Deep Dive: Truss Rods
The titles here usually tell you what you’re getting. “Short Takes” are quick hits. “Terminology” explains Rickenbacker-specific lingo. “Overview” covers a model, family, or feature in broader detail. And “Deep Dive” means exactly what it sounds like: we’re going deep. Like, way deep.
I mention that because I usually know what an article is going to be before I start writing it. The title is always the first thing I write. And the first thing I wrote here was “Terminology: Hairpin Truss Rods.”
And then the scope started to creep.
After a couple of days it became “Overview: Truss Rods.” Several days later, “Overview” became “Deep Dive.” Sometimes it just happens like that. Consider yourself duly warned.
At some point in almost any discussion of Rickenbacker minutiae, the term “hairpin truss rods” is going to come up. That’s largely because hairpin truss rods are widely misunderstood and, in my opinion, more than a little bit unfairly maligned. Unfortunately, that reputation makes Rickenbacker ownership seem daunting to some people—and in fairness you do need to know what you’re doing to adjust one…or actually two! But if you do know what you’re doing, they’re among the most stable systems out there. I have a 1977 4001 (click to learn more) with perfect action that I haven’t adjusted since I bought it in 1989.
But if you’re still nervous, fret not—there are plenty of Rickenbackers out there with more traditional truss rods systems. More of those than there are with hairpins, in fact. So how do you know what kind of truss rods your guitar has? By the time we’re done here you’ll know exactly how to answer that question—and hopefully be a little less afraid of hairpins.
Now look, I’ll tell you right up front there is nothing I can really add to the collective knowledge about Rickenbacker hairpin truss rods—or truss rods in general. The information is out there. What I can do, however, is put it all in one place and try to explain it with enough pictures and plain English that it actually makes sense. That’s pretty much the entire mission statement of this site.
So let’s begin by looking at the most common types of truss rods and how they work, because over the years Rickenbacker has used almost all of them in addition to the infamous “hairpin”. Ready? Let’s go!
So why do truss rods even exist in the first place? The answer is string tension. Wood is strong, but everything bends if you pull on it long enough and hard enough. And that’s what guitar strings are doing: constantly trying to turn your neck into a banana by pulling the headstock towards the bridge.
The modern truss rod’s job is twofold: to give the neck additional structural strength—like rebar in concrete—and to mechanically counteract the tension of the strings. So how does it do that?
We begin with the earliest type of truss rod: a simple, fixed metal bar or tube inset into the neck to provide additional structural strength. And that’s all it does. As the name implies, it’s not adjustable in any way, it’s just…there, adding a little extra stiffness to help keep the neck from bowing.
This type of truss rod first appeared in the 1920s and remained in common use through the 1970s—although by then it was generally found on lower-priced guitars like Valcos and Danelectros after adjustable single-action truss rods became widespread in the 1930s and 1940s.
Straight is good, and simple fixed truss rods like these will absolutely help keep a neck straight. But here’s the thing: you don’t necessarily want your neck to be perfectly straight. A little bit of bow, or “relief,” keeps strings from buzzing and allows for lower playing action.
Which brings us to the single-action truss rod, still one of the most commonly used designs today. Patented by Gibson in the early 1920’s, the single-action truss rod provides the same structural strength as a fixed rod while adding adjustability—albeit only in one direction. Hence the name.
Here’s what it looks like and how it works:
A curved channel is cut into the neck—either from the top or the bottom—into which the truss rod assembly (the red, yellow, and blue parts in the diagram above) is placed. The remainder of the channel is then filled with a strip of wood so that the truss rod is held in place at the bottom of that curved channel. The Fender “skunk stripe” is a great example of what this looks like when the channel is cut from the back of the neck.
When the channel is cut from the top, the filler strip is hidden beneath the fingerboard. Note in the diagram above how deep into the neck that channel is at the midpoint—we’ll come back to why that’s important later.
So now let’s talk about the components of the single action truss rod and how they work together. Here are the key parts:
In the photo on the left we have the anchor (yellow in the diagram above), and one end of the rod itself (red in the diagram above). The photo on the right shows the threaded end of the rod, the adjustment nut (blue in the diagram above, and a washer which acts as a thrust plate.
The anchor is set into the neck and the rod is attached to it—sometimes welded, sometimes threaded into place. The anchor can even be just a sideways 90 degree bend in the rod. The job is of the anchor is to keep the rod immovable at one end so the magic can happen at the other end.
At the other end we have the thrust plate and the adjustment nut. The thrust plate caps off the truss rod channel and remains stationary. As the nut is tightened against it, the threaded rod is effectively pulled through the plate. Because the rod is anchored at the opposite end and sits in a curved channel, it naturally wants to straighten as it is pulled through that plate.
As it tries to straighten, it presses upward against the top of the truss rod channel, forcing the neck into a slight backbow to counteract the string tension trying to pull it into an upbow. Put more plainly, the strings are trying to bend the neck one way, and tightening the truss rod bends it back the other way.
So with a single action truss rod, by tightening that nut you can take the neck from this:
To this:
Now let’s go back to that truss rod depth. The reason the rod is buried so deeply in the neck is because a lot of force is concentrated at that midpoint where it presses upward against the top of the channel. You want plenty of wood there to stand up to those forces, so the truss rod has to live fairly deep inside the neck. Overall, it’s a remarkably simple yet effective design.
But here’s the limitation of a single-action truss rod: it can only apply force in one direction. Loosen the nut and the rod simply returns to its relaxed state—but no further. So what happens if the neck already has too much backbow and you actually need more relief?
Now wait just one second! I’ve just explained to you how string tension is constantly trying to turn your guitar neck into a banana, so what causes backbow? Well, leaving a guitar unstrung or with slack strings while the truss rod is still exerting pressure can certainly do it. But far more commonly, wood just moves. Changes in temperature, changes in humidity…wood expands, contracts, and occasionally just decides it wants to be somewhere else. If the grain is predisposed to go in a particular direction—or if the neck and fingerboard woods react differently to changes in the environment—stuff just happens. And a single-action truss rod can’t fix a backbow.
Enter the modern dual-action, two-way truss rod, which became commonplace in the late 1990s and early 2000s. If the single-action rod works by straightening a curved rod to apply mechanical force, the dual-action two-way rod works by bending a straight assembly in one of two directions to apply mechanical force. So how does it do that?
So here we see both ends of a dual action two-way truss rod. It looks quite a bit different. For starters, there’s actually two rods: a flat bar on top and a threaded rod underneath, with the threads running in opposite directions on the both ends. Threaded blocks are screwed onto each end of the threaded rod, and then the flat bar is welded to both threaded blocks. An adjustment screw is then attached to one end. There is no anchor and no thrust plate. The entire assembly is self-contained.
A straight channel—just slightly deeper than the assembly itself—is cut into the neck directly beneath the fingerboard. Unlike a single-action truss rod, there is usually no filler strip; the assembly typically bears directly against the underside of the fingerboard. Because it doesn’t have to live deep within the neck, the neck itself can be made thinner—one advantage of this design. Another is serviceability: the entire assembly can usually be slid in and out of the channel without removing the fingerboard or requiring any special tools.
Turning the adjustment screw clockwise causes the two threaded blocks to move closer together. This forces the flat bar to bend upward, pressing against the underside of the fingerboard and inducing backbow—just like the single-action truss rod. Turning the adjustment screw counterclockwise moves the threaded blocks farther apart, causing the assembly to bend downward instead. This applies pressure to the bottom of the truss rod channel and induces upbow. It’s a brilliant design.
Let’s take a moment to unpack the term “dual action two-way” because it’s really describing two different concepts. “Dual action” refers to the fact that the assembly consists of two components working together, unlike a traditional single-action truss rod. “Two-way” because, well, it actually adjusts in two directions, allowing you to either reduce or increase the amount of bow in the neck.
I make this point because when we talk about the Rickenbacker hairpin truss rod—which we’re finally going to do right now—you will see that by this definition it is actually a dual-action truss rod even though it’s technically made from a single piece of metal. A diagram probably makes that easier to understand:
We start with a long bar, folded in half like a hairpin—hence the name. One leg is slightly longer than the other and threaded. A large aluminum spacer, or thrust block, is slid onto the threaded end and held in place between the shorter leg of the rod and the adjustment nut. Just like our dual-action two-way truss rod, the assembly sits in a channel cut immediately below the fingerboard. Tightening the nut pushes the shorter leg against the thrust block, forcing it to bow upward against the underside of the fingerboard and induce backbow. This creates the mechanical force needed to alter the neck’s relief.
Now, like a single-action truss rod, it only adjusts in one direction. Loosening the nut will not cause the rod to bow in the opposite direction—it simply returns to its relaxed position. So dual-action, but not two-way.
So why is that so daunting to so many people? Because the adjustment process is completely different. With single-action and and dual-action two-way truss rods, you turn the adjustment nut until the neck reaches the shape you want. Easy enough. With Rickenbacker hairpins, however, you first move the neck into the position you want by hand, then tighten the truss rods to lock it there.
Wait, what? Yup. You’re going to use your hands to move the neck to the position you wanr, hold it there, then tighten the truss rods to keep it there. Treat it like a conventional single-action truss rod, however, and the forces involved can pop the fingerboard loose, remove it entirely, or even crack the neck. Ever wonder why you see so many older Rickenbackers with repairs that indicate this type of damage?
More often than not, it’s because someone didn’t understand how the system works. (And yes, I know that at least one of you knows all too well that this particular guitar had modern truss rods, but it’s a good illustration of what the damage looks like.)
Now I’ll admit that all sounds pretty scary. Bending the neck with your hands? Don’t worry. The neck is stronger than you probably think it is—especially on the neck-through (click to learn more) models like the 4001 and 620 (click to learn more). With set-neck semi-hollow bodies like the 330 (click to learn more) or 360 (click to learn more) however, you do want to support both ends of the neck when you’re working while you’re making adjustments so you’re not placing unnecessary stress on the neck joint. The neck itself, though, is generally more robust than people give it credit for. And once it’s set, you’ll likely find the system to be remarkably stable.
For what it’s worth, even with other truss rod systems it’s helpful to give the neck a little manual assistance making adjustments. If nothing else, it takes some load off the rod and makes the adjustment nut a little easier to turn.
So that’s an overview of the types of truss rods you’re likely to encounter on a Rickenbacker. But before we get into figuring out what you have, I let something slip above when I said “truss rods”—plural. Because for much of their history most Rickenbackers had not one but two truss rods.
Why? Well, it’s a little telling that the first instrument to officially feature two rods was the 4000 bass. Designer Roger Rossmeisl’s (click to learn more) rationale was that having twin rods allowed for slightly different amounts of relief—and therefore slightly different action—on either side of the neck to improve playability. Given the large disparity in diameter between the low E and high G strings, and the difference in tension between the two (up to 10-15 pounds more for the higher strings), you can kind of see how that might make sense.
Other key reasons often cited include the additional structural strength an extra rod imparts—and given how slim vintage Rickenbacker necks were compared to their single-action equipped contemporaries, that’s probably a pretty legitimate concern—as well as the ability to correct a twisted neck. Here’s a pretty extreme example:
While a twist that severe would likely also require heat and clamps to correct, milder twists can often be corrected with manual pressure and the truss rods alone. Ask me how I know!
Rickenbacker believed strongly enough in the benefits of the dual rod system that it remained in use for over sixty years. Unfortunately, having two rods to adjust—and adjusting them in a completely different manner than most other guitars—convinced many players that the whole system was unnecessarily complicated and finicky. That’s probably not entirely fair, but it is nevertheless the perception.
So now that we understand how all the various truss rod systems work—and why Rickenbackers had two of them—let’s figure out how to tell what a specific guitar actually has. We’ll go chronologically, because apart from transition periods that’s usually enough. But for those transition periods—and just because it’s useful to know in general—we’ll also look at how to visually identify the various truss rods Rickenbacker has used.
The twin truss rod concept was there from the start, with prototype Combo 600 and 800s (click to learn more) featuring two through-body rods—although production instruments would make do with just one.
But the hairpin rod itself also appeared very early in the timeline. Did those very first Combo 600s and 800s have hairpins? I haven’t been able to confirm. By the time the Combo 400 (click to learn more) launched in 1956, however, they definitely did—as would all subsequent models, even if some had only one rod instead of two.
While most guitars from this era have a neatly routed channel for truss rod adjustment access, you’ll also find some Capris with a decidedly more crude Forstner-bit channel!
Note how these early single truss rod models originally used an oversized nut as the thrust plate before the larger aluminum thrust block we discussed earlier was introduced in late 1960/early 1961. When dual truss rods officially debuted on the 4000 (click to learn more) in 1958 they too initially used the oversized nut thrust plate system.
All solidbodied guitars would transition to twin rods in 1960. Semi-hollowbodied guitars would follow in 1961 with the launch of the redesigned “New Capri” models. Note that the original semi-hollowbodied Capri models never had two rods. Along with the dual truss rods came a single thick aluminum thrust block. This design would remain effectively unchanged for over twenty years.
The first change of note would come in 1979 when the 4003 (click to learn more) launched. The change wasn’t what you might expect. After all, the entire rationale behind the 4003 was to beef up the 4001’s neck so it could better withstand the tension of roundwound strings. So how did they attempt to accomplish that? By flipping the dual hairpin truss rods around so they adjusted from the body end of the neck instead of the headstock for…reasons?
Note how the thrust plate is split into two pieces and the adjustment nuts are smaller on many of these guitars with “backwards” hairpin rods—presumably to avoid interference with the neck pickup. Also note that these “backwards” rods only appeared on the 4003. All other guitars remained unchanged.
You will find it written all over the internet that the 4003 launched with an entirely new truss rod system, but as you can see, that’s simply not true. The good news is that these early guitars are pretty easy to spot. To make adjustment easier, the pickguard was split into two pieces so you wouldn’t have to remove the entire pickguard to adjust the truss rods.
You can also identify these hairpin-equipped guitars by removing the truss rod cover. There you will find extensions of the truss rod channels to allow the rods to be installed…and that’s it. No large routs, no anchors, no hardware peeking out at you.
The backwards hairpin truss rods were really just a brief detour on the road to the first major change in Rickenbacker truss rods in almost thirty years. That change finally arrived in 1984 when the 4003 transitioned from dual hairpins to dual-single action rods.
You already know what you’re looking at here—there’s just two of everything except the thrust plate. Two rods, two adjustment nuts, and two anchors composed of a toothed lock washer, a nut, and a domed acorn nut.
But adjustment wouldn’t return to the headstock just yet. It would take until mid 1985 for the rods to be turned back around. That means you have to look a little more closely at 1984-85 4003s to determine what type of truss rods they have, because those transitional guitars still have the split pickguard. The easiest way to identify these transitional guitars is to remove the truss rod cover.
Instead of the threaded rods, adjustment nuts, and thrust plate we’d expect to find here, we find the anchors with their distinctive acorn nuts instead. All of the adjustment hardware is still located at the tail end of the neck.
Once the rods were turned back around the “right way”, the split pickguard disappeared in mid 1985. I’d still take a look under the truss rod cover on any 1985 4003, though, just to confirm what you have.
That said, it can be a little difficult to tell the difference between the two truss rod types just by looking at the adjustment nuts. There are two other things to look at, however, that will clear things right up though—and this holds true for all guitars, not just the 4003 (spoilers!).
So first let’s look at the old hairpin rods:
As the photo highlights, the thick aluminum thrust block is an immediate giveaway. And because hairpin truss rod channels are left uncovered, we can also see both the ends of the channels and the rods themselves.
Guitars with single-action rods have a thinner, steel thrust block and, because the truss rod channels are filled with a wood strip, we can’t see the rods themselves.
This is a good point to remember just how much deeper into the neck single-action truss rods are set. When you hear people talk about how much beefier 1980s 4003 necks feel when compared to 1970s 4001s, now you understand why. The 4003’s single-action rods had to live much deeper inside the neck, and the 4001’s famously slim neck simply wasn’t thick enough to accommodate them.
While I may have spoiled it already, over the course of 1984-85 all guitars transitioned to dual single-action rods, although the exact timeline remains unclear. So if you’re looking at a 6-string or 12-string from 1984-85, you really just have to check. One way to know for sure what you have is to remove the truss rod cover, take a peek, and compare what you see to the examples above.
But the easier way is to look at the other end of the neck. On guitars with the single action rods you’ll find two large holes in the base of the neck below the fingerboard for the recessed anchors—with two shiny acorn nuts peeking out at you.
And on guitars with hairpin rods, the truss rod channels at the base of the neck are smaller and closer together, with no visible hardware.
And while these tips are especially handy in sorting out transitional era 1984-1985 guitar, they actually hold true for any guitar made between 1961 and 2024. Oops, another spoiler!
But before we explore that, I’m going to say something provocative. John Hall and period literature and the user manual all referred to the new single action truss rods as two-way. But they’re not. They’re just not. I’ll lay it out like this. For a truss rod to truly be two-way, there should be a neutral position with no tension at all on the assembly. From that neutral position, turning the adjustment nut one way should induce backbow, while turning it the other should induce forward bow. If you turn the Rickenbacker truss rod counterclockwise from neutral position it will not induce a forward bow. The nut will just come off the rod.
So why did Hall, the literature and the user manual refer to it as “two-way”? Artistic license, I’d say.
You see, when a guitar leaves the factory the nuts aren’t in a neutral position. They’ve already been tightened somewhat to induce some amount of backbow. Backing the nuts off therefore reduces that backbow, at least until you return to neutral. So there is technically some adjustment the “other way”…but only back to neutral. I suppose if you squint hard enough, you could interpret that as adjustment in two directions, but I don’t. Because it’s not. Rant over!
Now while everybody thinks “hairpins” first when Rickenbacker truss rods come up, the single action truss rods actually had a longer run when you do the math. But their era would begin to end in 2019 with the launch of the Al Cisneros 4003AC Signature Limited Edition (click to learn more) which featured—for the first time since 1961–a single truss rod and—for the first time ever—a dual-action two-way truss rod.
While the first 4003ACs retained the existing—and now comically oversized— truss rod adjustment channel rout on the headstock, it didn’t take long for a simpler, more appropriately sized rout to appear.
In addition to the 4003AC, the new single truss rod started appearing on special run 4003s in 2020—like the Andy Babiuk guitar above—but the twin single-action rods would remain the default until 2022. At that point, the single rod became standard on all basses. Not coincidentally, at around the same time the 4003 neck became much slimmer—you no longer needed a thick neck to accommodate deeply buried curved single-action truss rod channels.
Funnily enough, right around this time you started seeing complaints—for pretty much the first time—about brand new guitars with twisted necks. Kinda ironic that there were suddenly complaints about something that could no longer be corrected with truss rods adjustment alone, no? Maybe Rickenbacker had been right all those years about the additional stability that second rod delivered…
In 2024 guitars got the single truss rod as well. Rickenbacker’s double truss rod era was over.
Well…with a couple of exceptions.
In the name of “historical accuracy”, the reissue 325C64 and 360/12C63 (click to learn more) continue to feature twin truss rods. But historical accuracy only goes so far—these guitars utilize the “modern” single-action truss rods rather than the hairpins their namesakes originally came equipped with.
Similarly, the 325V59 and 325C58 (click to learn more) featured only a single truss rod during their respective runs because 1958 Capris were originally built that way. But once again, Rickenbacker opted for a modern single-action rod rather than a hairpin.
So where does all of this leave us? Hopefully with one less thing to be afraid of. Hairpin truss rods aren’t fragile, mystical, or inherently flawed—they’re simply different. And once you understand how they work, identifying and adjusting any Rickenbacker truss rod becomes pretty straightforward.
More importantly, you should now be able to tell exactly what type of truss rods a given guitar has, understand why Rickenbacker changed them over the years, and appreciate that there was usually a pretty good engineering reason behind those changes—even if the company occasionally took a detour or two along the way.
That’s probably more than anybody ever really wanted to know about Rickenbacker truss rods. But if you’ve made it this far, you’re exactly the kind of person this site was built for. And there are plenty more rabbit holes to fall down in the Rickenbacker101 Archive.
Best article on RiC truss rods I’ve seen. Thanks for the time and effort to put this together.
Great and actually really concise article (if you think about all it covered).
The beheaded ‘57 4000 headstock photo added a dramatic touch of horror! 😅