Shimming is an appropriate method of altering the action. It is unadvisable to put it between the heel and the tension band. It should sit between the top of the heel above the lag bolt and the rim. I do a lot of banjo repairs etc here and use thin wood veneer for shims. Sometimes I need to glue two or more pieces together then trim them to size so they are hidden by the heel shape.

Wayne’s right. I’ve had a shim there on my player for probably 56 years now. No problems. It’s stable and still doing what it’s supposed to.

banjonz I completely believe you. Could you explain further why it's unadvisable to put the shim between the heel and tension band?

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Originally posted by tomd7

I can certainly take the neck off and put a shim around the top lag bolt where it connects to the tone ring if needed. . . . I'm curious as to whether moving the shim down to the lag bolt really necessary.

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If you are going to shim to lower action, the upper lag area is the correct place for the shim. 

I have shimmed necks in both locations to raise or lower action. It's not without issues. While it avoids distorting the rim as happens when using the co-rods to adjust action, I believe it distorts the lag bolts. They get pulled/bent into a new alignment. But I think they'll survive.

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Originally posted by tomd7

banjonz I completely believe you. Could you explain further why it's unadvisable to put the shim between the heel and tension band?

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There should be a gap between the end of the neck and the tension hoop. The hoop needs to be free to move up and down to play its part in adjusting head tension.

I believe the tension hoop is isolated from the pot and does not play a role in the transfer of vibrations that creates a banjo's sound. If transfer of vibrations throughout the instrument is even what's happening. So doing something that not only eliminates the gap but increases the pressure of the neck on the tension hoop strikes me as bad for the sound. It's also bad for freedom of the tension hoop, as I just said.

It's also bad for the overall structure of the banjo, I think. The neck needs to make solid contact with the pot at the two lag bolt locations. Shimming at the tension hoop changes the geometry in a way that weakens the connection at the upper lag. (I believe)

Here's Warren Yates describing why there should be a gap between the neck and tension hoop.

Roger Siminoff is perhaps the best known person I can think of who advocates for the neck touching the tension hoop. He knows more than I do, but I still disagree. I choose to believe Warren.

There are two ways I see that this would hurt the tone. The first has been mentioned, which is that it creates a lot of pressure on the tension hoop.

The other, much bigger factor here is that it prevents the heel from contacting the skirt of the tone ring. A lot of the tone of a well setup-up banjo comes from vibration between the neck, tone ring, and rim. In my experience, without this contact the tone ring vibrates unnecessarily long and with too many high overtones. In addition, the banjo is less loud and doesn't play with as much authority in the core of each note.

You'd be better off using a shim at the heel contact and then a lower bridge to further bring down the action, imo.

Shimming the hoop puts pressure on the upper tone ring edge. Unless you are looking to dampen the sound, shim at the lag where a solid connection is desired.

Thank you everyone these are the kind of detailed answers that I love about this site. I’m getting a piece of mahogany today for a shim at the lag bolt.

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Originally posted by tomd7

banjonz I completely believe you. Could you explain further why it's unadvisable to put the shim between the heel and tension band?

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All you'd want is an, as stiff as possible, connection between both ends of the strings.

Anything that introduces any 'spring action' into this chain will dampen your banjo's response (tone, sustain).

The tension hoop is not a stiff part of the pot, but has a spring suspension by means of the head.

The fretboard has been glued to the neck. When relying only on the contact spot between fretboard and (the already springy) tension hoop you're doubling the resilience in that area, robbing your banjo's response even further.

You wouldn't believe what difference a .015 gap between fretboard and tensionhoop made to my banjo, tried as a last resort in bringing out its full potential. (look for 'Warren Yates' and 'Cumberland Gap').

It turned out my banjo, for years, had the upper lag bolt contact point not bearing the load it should have.

For setting up the action properly, there's nothing like a heel reset/cut. But for trying out, of course, a shim at the upper lag bolt will be more than good enough...

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Originally posted by tomd7

banjonz I completely believe you. Could you explain further why it's unadvisable to put the shim between the heel and tension band?

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I can't really give you a logical explanation except that I feel the fretboard should not bear up against the tension band. I have read postings from folk who say that the pressure of the band against the neck affects tone. I am uncertain of this. Another reason is if/when you change the head, the shim falls out. This may not be an issue, However, having the shim 'locked' into position by the neck being tightened against the rim I feel is the best. Just my 2c worth.

The simplest reason I can think of for not having contact at the tension hoop, and especially not shimming at that point to adjust action, is that it creates three points of contact between the neck and pot and that's one too many for setting neck angle. If the tension hoop shim successfully lowers the action, then one of the other two contact points is probably doing nothing. That's not good.

Hey all, I wanted to report back on my experience. You're absolutely right. I made a mahogany shim this weekend and put it on the upper lag bolt so it sat flush on the tone ring. Put everything together, with the gap between the tension hoop and fingerboard. My banjo sounded amazing! The tingy overtones that I was trying to get rid of where gone. It really sounded good.

Got to work this morning and found that that the lower lag bolt had pulled out of the wood from the stress of tightening the upper lag bolt. I'm not surprised, my dad said it had pulled out long ago and he'd sorta fixed it but it wasn't that solid. So.... I'll be fixing that and then putting it back together. But I'm really excited with how it did sound for that short bit of playing it with the properly done shim. I appreciate everyone's advice.

I recommend drilling the pulled out hole clean and gluing in a well-fitted plug of the same wood as the neck and redrilling a new lag hole.

Decades ago I started using a thin maple shim on my banjo, and not knowing any better, it touched the tension hoop. I was told that shimming was preferable to using the coordinator rods which "could" push the rim slightly out of round which might pinch the tone ring fit.

I first put the maple shim a bit lower in height than the surface of the fingerboard rather than have the shim appearing too "obvious".

When I got my next banjo and conversion neck, the neck builder asked me what height bridge I preferred and he cut the neck angle with that bridge height in mind, and no shim was needed. Another decade later, with more banjos added to the mix, I decided to try the real high 3/4" Snuffy Smith bridges just to see what would happen, and I had to use maple shims again. It was from BHO I learned about the shim touching the tension hoop pinching the tension hoop, which could hamper head "tuning" and perhaps even head changing. Like Roseann Roseannadanna used to say "it's always something!" I cut back my bridge heights to no more than 11/16" and I don't seem to need shims any more.

The latest banjo I had to shim was an original RB 500 from 1967 with terrible high action! I purchased some little brass shim stock, and in disassembling the banjo to get at the neck heel, I found one of the lag bolts was LOOSE and backed right of the heel when I tried to tighten the coord rod! Yikes! I put a couple of long wood splinters in the heel and plenty of wood glue and it went back together very solid. I fit two thickness of my brass shim stock into the area just above the upper lag screw where it would bear on the rim and tone ring. This worked VERY WELL. Sounds great and is stable.

I just ordered a conversion neck from Eric Sullivan and told him I wanted the neck heel cut for an 11/16" bridge.

If you're ordering a conversion neck, be sure to advise what bridge height you prefer and a good neck maker will the cut the heel angle accordingly.

I also learned by the way, that one reason 1960s Vega bluegrass banjos were sonically handicapped was by the rounded neck heel fit that you would "rock" a bit with those three screws around the lower lag bolt. Poor sonic contact of the neck heel to the rim. Some folks even had the factory original neck heels re-cut for snug fit.

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Originally posted by steve davis

I recommend drilling the pulled out hole clean and gluing in a well-fitted plug of the same wood as the neck and redrilling a new lag hole.

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I agree. The replacedment wood plug should be larger than the hole for the lagbolt to give the screw thread something to bite onto rather than intersecting the hole and glue joint. Just my 2c worth.

When Jimmy Cox built a my tb-2 conversion neck he suggested I have him cut it for an 11/16 bridge because of my big hands.
I said "yes",but have gone to a .650 favorite bridge height for great low action.

Another thing about shims.
Shimming at the tension hoop can give a false impression of associated hook/nut head tension adjustments.

steve davis and banjonz What size dowel do you recommend for a plug? I've seen 1/4 inch and 5/16 inch mentioned on the forums, in either maple or hickory. I'd like to know what's worked for you.

I get better luck drilling a bigger hole and installing a bigger Maple dowel instead of using the same size hole.

Good choice on Mahogany shim.

Lots of people use the .023 credit card which is paper.


I have cut Bamboo shims with horizontal grain instead of vertical grain. ??