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Acoustic bass repair help (top lifting)

Discussion in 'Hardware, Setup & Repair [BG]' started by no1likesme, Jul 22, 2009.

  1. no1likesme


    Dec 26, 2006
    Shepherd, MI
    So, the top and bridge on my abg are starting to lift up a bit from string tension. The bridge and top go back to their normal position when the strings are removed. I am guessing that this is caused by a failed glue joint between the top and some bracing.

    It would probably cost more than the bass is worth to get it repaired by a luthier, so I am gonna have to fix it myself.

    What would be the best way to go about a repair?

    I have a pretty good selection of hand tools.
  2. 202dy

    202dy Supporting Member

    Sep 26, 2006
    The best way to go about the repair is to determine what is causing the problem.

    Here are some questions you need to answer.

    How big is the hump in the top?
    Can the action be adjusted to accommodate the hump?
    Is the bridge lifting from the top?
    Is there a brace(s) loose or from the top?
    Is there a cracked brace?
    What is the top material? Plywood? Solid? What species?
    Is the bridge plate (pad) loose?
    What material is the bridge plate made from?

    You'll need a mirror and a good strong light to collect this information. Bridge plate problems are easier to diagnose by feel with thin (.005") feeler gauge material.

    None of these problems are easy to fix. Some are more technical than others.

    Post the data here and someone will help you.

    Good luck.
  3. Pilgrim

    Pilgrim Supporting Member

    I would suggest having a luthier at least look at it and estimate a repair. You might be surprised. But if it's too much....

    1) Buy Dan Erlewine's book on guitar repair and read it thoroughly. It will be extremely valuable to you.

    2) Read 202dy's post and answer questions....some of which may be best guesses on your part.

    3) Buy any specialized tools required...I suspect you may need some Stew-Mac tools for this (and they ain't cheep) and you may end up comparing their cost with the luthier's services.

    4) After integrating the info you have gathered, do the repair.
  4. Craig_S

    Craig_S Inactive

    Oct 15, 2008
    Metro Detroit
    By the time you buy the proper tools for the repair, you will be better off taking it to a qualified repair person.
  5. Jazzdogg

    Jazzdogg Less barking, more wagging!

    Jul 29, 2006
    San Diego, CA
    You might want to switch to a low-tension string and see if that helps.
  6. ByF


    May 19, 2009
    202dy has a pretty complete list of questions and suggestions, but I have one more:

    Is the bridge actually separating from the top, or is the top just bowing up so the back of the bridge is higher than before?

    If the bridge is still firmly attached, it doesn't affect the playability, and you can't find anything broken, you might want to leave it alone. Some "belly" in the top is normal, even in fine guitars. If nothing is broken, there may not be anything that can be done.

  7. no1likesme


    Dec 26, 2006
    Shepherd, MI
    the bridge is still attached to the body, there is no visible gap between the bridge and top even when it is "lifting up". The bass still sounds and plays great, although the action is a little higher than it was before (obviously).

    Would the amount of "belly" change with temerature/humidity? I ask because I first noticed the issue a few weeks ago when it first started to get hot outside.
  8. ByF


    May 19, 2009
    Craig_S, I must respectfully disagree with your opinion. The OP says he already has a good selection of hand tools, and that's about 90% of what you need for guitar repair.

    And even if he buys a tool for the job, he probably won't throw it away after the job is done--he'll keep it and use it again. Maybe he'll do a job for someone else, and make some money.

    And anyhow, what is a "qualified" guitar repair person? Does your state have a Board of Guitar Repair Person Certifications? Most people who build and repair guitars learn how by doing it, and by asking other people how to do it. That's what the OP is doing--he'll learn how, and then he'll be as "qualified" as anybody on TB. The next time someone asks this question, he'll be able to tell us all how it's done.

    I happen to find working on musical instruments to be fun, and it's fun talking to other people about it. Where's the fun in taking the job to someone and paying them to do something I can with my own hands?

  9. Low Main

    Low Main Supporting Member

    Nov 27, 2004
    One solution I like is to add a tailpiece and have the strings continue to pass over the saddle slots of the existing bridge.

    The tailpiece takes the string tension that's distorting the top and moves it down to the tail end of the body.

    The other nice thing it does is, if you have an under saddle piezo element, you relax the immediate downward pressure on the piezo and get a nicer amplified sound. But the pickup signal strength goes down too, so you have to turn up a bit.
  10. ByF


    May 19, 2009
    I don't know; that's a good question--I live in a very dry climate, so I don't deal with humidity very much. Is this the first summer this bass has been through?

    It might be worth while to do an inspection inside, even if you don't suspect anything is broken. Just for peace of mind, you know.

  11. RustyAxe


    Jul 8, 2008
    What many fail to realize is that so-called flat-top guitars aren't flat. There is supposed to be some "belly". A straight edge put across the lower bout should rock a bit, with the high point in the center. When a guitar dries out from low humidity the belly disappears, or becomes concave, if severe.

    JLD makes a product called the "bridge doctor" that compensates for the effect of high tension on a bridge. Some Breedlove guitars are actually designed to use it, allowing for a lighter bracing of the top. It's easy enough to install, and has "saved" some guitars from needing more expensive work.

    I agree with those who recommend a visit to a good luthier for an assessment and estimate. You may find that there's nothing wrong at all!
  12. Craig_S

    Craig_S Inactive

    Oct 15, 2008
    Metro Detroit
    Then he should get to purchasing a few of these:

    Oh, and a couple good books, as well.

    You, honestly, need to ask what a qualified repair person is?? :eyebrow:

    Let's start with someone who has a reputation for performing quality work; not some hack down the street who thinks he can handle the job, because he was able to install a faucet once. :rolleyes:

    It's also quite possible that, when someone asks about this sort of repair in the future, the OP will be able to tell that person why they shouldn't do it the way he did it. Don't you think?

    Years ago, when I apprenticed with a reputable, local repair man, I saw enough do it yourself nightmares to make me change my opinion of the average "do it yourselfer's" abilities.

    Working on musical instruments can be fun. Screwing one up, is definitely not fun.
  13. Captain_Arrrg


    Jan 23, 2008
    Mountains of Colorado
    Endorsing Artist: Spector Basses
    It not unusual to have to readjust your action when the seasons change. You may want to consider a humidifier for the dry months so it doesn't weaken over time due to humidity changes.

    Did you ever consider that since you were working in a repair shop, you would naturally see allot of the failures? Why would the competently maintained instruments have ended up that establishment?

    The last sentence is QFT.
  14. ByF


    May 19, 2009
    I agree--clamps are very useful in acoustic guitar repair. Repair books are great, too. I have a few, and the local library has some very good ones, which I have used.

    But as of his last post, the OP hadn't even looked inside the bass to see if anything was wrong. He didn't even know if he had a problem, and was asking for advice. He was interested in fixing it himself (if needed), and he got some advice on how to evaluate the problem.

    If you heard a knocking under the hood of your car, would you immediately have it towed to the nearest qualified auto repair person, or would you lift the hood and see if it was something you could easily fix yourself? It might be a squirrel jumping around under there! :D

    My attitude is this: if someone comes to a "Hardware, Setup and Repair" forum asking for advice, it's right to offer him the best advice we can. I don't see the point of telling someone to take it to a "professional" before we've even found out whether or not he really has a problem. I see that all the time here; someone comes and ask how to adjust their action, and someone will tell them to take it to a "professional" for a "real" set-up. I think that is doing the person a disservice.

    Anyhow, it's the OP's bass and his money, so he gets to choose.:)

    And good night,

  15. Craig_S

    Craig_S Inactive

    Oct 15, 2008
    Metro Detroit
    Yes. It wasn't just that I was seeing them, it was the amount I was seeing. My favorite, to this day, is the attempt at a fret replacement, using a hacksaw to widen the fret slots and super glue to hold the frets in place. Not that CA glue is never used to hold frets.

    The OP came for opinions, I gave mine. You are correct. It's his choice.

    Good night,

  16. no1likesme


    Dec 26, 2006
    Shepherd, MI
    I didn't mean to start any conflicts here, Taking this bass to a professional is not a realistic solution for me, as I am unemployed and this bass only cost me $150. I do have a lot of experience with woodworking, and have built a few solid body instruments. However, I am rather new to the whole acoustic thing and I was just asking some opinions before I went and tore my bass apart.

    to completely recap my experience with this instrument: I have had it for about a year, This being the first summer that I have owned it. When I purchased it (used) it did not have a noticeable "belly" and it stayed that way until summer started and I noticed a slight bulge under the bridge. The belly has not increased noticeably in the last month, and the bass still sounds and plays great. I am simply concerned that this may lead to a more severe issue that will possibly render my bass unplayable, and I would like to repair it if necessary.

    Thanks for the help

  17. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    you should be able to take it to that professional and bug him for a couple minutes of his time to suggest the best way to fix it. (no more than that, please, time is money)

    he may just tell you that a little bulge is normal and not to worry about it.

    if not, knowing woodworking is good, and building solidbodies is good, but to reinforce craig S's point, i'd usually rather fix a guitar that had been dragged behind a bus on a rope than one that had endured "home repair".

    you only get one chance to glue it up right, so study hard and get all the tools to get it right the first time.
  18. Hi Ron.

    While a competent instrument builder or a luthier may be the best person to help OP, from the start he said that the instrument in question "is probably not worth it".

    I for one appreciate that attitude and seeing now that it's a $150 instrument more or less, I for one feel that it's a justified attitude.

    Without knowing the exact brand, the price tells something. To me at least.

    Plywood top, liberate bracing, budget construction.

    IMLE, plywood tops tend to move more, because the bracing is usually inadequate to support the top on climate changes. If it was braced proprly, the sound would become dull and uneven. Other reason is the direction and species of the plys, sometimes they form a "bi-metal" strip.

    As the bridge is not lifting and the bass sounds right, I'd do nothing. Loose bracing in budget instruments (IMLE again), usually develope into an audible nightmare rather quickly.

    When eyeing the top from the bridge to the end of the FB, how concave is it?

    If it's reatively flat, I'd say there's no problem.

    When tapping the "belly" with Your knuckles (damping the strings of course ;)), does it produce a sound, like something was loose? Rattles, buzzes?

    If not, just enjoy Your bass.

  19. 202dy

    202dy Supporting Member

    Sep 26, 2006

    Actually, that is the third question in the list.

    It is notable that there has been no data posted in this thread to date. That makes the giving of specific advice risky at best and foolhardy at worst. It also makes debate on any topic at any level moot.
  20. ByF


    May 19, 2009
    Oops, you're right. Sorry 'bout that.