lots to consider. Over-tightening can cause a real problem—rods can break and anchors stop anchoring and small turns can make a big difference.

Also, it can be easy to choose the wrong tool for the job. And while I’ve only talked about the simplest version, truss rods come in more than one variety—some are double action, so you could potentially turn it the wrong direction. Truss-rod adjustments also don’t work for the full length of the neck—most humps, bumps, and dishes cannot be fixed with the truss rod.

Think about it like this: If something changes in the way your guitar plays, it’s time for a setup. That can include adjusting your truss rod, but will likely include other adjustments. And getting a holistic perspective on your guitar is invaluable.

Mamie Minch is the co-owner of Brooklyn Lutherie. She is the former head of repair at Retrofret Guitars and an active blues player.