Trying to Straighten American Fender Neck

Discussion in 'Hardware, Setup & Repair [BG]' started by DavePlaysBass, Jan 21, 2018.

  1. DavePlaysBass


    Mar 31, 2004
    I just came across a Fender P Bass that was left too long with a forward bow and the rod is maxed out or so I think. It's a 2008 American P bass. I took the neck off and removed the truss rod nut that is at the heel. It is not a 10-32 as I had expected. It would only thread on an M5 stud at Lowes and it seemed a little wobbly with the M5. Interestingly enough it takes a 3/16" Allen wrench while having an apparent M5 thread on the other end.

    I grabbed some M5 lock washers and M4 regular washers. The M5 washers would not fit over the truss rod. I drilled out the thinner regular M4 washers with a series of 3 drill bits (3/16", 13/64", 7/32"). This took a while to figure out. This was awkward. I held the washer with a lineman's plier while drilling towards the floor into a wood block. After getting three successfully drilled out, I put two washers on the rod and clamped up the neck.

    I used a 5" C Clamp on my "card table" with a 2x4 underneath the neck and 1x4 blocks on the 2nd and 17th fret (see pic below). With the nut loosened, I put the C clamp exactly in the middle which is around the 7th fret. I applied pressure on the C clamp. This is where I got a little nervous. How far do you go? Is a little at a time better? Is the 7th fret or the middle the place to apply the pressure. After I applied the C clamp pressure I tighten the rod as far as I was comfortable going.

    Does all this sound legit?

    I have never removed a truss rod nut before. I was very surprised at how loose it is when reapplying until you get to the last turn or so. Does that mean the nut rotation is only effecting back bow over that 1 turn? I am struggling to see the physics of how the washers help anything and when the nut rotation actually starts doing something to the neck.

    Original Setup

    Higher Backbow Setup - 5/32" from 2nd fret, 6/32" from 15th fret (stamp of approval from Mr Kitty)

    Attached Files:

    Last edited: Jan 27, 2018
  2. sissy kathy

    sissy kathy Back to Bass-ics Gold Supporting Member

    Apr 21, 2014
    Arbutus, MD
    Okay, now flip that clamp upside down so the screw handle is out of the way and wrap the neck in a heat pad set on medium for about a week. Take the pad off and let the wood cool for at least 24 hours before unclamping it. The goal is to have a straight neck once the wood is cooled and unclamped. The washers do two things, they help in preventing compression of the wood where the nut makes contact, and they move the nut out from the end of the threads giving you a little more adjustment. you want the vast majority of the nut engaging the threads all the time, remember there is quite a bit of tension on those threads
    Last edited: Jan 21, 2018
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  3. James Collins

    James Collins

    Mar 25, 2017
    I can't tell if you have something preventing the clamp from indenting the back of the neck... Metal on wood is bad.

    Next, when I saw someone do this, it was on the StewMac channel, and I believe he went for neutral.

    Also, I still do not believe you can hurt a guitar neck with a truss rod unless that guitar neck was going to unhealthy to begin with.

  4. 96tbird

    96tbird PLEASE STAND BY

    You asked about the physics of the washers giving more adjustment. The rod is in a curved slot. When you force backbow, the slot straightens and the rod straightens, the FLAT distance between its ends is longer. the rod being anchored at one end is pushed out of the hole on the threaded end. So, what if there are no extra threads left and this only pushed more unthreaded rod out? the threads don’t go into the neck past the wood bearing surface? The nut will dead end at the end of the threads without contacting the bearing surface. You have zero threads left. You need to add a spacer to move the bearing surface further out so it covers the threads. Let’s say you space out to five threads covered by the spacer. You now have five revolutions of the nut until you’re out of room.

    As for how far should you clamp the neck, don’t be afraid. You can bring it all the way down to touch the table and it will be fine unless there’s a bad defect grown into the tree it came from. But there is no need to go that far. Deflect it an inch. Tighten the nut. Unclamp it and check it if you have back bow. Rinse repeat. Heat treat if needed.

    Edit out spellcheck crap.
    Last edited: Jan 22, 2018
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  5. DavePlaysBass


    Mar 31, 2004
    Thanks. I am going to avoid heat for now. But I did flip the clamp around in order to get more contact area on the neck. I am hoping that two washers, lighter gauge strings, and some patience with the clamping gets me there. I will keep my mind open to heat if things don't pan out.

    I am using sticky weather stripping on the clamp as it makes contact with the neck and also on the wood blocks on the ends. I have a ton of it left over from a pickup installation.

    I get it. Thanks for that detailed explanation. Basically when we tighten the nut, we make the truss rod pull straight.

    As for progress. I have unclamped it twice now and each time the neck was basically straight with the truss rod maxed out (no back bow yet). I have been somewhat hesitant to clamp it too much. The good news is the neck definitely responds with a forward bow when I loosen the truss rod. However, it seems there is a small range of usable rotation.

    So I now have more back bow clamped into than before. I am measuring the center to be about 3/16" below the nut side and about 5/32" below the neck pocket side. We'll give it another day and see what she looks like tomorrow.
    Last edited: Jan 24, 2018
  6. 96tbird

    96tbird PLEASE STAND BY

    Definitely needs a spacer washer so you can get more threads to tighten it. Get one or two in there.
  7. DavePlaysBass


    Mar 31, 2004
    Presently I have added two M4 washers that are drilled out to 7/32".
  8. Lownote38


    Aug 8, 2013
    Nashville, TN
    When I've clamped necks in the past, I've always done it without the truss rod nut tightened (or even off completely). That way all the tension is on the neck via the clamp and not from the truss rod nut.
    sissy kathy likes this.
  9. DavePlaysBass


    Mar 31, 2004
    In my situation I believe the clamp is doing most of the work given when I release the clamp the neck with tightened rod does release some of the back bow. I am guessing it is not a dig difference whether the truss rod or the clamp is moving the wood when trying to add back bow back into the neck. Also I would assume that you would want to tighten the truss rod before releasing it from the clamped position (with loose rod).
    Last edited: Jan 24, 2018
  10. Killed_by_Death

    Killed_by_Death Snaggletooth Inactive

    If you don't heat it, won't it just snap right back to how it was before you started?

    Only snug the truss rod nut before you put strings on it, and then make the final adjustment after it's at pitch.
    Lownote38 likes this.
  11. DavePlaysBass


    Mar 31, 2004
    The truss rod can greatly benefit from external assistance (such as a clamp) when tightening as well discussed in many forums and threads. The truss rod should not be expected to move the much larger wood structure particularly if the neck has been permitted into excessive forward bow territory. I think you should tighten the truss rod nut while clamped and then loosen the nut to desired relief when installed on the bass with strings at tension. In this case you are not asking the truss rod to move the neck.

    Will the clamping hold or will it just deflect back? From what I have read it depends on the wood, the amount of forward bow being corrected for, the time the neck has been bowed, the time the wood is clamped, and the final setup requirements (relief specs, string gauge, etc). In my particular case the initial forward bow is not too extreme. I have added washers which essentially increases the truss rod back bow force. And I plan to use a lighter gauge string.
    Last edited: Jan 24, 2018
    96tbird likes this.
  12. Killed_by_Death

    Killed_by_Death Snaggletooth Inactive

    Adding washers should not increase forward bow, but they should allow you more threads on the truss rod for the nut to tighten the neck into a backward bow.
    Lownote38 and sissy kathy like this.
  13. DavePlaysBass


    Mar 31, 2004
    I agree. I got my forward bows backward. Corrected
    Killed_by_Death likes this.
  14. 96tbird

    96tbird PLEASE STAND BY

    Right: tighten the nut while clamped in backbow and once strung loosen it to proper relief. If you do not tighten it, you’ve missed the entire point of trying this before moving on to other remedies. If it will hold back bow once you snug the nut up, you’re golden. Heat shouldn’t be needed.

    Now if the neck has back bow and won’t go into relief (opposite situation) you’d clamp it into fore bow add heat and hope.
  15. DavePlaysBass


    Mar 31, 2004
    Making progress. The neck has held 40-100 strings at pitch at a constant usable relief for 3 days. Only problem is I am getting more buzz on the E and A than I would like from the 3rd to 7th fret with 0.015" to 0.020" of relief at the 9th. I am going to try a set of 45-105s and see if I can get lower action without buzzes. As I transition to the thicker strings I am going to put it back under the back bow clamp for a day and add an additional washer or two. Not sure its needed but I would like to stick a fork in it and not have to return here in the future.
  16. Bruce Johnson

    Bruce Johnson Gold Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    A technical note about adding washers under the nut of a truss rod:

    The only reason to add washers is if the nut has run out of threads on the rod. That is, if you can feel the nut lock up and you can feel a spring-back of the the rod twisting. In that case, back the nut off and add a washer or two. This spaces the nut back and gives it another two or three turns of thread ahead of it.

    And for reference, the reason why Fender-style truss rods run out of threads sometimes, is because the rod has previously been overtightened. One or both ends have crushed into the wood, making the threaded end stick out farther than it should. And so the nut runs out of threads and jams up at the last thread.

    Don't add washers unnecessarily if you haven't run out of threads. That spaces the nut back and reduces the number of threads engaged inside the nut, which weakens it and makes it more likely to strip.

    Adding washers does not increase the strength of the rod, or the amount of force that it is capable of applying to the neck.
    Lownote38 likes this.

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