Eastman Truss Rod Question

[George Henry]

I have encountered several Eastman mandolins with which I been unable to adjust the neck to adequate straightness. In other words, the nut bottoms out. Is it that the rod is installed incorrectly? Or is it something I have failed to do? Mandolins with this issue have included a MD-505, a MD-905, a MD-315. Yes, I have adjusted a lot, having been employed as set up tech by dealers and by a manufacturer.

Any help with this issue would be appreciated.

[Parker135]

Is there space to add a washer under the nut?

[George Henry]

Ran across another Eastman today with same. An old Eastman dealer friend of mine suggests a "design flaw".

[rcc56]

Saturday, I worked on a small-shop banjo that had a truss rod that was just about frozen. The instrument wasn't more than a year or two old.
Maybe it was caused by glue on the mechanism . . . [???]
If it ever needs major adjustment, it will have to go back to the maker under warranty.

[HoGo]

I wonder why these rods don't work? What did they do wrong?
Are the threads too short or the nut is locked by rust or something?
I prefer using threaded rods for my truss rods and brass nuts so these two problems won't occur.

[Richard500]

If the OP means by ‘bottomed out’ that the nut is at the end of the threaded portion, then washers are definitely the solution.
If ‘bottomed out’ means that there’s more thread but the nut becomes resistant to tightening, and the neck can’t deflect at all, then the rod is either positioned too high or is locked in its groove (by glue or corrosion, say). Adrian’s use of threaded rod, IMHO, could invite the second problem, but only if he was sloppy with glue, which I sincerely doubt.
If I suspected a ‘stuck’ rod, I’d probably lock two nuts together so the rod could be torqued in both directions to loosen it. Bit by bit.

[HoGo]

If the OP means by ‘bottomed out’ that the nut is at the end of the threaded portion, then washers are definitely the solution.
If ‘bottomed out’ means that there’s more thread but the nut becomes resistant to tightening, and the neck can’t deflect at all, then the rod is either positioned too high or is locked in its groove (by glue or corrosion, say). Adrian’s use of threaded rod, IMHO, could invite the second problem, but only if he was sloppy with glue, which I sincerely doubt.
If I suspected a ‘stuck’ rod, I’d probably lock two nuts together so the rod could be torqued in both directions to loosen it. Bit by bit.

I use heat shrink tubing all along the truss rod except the parts that are exposed. I try not to get glue on the rod even though it wouldn't stick to that.

[George Henry]

On one of these adjustment resistant Eastmans (which I owned at the time), I turned the nut past its limit. I heard a snap! Turns out the rod did not break, but the brass nut stripped. So I found a stainless steel nut of the same thread, used one or two extra washers, and tightened to a "safe" limit (nothing broke). I got it somewhat straighter, at least straight enough to rush over to GC and sell it to them.

[Glassweb]

Design flaw indeed. Just about every Eastman we sold from our store had this problem. Too bad, because these are otherwise very good mandolins for the money.

Get it together Eastman... fix the truss rod issues. And how about a new, more user-friendly tailpiece design while you're at it....

[Peter Kurtze]

Is this issue specific to recent examples, or older, or both?

[George Henry]

I owned a newer MDA-815 mandola. When I attempted adjusting, it reached its thread limit and I stopped. The neck was not perfectly straight, but functionally straight enough. I have traded off that mandola. The other aforementioned models were earlier ones.

[Richard500]

[QUOTE=Glassweb;1808925]Design flaw indeed. Just about every Eastman we sold from our store had this problem. Too bad, because these are otherwise very good mandolins for the money.

So which is it- too short threaded length, or weak nuts?

[George Henry]

I don't know for sure, never having disassembled an Eastman neck, but I wonder if the rod has enough curve, with a filler piece glued on top, to make the neck straighten when the nut is tightened. If the rod is essentially straight when installed, tightening the nut will have little impact.

[ProfChris]

I'm working on a 1930s Gibson tenor guitar which I bought for my own use - it has a single action truss rod with a brass nut.

I asked around before I began adjusting, and was told:

1. The wood under the washer can compress over time, so adding one or more washers is a sensible move to avoid bottoming out.

2. The brass nut can hold position, but tightening it can strip threads. The solution is to clamp the neck towards a back bow to reduce tension on the rod, and then tighten the nut. This is simple - a block over the lowest frets and the neck joint, a beam on top of that, and then a clamp in the middle of the neck to curve the neck towards the beam.

Following this advice, I was able to get the neck straight without excessive force on the nut. String tension has pulled it back into more relief than I want, so I plan to repeat the process to readjust. The best technique seems to be to put more back bow into the neck than needed, and then slacken off to get the correct relief once the strings are on.

[HoGo]

Vintage Gibsons of 20's had trussrod nuts of copper/ brass plated steel. Perhaps that was your case too.

[Tom Haywood]

FWIW, adding a second washer can cause vibration noises that are hard to locate. Two things to watch out for. Adding a thin, soft material between the washers may solve one vibration. Also, the lower screw on the truss rod cover may contact the washer, so cutting some length off the screw may be required.

Compression of the wood can sometimes be dealt with by using a larger washer and cutting it's edges to fit in the truss rod slot.

[George Henry]

My two mandolins are a 1920 Gibson A-4 and a 1929 Martin Style 20. Neither have adjustable truss rods. Both are dead straight. Which is better? No truss rods with straight necks or non functional truss rods on crooked necks?

[rcc56]

Many years ago I visited Jean Horner, who built a lot of mandolins during the 1980's and 90's.
He had two that were just about finished, one varnished and the other lacquered.
I commented that the instruments had no truss rod. His response, "Why do you need one on a mandolin?"

Jean also built banjos, and he did always install truss rods on them.

I suppose their is justification for a truss rod on long necked mandolins with thin, narrow profiles that might be set up with heavy strings; at least from some points of view. But in many ways, an adjustable rod reduces the structural integrity of the neck, and the rigidity becomes dependent on the operating mechanism rather than on the wood itself. That's fine when the mechanism performs as intended, but many times they do not. And the current common practice of burying the adjusting nut deep into a large pocket in the head increases the possibility of a peghead break if the instrument receives a shock. Those pockets should be made as small and shallow as possible. I would like to see more exploration with solid reinforcements made of hardwood, carbon fiber, or solid metal.

I know that pre-truss rod Gibsons generally do fine as long as they are not abused, neglected, exposed to too much heat, or strung too heavily. My absolute maximum for them is 11-15-25-40, although I tend to prefer 10 1/2-14-24-38 or 40. I will note that those old Gibson's do have reinforced necks, but the reinforcement is a triangular piece of maple.

[HoGo]

One shuld keep in mind that thickness of the neck is big factor. Pre-trussrod Gibsond had quite chunky shorter necks (the ovals) with hard maple core that made more than 60% of the neck shaft and glued together with strong hide glue. These do hold well under normal circumstances. But once you don't watch humidity or temperature you don't know what will happen...
Many modern makers use longer necks and thinner profiles, sometimes much thinner. They also use softer varieties of maple. I only handled handful of Eastmans and they were among thinnest necks I've seen on mandolins and used either one of the chinese maples or red maple which are not as hard as US hard maple.
I wouldn't say the trussrods reduce structural integrity of neck. If you forget to install it then yes, but PROPERLY installed rod IS PART of the neck and makes it stronger AND adjustable. I emphasise the word properly because many modern manufacturers (mostly china, but also some smaller makers) don't understand the exact role of the rod. They just churn out "product" and when buyers prefer having a screw of some sort in the neck they often just add it without thinking much about it and the workers have no idea at all about it's function.
The weakening of the headstock end is not part of the original design - the nut pocket in headstock of old Gibsons is way up high on the headstock above the thinnest part of the neck. Someone screwed the design few decades ago and many manufacturers followed the suit of placing the nut right below thw nut. I'm talking about single compression TR here.
Perhaps it was Leo Fender with his patent of "reverse curve" truss rod in his guitars. His reasoning of why it works is probably wrong (tightened rod wants to straighten and takes neck with...- were this true, the original Gibson rod should work in opposite direction which it does not...), but he needed the nut just below fingerboard surface to be accessible. Luckily he buried the central part of rod deeper and that's what makes them work on the thin long necks. I've seen many strat copies with truss rods barely working because someone decided to bury it just below fingerboard surface and often fingerboard being maple the neutral axis of the neck was just about at the rod depth rendering the rod nearly useless. And many more followed this in countless other styles of instruments....

[Richard500]

I realize this is dangerous territory having followed the discussion here for only a year, but has anyone gone into temperature compensation issues. That is, having the rod precisely compensate for the strings?
This popped up because I recently remembered an inquiry about Mars hardware I received at work.

[George Henry]

So it seems that the conclusion to my original post is that the design or installation of the Eastman truss rods is not optimum. Is there any practical.method of repairing these truss rods?

[Parker135]

Have you tried adding a washer under the nut?

[Nick Gellie]

George

I own two Eastmans and I have adjusted the truss rod to straighten the neck. Both truss rods worked. So the question is how old is your Eastman? If it is something fairly common Then why not shoot Eastman an email pointing out the problem and ask them to test the manufacturing processes for mandolins. You never know it might improve the truss rod design.

[George Henry]

Well, I found a very slightly used MD-305 with a very straight neck and snatched it. I now have a beater and/or HS graduation gift for a grandchild.