Coordinating dual truss rod adjustments

[tomhug]

1) Can the relative tightness of each dual truss be inferred from how far the truss rod nut is protruding into the truss rod cavity?



When I use a notched straight-edge to assess the relief it does seem like the amount of back-bow is greater on the treble side than on the bass side. (Hard to see from the pictures, but you can tell from rocking the straight-edge)







2) Is there a procedure to "reset to default"? In other words make sure the truss rods are appropriately synched with each other.

I have never actually adjusted the truss rods on this bass, and the neck seems very stable, but it does seem like the relief this bass had the last time I measured it is no longer there.

This bass normally wears light-gauge D'Addario Chromes (ECB81) Bass Guitar Strings which are 45-65-80-100, and has been outfitted with these gauge strings for at least the past 5 years.

My target set-up is basically standard Fender specs. i.e. Not super-low action.

[JimmyJ]

Those coupling nuts (technical name, I think) should be tightening against a metal plate (see pic below) and basically doing the same thing on other end where the plate is hidden under the nut area.  They don't actually move up or down as you tighten or loosen them, unless the rods are completely loose.

So picture 2 long metal rods running from the nut to this point and threaded for the last few inches.  Their job is to counteract the pull of the strings and help keep the fingerboard relatively flat.  This push and pull is effected by weather because the wood expands and contracts a bit.  So when it's hot and humid out you may need to loosen the truss rods and when it's cold and dry you may need to tighten them.  Or maybe it's the other way around, I can't remember.

I think the point is to have relatively the same amount of torque on both rods and adjust them together as the need arises.  There is no "reset to default" but since you have the strings off you could loosen them until the nuts are free, and then go from there.  I would suggest putting at least a few tightening turns on them before bringing the strings up to tension.

When I make adjustments I do it with the strings on and tuned up.  If I feel like there's a bit too much relief I'll tighten them a 1/4 turn or so, physically pull the neck back and forth to be sure things are seated, and then retune and see how it feels. 


Hope that helps.
Jimmy J

[edwardofhuncote]

This past year I went on The Great Flatwound String Tour and had to totally readjust my Alembics to the wildly varying string tensions between Pyramid Golds, D'Addario Chromes, and Thomastik-Infeld Jazz Flats.

The extreme-case OCD in me wasn't going to settle for just backing off, or tightening up a 1/4 turn on each, without remembering 100% sure what the last adjustment was. So, I just backed both nuts all the way off to slack and started from zero for every new brand of string I tried. I think the Pyramids had the most turns, then the D'As. The T-I's are dang-near slack on my fretless Alembics.

Jimmy J. is right on, and I'm nuts though... just tighten or loosen the truss rods evenly an 1/8 to 1/4 turn at a time. I wouldn't go any more than that in a day, unless my bass was rattling and it was soundcheck or something.

*FWIW- higher humidity tends to decrease relief, meaning you'd most likely need to loosen the rods. Lower humidity, tends to cause relief, meaning the rods would need to be tightened. I have found that in the cold, dry months of Winter, simply keeping a humidifier box in the case with each of my basses is sufficient to keep from having to make any truss rod adjustments at all. Especially the Alembics... those laminated necks really help with stability.

[rv_bass]

Greg, what humidifier boxes do you use for your cases?  I need to get some for mine (old cast iron radiators suck the moisture out of everything!). Last year I tried a clay core one, but I don’t think it helped much.

[tomhug]

Those coupling nuts (technical name, I think) should be tightening against a metal plate (see pic below) and basically doing the same thing on other end where the plate is hidden under the nut area.  They don't actually move up or down as you tighten or loosen them, unless the rods are completely loose.

So picture 2 long metal rods running from the nut to this point and threaded for the last few inches.  Their job is to counteract the pull of the strings and help keep the fingerboard relatively flat.  This push and pull is effected by weather because the wood expands and contracts a bit.  So when it's hot and humid out you may need to loosen the truss rods and when it's cold and dry you may need to tighten them.  Or maybe it's the other way around, I can't remember.

I think the point is to have relatively the same amount of torque on both rods and adjust them together as the need arises.  There is no "reset to default" but since you have the strings off you could loosen them until the nuts are free, and then go from there.  I would suggest putting at least a few tightening turns on them before bringing the strings up to tension.

When I make adjustments I do it with the strings on and tuned up.  If I feel like there's a bit too much relief I'll tighten them a 1/4 turn or so, physically pull the neck back and forth to be sure things are seated, and then retune and see how it feels. 


Hope that helps.
Jimmy J

Thanks, Jimmy - that is very helpful.

I discovered some curious things:



I don't have a plate, I have two separate truss rods. This might be due to the fact that mine is a '77 and among some of the earliest dual-truss Series I's (I know they made singles after mine, and began offering dual-rods before it, but not all that many.

Another curious thing is that only one of these (the bass side) has a washer.


Neither truss rod had much tension on it. On the treble side I could twist it with my fingers after a very modest 1/8 turn of the wrench. On the bass side, there was about a 1/4 turn of tension loaded onto the rod - the one with the washer. As I mentioned, I've never adjusted the truss on this bass, and until now never needed to - it seemed to always bear the correct amount of relief - even after switching from Roto 66s to Chromes several years ago. A testimonial to Alembic Build Quality, laminate necks, and getting lucky with the wood on this particular neck (I suppose).

So this raises some questions (to Mica, or anyone who might know):

1) For a 1977 Series, should I have a washer on both rods? I assume so.
2) Does anyone know what size that washer is? As you can see from the pic, mine is behind my LED wire, and won't seem to come off the rod without potentially damaging the LED wire. Looks like .41 inches circumference (using a digital calipers). I can't get to the aperture or tell how thick it is, though.

[edwardofhuncote]

Nothing special, very low-tech Rob... just some plastic snack boxes with sponges. All mine are in cases with guitars now. I knew it'd be a while before I could get to them again. 


*found an incidental picture of one, in the case with my Persuader. It's that purple box against the back. I just leave them in all year, and wet them in the Fall when it starts to get cold/dry.

[edwardofhuncote]

I wonder if it might have had a washer on the tandem rod too, that just went missing sometime along the way Tom... especially since yours seems to have a nice sturdy neck beam. It may have worked loose and fell out long ago. I can't see where it would hurt to have one there. 

[rv_bass]

Thanks, Greg, I'll try your method with the snack boxes, small holes in the lid, and most sponge inside.

Tom,  here is a photo of the truss rods in 77-744, both have washers.  The cut in the wood in yours is a bit odd, the maple block that holds the truss rod extends over the Purpleheart margin, and the nuts are two different sytles. I wonder if your truss rod without a washer is a replacement.

[tomhug]

Thanks, Greg, I'll try your method with the snack boxes, small holes in the lid, and most sponge inside.

Tom,  here is a photo of the truss rods in 77-744, both have washers.  The cut in the wood in yours is a bit odd, and the nuts are two different sytles. I wonder if your truss rod without a washer is a replacement.

Wow - Thanks for the detailed pic of your '77 - I really appreciate it. Our basses are 38 builds apart, mine is 77-706.

In my pic, the nuts do look different, but they've just aged differently. I've taken them off and polished them up with some gorgomyte, they look quite identical now. I'd be surprised if the rod was a replacement - I'm the second owner and Mica provided a pretty detailed prehistory for this bass. It did have LED's and a refinish in 1981. I've owned it since 1986, and the only major work (aka the treatment) I had done by Ron & Company back at the mother-ship.

[JimmyJ]

Hey Tom,

Yeah, always interesting to see some of the handwork details on our instruments.  Let me remind you that the main thing about the system that you're concentrating on is "function".  And it sounds like you have a solid neck which requires very little in the way of truss rod tension.  So that's a GREAT thing and I urge you to try not to obsess over this interior detail not looking quite right, if you know what I mean.

That said, it does seem like there would normally be a metal washer there for that nut to seat on.  Hard to tell from your pic but I wonder if the routing on that side is flat enough to fit the washer?  If not, that could have led to the decision to purposely leave it off rather than having it not sit squarely against the wood.  Just a random thought. 

If you want to pursue it, pull off that low-side washer, bring it to the hardware store, and buy TWO of the closest you can find to that size.  Install them both and balance those truss rod nuts. 

Then perhaps make a transparent truss rod cover and install an LED light source to show off the inner workings.  (I'm only teasing!!  I understand and respect those who are into this kind of detail.  For me, it's more about function than form.)

Jimmy J

[tomhug]

Hey Tom,

Yeah, always interesting to see some of the handwork details on our instruments.  Let me remind you that the main thing about the system that you're concentrating on is "function".  And it sounds like you have a solid neck which requires very little in the way of truss rod tension.  So that's a GREAT thing and I urge you to try not to obsess over this interior detail not looking quite right, if you know what I mean.

That said, it does seem like there would normally be a metal washer there for that nut to seat on.  Hard to tell from your pic but I wonder if the routing on that side is flat enough to fit the washer?  If not, that could have led to the decision to purposely leave it off rather than having it not sit squarely against the wood.  Just a random thought. 

If you want to pursue it, pull off that low-side washer, bring it to the hardware store, and buy TWO of the closest you can find to that size.  Install them both and balance those truss rod nuts. 

Then perhaps make a transparent truss rod cover and install an LED light source to show off the inner workings.  (I'm only teasing!!  I understand and respect those who are into this kind of detail.  For me, it's more about function than form.)

Jimmy J

Hi Jimmy,

That is sage advice and I am firmly in the "if it works, don't fix it" camp. The only reason I started down this road was that I found I suddenly had a bit of a back bow, which this bass has never had. It turns out the back-bow was from measuring with the strings off. I put the old set of strings on and the relief I am accustomed to seeing is back.

I'm not sure i can pull off that bass side washer without risking the LED wire, so I may just leave it. It also turns out that the truss rods themselves are slightly uneven in terms of how far they protrude into the truss rod cavity. I've basically put everything back the way it was, tightening them based more on the original feel from when I loosened them in the first place rather than by their appearance. You may also be correct in that the routing in the cavity might not allow a washer to lie flat. I need to find better light and my glasses... I'll look at it when I have daylight tomorrow.

All things being equal, I would slightly prefer to have washers on both sides, since compressing the wood on the treble side might start a process that would be difficult to repair later. However, the more important fact is that this bass has been dead-solid-perfect for the 32 years she's been in my care. The reason I started looking into this stuff is I am back to using this Series I 4-string as my primary player, so I was doing an annual fingerboard oiling, fret-buffing, cleaning, etc. New strings and strobe-tuning will be next, as soon as I get the truss rods sorted (whatever that winds up meaning).

Thank you so much for weighing in here with your experience. I really appreciate it!

Tom

[soflbass]

I'm no expert on Dual truss rod adjustments. However, mechanically it would make sense that as long as the relief on the high and low sides of the neck were within a thousandth of an inch of each other with a particular string set, that would be ideal. Dual trusses allow for more fine tuning than single truss rods and provide more mechanical strength. As an example, my Essence truss rods have the same symptom as your bass; the high side is looser torque wise than the low side. But my relief on the high and low sides is almost identical. As long as the relief remains close to the same, there will be no chance of neck twist, if that is your concern. Since wood is not a homogeneous material, variations will occur on individual basses.

[lbpesq]

Tom, rather than measuring relief across the wood, you really want to see the relief across the top of the frets.  Hold the string down at the first fret and where the neck leaves the body.  It may be helpful to use a capo or a friend to hold the string down at the first fret.  Then, when you hold it down near the body, the string creates a straight edge across the top of the frets.  Check your relief in the middle of the string.  How much relief?  A good place to start is that there should be just enough room to slide a pick into the space for a snug fit.  I usually start on the bass side (low E on a guitar), then adjust the treble side in the same manner.  You should be holding the instrument vertically, like you play it, when checking the action, not lying on its back.  Gravity will make a difference.  Don't worry about whether the dual rods look like they've been adjusted the same.  It doesn't matter.  Just so long as the neck has the relief you prefer on both sides.  Don't be scared.  It's just a long metal rod with a nut on one end.  No voodoo involved.  The most common mistake people make is adjusting too agressively.  A little adjustment can go along way.  You should be turning the truss rod nut 1/8 - 1/4 turn at a time, no more.  Give it some time to settle in after each adjustment, ideally a day or two, to fine tune it.  And if you want to add a washer to the side missing one, go ahead, no big deal.  There is no "standard factory default setting".  It's  like the mirrors in your car.  Made to be adjusted to an individual's needs.

Bill, tgo

[tomhug]

The happy ending:

I did source a washer for the other truss rod. I've got new strings on now, and I'm waiting for the neck to settle to see if any further relief adjustment is required.

I generally follow the guidance from Joey's setups tips, and/or the Fender site, and/or this very useful eBook when doing my own setups.

Answering my own question from my first post: "1) Can the relative tightness of each dual truss be inferred from how far the truss rod nut is protruding into the truss rod cavity?" In my case, no. The truss rods actually terminate at slightly different lengths, so the appearance is meaningless. As many wise folks here advised, it's the feel and the effect on the relief on the neck that should be the key indicator. I guess the reason I asked the question in the first place was concern that someone prior to me had adjusted the rods drastically unevenly. Since I've had the nuts off of the rods several times to measure and assess the situation, I know that, for lack of a better term, they've been reset to "default". But I dialed in the level of tension on each rod based on how they felt when I took them off, not how they looked.

Thank you to everyone who jumped in with advice and guidance!