From the November/December 2021 issue ofAcoustic Guitar | By Martin Keith

Q: I have a 1958 Martin D-28. During a recent restringing, I noticed the tuning gears (Grover Rotomatic 102C) had all sorts of black goop inside, looking like lubricant past its service life, when I removed the tuning button from one of the gears. I'm wondering if after 63 years of good service these gears might need cleaning, relubrication, or repacking. I've read a little about it and have been warned off using Vaseline and seen that Tri-Flo Superior Dry is recommended by some. What would you use for lubrication to renovate a Rotomatic? —Bob Metzger

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A: To begin, let's take a quick look at the main components of the mechanism: the "worm" gear (the spiral-shaped section that connects to the handle/button) and the pinion gear (the round part that turns the string post). Nearly all guitar tuners operate on this same mechanism, with extremely few exceptions, most notably Ned Steinberger's linear-drive "gearless" tuners and Bill Rickard's recent and very innovative design involving a cycloidal drive system.

Many vintage guitars, and the modern instruments that emulate them, will have open-back or exposed-gear tuners. As the name suggests, these tuners give an unrestricted view of the worm-and-pinion arrangement. This also means that these gears are susceptible to collecting dust, case lint, and any other particles or fluff that may happen to come along. If debris builds up in the gear teeth, it can cause sticky and unreliable tuning and potentially even gear failure. For this reason, I generally use a dry lubricant on open-back tuners, rather than a paste grease or other sticky lubricant that could gather contaminants. I've had moderate success with powdered graphite, but lately I use Tri-Flow for open-back tuners, on the advice of the great repairman and tuner connoisseur Frank Ford. Although this dispenses as a liquid oil, it works primarily as a carrier for microparticulate PTFE (aka Teflon), which adheres to the gear surfaces and continues acting as a lubricant even after the oil itself has dried.

When lubricating open-back tuners, I generally remove the strings, which allows me to turn the tuner freely in both directions. I apply a small drop to the point of contact between worm and pinion, and then use a string winder to turn the tuner fairly quickly. After about a 1/3 turn of the pinion gear (usually three to five turns of the handle), I apply another drop at the same contact point and repeat again after another four or five turns. Then, I turn continuously to move the pinion gear through another complete rotation. This generally leaves a nice, even layer of lubricant around the perimeter of the gear, without making too much of a mess. Keep a cotton swab on hand for any stray drops of oil that drip out.

Modern cast-body or sealed tuners are a different story. In the past, inexpensive tuners were known for low quality metal and poor manufacturing tolerances, and were frequently to blame for unstable tuning. Companies such as Grover, Schaller, and Gotoh addressed this by offering tuner upgrades with better gears, tighter tolerances, and fully enclosed bodies, which allowed the gears to turn in a bath of thick paste grease. These tuners were designed to be permanently closed, and in many cases they still perform admirably after decades of maintenance-free service. However, the small disc or plate that seals the back cover can fall out and be lost, exposing the gears within, and allowing the grease to collect contaminants.

In these cases, I will disassemble and clean the tuner as best I can. A heated ultrasonic cleaner is the preferred tool for this in my shop, but a simpler solution is a brief dip in boiling water followed by a scrub with an old toothbrush. Next comes reassembly and relubrication with a midweight grease. Blue or blue-green lithium-based greases generally work well for this, and those with added PTFE are even better, but even basic white lithium grease from the hardware store will usually be fine. I don't overpack the gearboxes—just a reasonable dollop is sufficient. Then, replace the back medallion to enclose the gearset again. If you cannot replace the medallion, consider the dry-style lubrication approach instead (as detailed for open-back tuners) using Tri-Flo.

The third common family of tuners uses a stamped sheet-metal back which covers the worm and pinion. Among the brands that produced these, the best known was Kluson, whose tuners were found on Fender guitars for decades, as well as on many acoustics. These tuners often have a small hole in the back plate, which is meant to allow lubrication at the strategic point where the worm and pinion intersect. This hole can also let in a surprising amount of dust/grime, as I've discovered in some cases when I disassembled older sets. If the tuner feels a tiny bit gritty or tight, a drop of oil through the hole should be sufficient. If it feels worse than that, I usually do a thorough disassembly and cleaning.

Since we're discussing tuner maintenance, I'll also mention another very common issue that comes up with vintage tuners: rotten or cracked plastic buttons. Many vintage tuners suffer from this issue, and I've handled a number of guitars whose buttons simply cracked off when turned. This is due to long-term degradation of the plastic used for the buttons. There is no real practical fix for this other than replacing the buttons. Most supply houses, such as StewMac, sell melt-on buttons meant for this purpose. After the tuner shaft has been cleaned of all old plastic and oxidation, the tech can heat it up using a flame or soldering iron (I prefer the iron, as the flame can sometimes leave a black deposit) and press the button into place, molding the plastic around the shaft of the tuner. When everything cools, the button is solidly together.

One last note: Most tuners have a bushing (metal sleeve) that installs in the face of the guitar's headpiece to support the string post. This simply presses into place on older tuners. On newer cast-body tuners, the bushing is threaded and screws through the headpiece into the tuner housing. The press-in ones are notorious for falling out at inconvenient moments when changing strings, and can disappear under tables or into crevices very easily. (Trust me on that one!)

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When working on your guitar, make sure the bushings are a tight fit, or else put a plastic bag over the headpiece so any lost parts will get safely caught. It's also a good idea to check the bushings on modern tuners periodically—they are very often loose, and sometimes the washers beneath them can cause mysterious rattles and buzzes that are maddening to diagnose. Don't crank them too hard as it can cause problems in the surrounding finish. Simply snug them up with an open-end wrench or socket. Nearly every cast tuner around uses a 10mm wrench. When lubricating tuners, especially older open-back models with press-fit bushings, I also put a tiny drop of oil between the string post and bushing, at the 6 o'clock location where the bushing is closest to the nut.

Got a Question?
Uncertain about guitar care and maintenance? The ins-and-outs of guitar building? Or another topic related to your gear? Ask Acoustic Guitar's repair expert Martin Keith by sending an email titled "Repair Expert" to Editors.AG@stringletter.com and we'll forward it to Keith. If AG selects your question for publication, you'll receive a complimentary copy of AG's Acoustic Guitar Owner's Manual.