Aligning A Jazz Bass Neck

My answer to Eric was simple: “Pack it really well and ship it to me. I’ll take it from there.” The bass arrived several days later.

Fig. 1 Aside from a few nicks and battle scars, the bass is pretty clean. The look of the maple and white binding against the black finish is striking!

Usually, the neck can be realigned by slightly loosening the mounting bolts and pushing the neck in the opposite direction (toward the bass side in this case) while re-tightening the bolts. This one needed more than that.

Fig. 2 The neck wouldn’t shift to the bass side, even though I could slip a .007" feeler gauge between the neck and body.

Fig. 3 Upon removing the neck, it was clear to me that someone had previously tried to solve this problem by removing a little wood from the neck cavity’s bass side (which explains the gap that the feeler gauge slipped into). Whatever the intent, the fix didn’t work. The person should have removed a little more wood, on an even taper, along the bass side of the neck cavity to create space for the neck to shift toward. I chiseled away a little more wood from the bass side and smoothed it flat with a file. I knew I wouldn’t have to remove much wood for the neck to shift right on target.

Fig. 4 Next, rather than bolt the neck back on and call it fixed, I fixed another issue that Eric wasn’t aware of: Like other J-Basses built between 1975 and ’81, his Jazz was equipped with Fender’s Micro-Tilt neck adjustment system. These instruments, identifiable by their three-bolt neck plates and “bullet” trussrod adjusters, have a steel set screw mounted in the neck cavity that bears against a small steel plate screwed to the underside of the neck heel (visible in Fig. 3). Turning the set screw with an allen wrench allows you to adjust the neck angle—instantly raising or lowering the string height. Cool! However, what I don’t like about the Micro-Tilt is that using it keeps the underside of the neck heel from being in direct contact with the body. Instead, the neck sits on the set screw, leaving an air space between the neck and body. That single point of contact not only harms the tone, it also creates a weak area for the neck to sag into under the pressure of the neck-mounting bolts.

Along with sagging and clamping issues, the neck heel has three mounting-screw holes drilled into it; it’s not unreasonable to think that the maple neck could absorb moisture through these holes and swell a little. All of these forces can add up to a visible and irritating hump in that end of the neck, which can cause fret buzz. Instead of relying on the Micro-Tilt to set the perfect neck angle, I prefer to make a tapered shim (or shims in this case) that fills the air space and supports the neck heel with full contact.

Fig. 5 I used a tapered mahogany shim for support in the back end of the cavity where the air space was as much as 3/32", and I filled the remaining air space with several strips of 180-grit drywall sanding screen. In the photo, you can see the wood shim, with two strips of screen on top, and one strip of screen about 1" back from the front edge of the cavity. This setup creates a tapered shim, with the screen gripping the wood of the cavity and the underside of the neck heel, which will help keep the neck from shifting once the neck is bolted in place.

The neck aligned perfectly when I bolted it back onto the body. The shifting problem was solved, but I wasn’t done, yet.

Fig. 6 There was an open split in the center of the fingerboard that ran from the first fret pearl inlay to the nut. We’ll look into that next month.