Does my bolt on neck need shims?

Discussion in 'Hardware, Setup & Repair [BG]' started by gapupten, Feb 20, 2005.

  1. gapupten


    Dec 29, 2004
    I can't seem to figure any other solution.
    I bought a used bass and it seems it has a problem.
    My saddles are down as far as they can go. My trust rod has been tightened to the point that the strings are buzzing on the upper frets, and still the action is way too high on the lower part of the strings.
    It would seem that something needs to lift the middle of the bass. Are shims the only answer?
    Has anyone done this?
    Am I missing something basic?
  2. Figjam


    Aug 5, 2003
    Boston, MA
    Seems to me that is when a shim is needed.
  3. Yes, I think a shim is needed.
    First, you've pulled a backbow in your neck with the truss. That's why you're buzzing at the low frets. Did the same thing trying to dial in an action on a cheaper bass, and I ended up using a shim.

    Before you do anything else, release that tension on the neck a bit. If it's backbowed now, it will be really bad when you take the tension off the strings. Use the Gary Willis procedure to adjust the amount of relief in the neck. Don't worry about string height right now. Just get the relief set.

    De-string and remove the neck carefully. Some necks fit extremely tight in the pocket. You would not want to crack some of the thin wood around the pocket trying to force the neck off if it does not come easily. If it's tight, rock it gently out of the pocket lengthwise, not side to side.
    Shims: When it comes to this, you'll need some very thin. I actually used a piece of aluminum soda can (cut to size with scissors). It's very thin.
    You'll want to size the shim to fit about the last 1/2" of the neck, closest to the bridge. I punched 2 holes in my shim to fit over the two neck screws.
    Bolt the neck back on, taking care to snug up (don't overtighten!) the screws closest to the shim first. Then snug up the others. Finally go back over all the screws and make sure they are tight.
    Restring. You'll have to raise your saddles.
    Check the neck relief again. If it's still in the ballpark, try adjusting your saddles to get the action playable in the lower frets. Check your upper frets. Action should be lower and alot more playable.
    If not, you know you need a thicker shim. If action is too low at the higher frets, or you run out of saddle adjustment, you need a thinner shim.

    Good luck, and let us know how it goes.

  4. gapupten


    Dec 29, 2004
    Thanks for the information. I really appreciate the good folks here who take the time and share their knowledge. It will take a week to get back to it, I will let you know how it turns out. :)
  5. This solution may not be the answer to this problem, depending on what is meant by upper frets, lower part of the strings etc.

    If you are pulling the neck back, and still have too high an action at the 5 fret, while the strings buzz at the 20 fret, then surely you need to pull the neck back more, to reduce the curve, and raise the bridge height to clear the neck end frets.

    You could also investigate whether the nut needs to be adjusted, or its grooves made deeper.
  6. I agree with Mottle at this point.
    Perhaps the neck has been adjusted too far in the wrong direction and the nut should be looked at.
    Of course a better explanation could lead to better answers.
  7. gapupten


    Dec 29, 2004
    At present, I am buzzing at the 2nd thru 6th fret and the action is too high on the 10th thru about the 15th frets and rediculously high from the 16th to 21st fret. Also, the saddles are as low as they will go.
    Sorry I did not paint a very good picture previously.
    Do you agree that with this picture, shimming the neck is in order?
  8. Gosh, I am so wrong here! I misread the original post, thinking backwards. I thought he had high action at the upper frets/low action on the lower frets.
    Thanks for stepping in. If gapupten had followed my advice, he would have really messed up. I apologize..

    I would still check the neck relief and see what it shows. Does the neck look bowed forward? I'm thinking that it probably is. It definately does not have backbow.

  9. gapupten


    Dec 29, 2004
    I think Magento's assumption about my facts were correct.
    Sorry for the bad input. Speaking directly to Mottlefeeders assumptions..If I am pulling the neck back, I have fret buzz on the 5th fret and too high action at the 20th fret. In other words, the top of the neck and the saddles are as far down as they can go, but I have a big gap between the strings and the 20th fret.
    If everyone assumes that facts the way that Magento did, I assume everyone would agree that I need to add shims in the neck pocket to lift the middle.
    Any final thoughts before I go looking for an aluminum can to cut up?

    Thanks for everyone's help.
    gapupten: You might have missed my recent post. I misread your first post. Don't go to the trouble of shimming the neck until you get the neck bow (relief) dialed in FIRST. If you don't, after adding the shim your bass still won't be setup properly.
    Here's a quick and dirty test:
    Tune the bass to proper pitch. Hold the first fret of a string down(or use a guitar capo to hold it down) and then hold the same string down past the fretboard on the body. This creates a straight line on the string. You can use your elbow to press the strings down past the neck. Check the clearance at the 8th fret between the bottom of the string and that fret. There should be a little clearance, about a credit card's thickness is ok. If there is none, you need to loosen the truss a bit (about 1/8th turn). If there is more, you'll need to tighten the truss some.
    Always loosen your strings when tightening the truss. You don't want the truss pulling against the tension of the strings.
    Always bring the strings back up to proper tune. You got to get that tension back on the neck to know if your adjustment is enough.
    Remember: This relief isn't dependant upon saddle height. The neck has to have it, whether you want a low or high action. Once you have this set right, you'll only have to make small adjustments to this from time to time.
    Once you get this dialed in, try to adjust your saddles to get the best action without fret buzz. Then you'll know if a shim is in order, and you can go that route. If the upper fret action is still high, you'd probably do well with a shim. It sure worked for me.
    If you have any questions, please ask.

  11. gapupten


    Dec 29, 2004
    Mag, I believe you got it right the first time. I have gone through getting the proper relief in the neck, credit card thickness at the 8th fret routine. So I am convinced the relief is correct. When I pull back on the neck (tighten the truss rod further) the reduced bow brings my strings in contact with the 2nd thru sixth fret. After that is done, I have a large amount of clearance (more than a half inch) between the 21sr fret and the bottom of the string. And that is when my saddles are at the bottom. If I raised the saddles, the gap would widen even more.
    So from yours and other postings, I am convinced I need to add shims to the neck pocket to raise the heal of the neck up. I have seen other postings discussing the use of cut strips from an aluminum can as shim material. What did you use for shim material? Did it work well?
  12. I think the shim will help you. Some bolt-on necked basses used to come with a screw on the joining plate that allowed you to jack the neck's angle a bit. I think the shim is better, because it allows more contact between neck and pocket compared to tightening against that little adjustment screw.
    The cheap Rogue bass I worked on not only played much better, but sounded better too.

    I used aluminum from a soda can because I needed something really thin, I didn't want to use something like paper or plastic (would probably kill sustain), the aluminum is readily available and is easy to cut to shape, and I didn't have to run out looking for expensive shim stock when I wasn't really sure of the thickness that I needed.
    That aluminum changed the action dramatically. A very thin shim goes A LONG WAY.
    Good luck, and looking forward to hearing of your results.

  13. gapupten


    Dec 29, 2004
    After numerous posts discussing my situation I decided that a neck shim really was required for my newly acquired used bass.
    So after cutting up my aluminum diet mist can (good can for a shim), I unscrewed the screws holding the neck in place and lo and behold what do I see but a piece of thin plastic, another neck shim already here. But apparently not enough. So I added my aluminum strip to the plastic, closed it up and after a half-hour of setting tension on the neck, raising saddles etc, I decided that was not enough either, but definately moving in the right direction. So I opened it back up again, this time folded the aluminum in half, and moved it towards the back of the pocket. After another half hour of screwing around with neck tension, saddlehights etc, I can now play this bad boy. :hyper:
    So I plug her in, and find out one of the pots is shot. :crying: Weak scratchy ouput from the passive Bartolini P pup in a PJ lconfiguation. My $399 investment in a Pedulla Series II is looking weak right now. :bawl: Next weekend will be pot replacement weekend.
    But thanks guys for the help with the neck shim... Everyones comments really helped me understand the process. And I think that part of the job is done. :hyper:
  14. I have a suggestion.. Replace that plastic shim with more layers of aluminum or other non-rusting metal. Why? Even though aluminum is quite soft, it's not as soft as that plastic, and that could hurt sustain. The neck and pocket need to have a tight joint on bolt-on necks, and that plastic could actually act as a dampening piece. That's why I decided to use aluminum instead. I had tried plastic too, but decided against it.
    If I was gonna put money into something like this, I'd consider thin brass shimstock, or even some stainless or something that wouldn't rust.
    I'm surprised at the amount of shim that is needed to correct the angle problem. Man, somebody goofed when they set that up originally.
    I'm happy to hear that it's gonna work for you.

  15. Do you get a thinner tone if you use a diet can?
  16. Those shims sound extreme to me too, seems like there should be a less-shimmed option (but whatever works). A perfectly flat neck will be a problem too, you want a slight curve. I alway adjust tension with the strings on and tuned and wait 15 mintues between adjustments.

    Tossing a couple new pots in a 400 pedulla does not sound like you got a bad deal even with all the neck stuff.
  17. gapupten


    Dec 29, 2004
    So now I get it. I should have used a regular soda cans and then I would not have had to use so many shims. It is all clear now. :p ;)
  18. gapupten


    Dec 29, 2004
    Since I am new to neck shimming, I figure I have some more work to do to get it right. At this point, I am happy that it seems that I am messing around with the right things.

    As to the pots, its just that I did not expect to be messing around with something else.
    But I am having fun learning so much new stuff, ...NOT. :scowl:
  19. I have been following this thread because I have recently bought a s/hand Warwick fretless that looked as if it would need to be shimmed, and this evening, I tried aluminum (Kronenbourg 1664 if you must know :) ).

    With one shim, I seemed to have lost some of the tone, and with two, I was sure that I had a thinner tone, and it didn't sound as 'fretless' either.

    I had some oak edging strip from a previous woodworking project, so I heated it, scraped the glue off, and used that as a shim (the wood, not the glue). It sounded so much better.

    Yes, I know that it is subjective, and that a difference in shim height will initially change the height of the strings above the pickups, but I am convinced. Any luthiers care to comment?
  20. Mottlefeeder: Your test was very interesting. I have no doubt that different shim materials could produce a difference in tone. Using a shim of any kind would probably do this.

    One thing that puzzles me is the fact that some basses used to come with a micro-tilt adjustment screw at the backplate. There was another plate inside the neck pocket, and this screw was adjusted against that plate to get the proper neck angle, then the neck bolts were tightened. In this case, only the tilt screw would be making contact in the pocket, instead of the entire neck butt solidly joined. I would think this would really hurt sustain. After all, isn't that the main reason for neck-thru-body construction? Sustain?
    I would think the shim (even aluminum) would be a better option than the tilt screw. At least in the latter case, one would have more neck making contact with the pocket.
    I guess experimentation would be in order..