neck relief problem on 73 fender PB

[cedric verglas]

HI guys,

I have a 1973 precision bass guitar at the shop with a strange problem on the neck.
it comes for a bumps at about the 4th fret that makes it impossible to play in the lower positions. I've tried to play a bit with the trusrod without succes, the bump still be there on the 4th fret. I took my sloted rule to check the straightness of the fingerboard and bump appered on it of about 1mm (a bit less in fact). I deceided to unfret and make a fingerboard leveling with aluminium raduissed (6") bloc and 80 then 150 grit sandpaper. The finger board was dead flat at this moment. I freted it and started my fret leveling setup to perfection. When stringing it, every thing was good with a 2.4 mm on low E and 2mm on G and no buzz. but for only 3 hours. The bump came back !! a bit less than before and I can't fix it with the trussrod.

any ideas would be welcome.

[Bob Gramann]

Has the fingerboard come unglued from the neck under the 4th fret? Or, is there another break in the neighborhood?

[cedric verglas]

It doesn't seem so. But when I get it, the rosewood fingerboard was already thin (2mm max on the edges) and most of the frets were touching the maple. When I removed the frets, I could see on each sides and all the way long a bit of maple on the fret slot assuming that someone else have made a leveling previously for the same problem.
the finger board is pretty dry and easily fall apart when unfretting.

[Michael Lewis]

A hump appears at the 4th fret? And after leveling? Something is not right. Tap on the fingerboard and listen for any change in "note" from the impact. The handle of a screwdriver is a good tool for this. You are looking for a solid sharp response all along the whole board. Carefully listen for any changes in the 'click' response. This procedure is looking for any loose sections of the fingerboard. Tap the board, not the frets. Tapping the frets is another process looking for loose frets.

Also look very closely for any cracks or checks in the neck, especially around the 4th fret area. That hump is coming from somewhere.

[Mark Wybierala]

Very odd. Nothing better in a brawl than a Fender neck and a PB is about as big as they get. The elevation is across the entire fretboard??? Does the trussrod function? I would do the tap thing suggested but loosen the trussrod nut first -- remove the nut entirely so it doesn't create a misleading rattle. You can also clamp the heel in a vise and just do a bit of flexing of the neck via the headstock to see if anything odd is happening. This is a pretty stout piece of maple so you can apply some muscle.

[Barry Daniels]

A string compensation jig may be necessary to fix a problem like this. The jig places the neck under simulated string tension while the frets are leveled.

[cedric verglas]

thanks guys for your support.

I don't have yet stewmac neck jig but I still have made 50 refret/fingerboard leveling with succes without it. I've found no special sound change on the fingerboard tapping it. there's no crack I can see with my eyes the maple neck piece is not what we call now AAA grade but something between a A and B. the IRW fingerboard seems brittle.
Trussrod works in this way: under string tension, when the TR is loose there's a big bow. when I check frets level with a fret rocker it's quite good every where. when I tighten the TR the bow flatten gently and fret's check is still good. but when I tighten it a bit more to achive a good setup, the hump (bump) come back and the fret rocker statrs to rock around the 4th when i check frets #3/4/5. the deal is that it good when I check #1/2/3, #2/3/4 and #5/6/7 and upper, with a little somthing by checking #4/5/6. Never saw that. when checking the fingerboard with a notched straightedge I see the same thing, a gentle curve between 4th and 20th frets and a kind of back bow between 1st and 4th frets.
Frets are OK, fingerboard sucks! But I'ts a collector instrument! what about making a new fingerboard? and if it's the neck wood itself???....

I am a bit lost.
I am a bit lost

[Barry Daniels]

It most likely is the neck wood. I had a bass neck with a crook in the grain that would cause a hump and twist when the strings were brought up to pitch. The string tension compensation jig was the ONLY way to remedy that instrument.

[cedric verglas]

you mean by that this jig put your neck on tension without string in the same way if it was strung, that's it? so I can see the wood deformation.
I assume that I'll make it 'cause 400 bucks it a bit too much actually. i'll have a look to DIY neck jig on the web.
Do you think I need to unfret or a good fret job with that kind of jig will do the job?

[Barry Daniels]

Yes, that is the way it works. You don't have to pull the frets if there is sufficient fret height that a little surfacing can remove the hump without taking the frets too low.

I have a short cut solution to the jig. Let me take some photos this afternoon and I will upload them. You can make a basic jig with parts you probably have laying around.

[cedric verglas]

much thanks barry!

here it's 10pm already and I leave the shop...I'll see it tomorrow.

[Mark Wybierala]

Looking forward to seeing another version of the neck jig process. There are many options if you just take a good look at the Stewmac concept. Something can be just cobbled together that is very simple for Fender necks alone using only scrap. The bolt pattern for guitars and bass necks is the same and you can use the same plank (body simulator) for both guitars and basses. To fully simulate a bass use a bass bridge and for a tele or a strat use a cheap hard-tail guitar bridge. All you need to do is get the elevations right for the bridges sitting on spacers.

So what are we thinking here? How is a trussrod significantly elevating the 3rd fret under string tension? ...very odd?

[Michael Lewis]

Apparently the neck is too flexible in that area. Since the truss rod pulls this shape into the neck I wonder about the position of the truss rod in the neck. Might check for even/ uneven depth by running a strong magnet along the back of the neck. The closer the magnet is to the steel rod the stronger it pulls.

[Barry Daniels]

Here are a couple of photos of my basic jig. This is a version that holds an LP style straight tenon neck that is off the guitar. I have other versions for other style of necks. The one for acoustic necks has a small platform that the heel sets on.

The jig is just a couple of supports and a midway bracket that is screwed into a threaded insert. The bracket is made from 0.012" thick spring steel so it is thin enough to not get sanded during fret leveling.

[Barry Daniels]

Here is a close up of the bracket. The way the jig works is similar to the Teeter jig. In use, I snug up the 1/4-20 threaded bracket and then turn it another 3/4 rotation. That comes close to giving the neck tension equal to six strings. You want the truss rod to be set to where it will be in use. Then level the frets.

[Jason Rodgers]

... snug up the 1/4-20 threaded bracket and then turn it another 3/4 rotation. That comes close to giving the neck tension equal to six strings.

I'm going to trust that you know how your own jig works, but if someone wanted to replicate this setup, how do you know the tension is similar or equal to string tension? Do you put a straightedge on the strung-up neck and measure the relief before setting it up in this jig? That seems like a factor that will be essential for Cedric to hunt down this funny little bump.

[Barry Daniels]

Of course I use a straight edge! The 3/4 rotation came from using the jig numerous times and I just threw it out there as an aid. If one has the time and the tools, straight edges and dial calipers can be used to get precisely the amount of deflection as the string tension creates. I just found that the jig works about as well if you don't get all number bunched up.

[Mark Wybierala]

I'm concerned that a neck jig may not duplicate the very odd situation that the PB neck is exhibiting. I'm thinking that a large part of the distortion is being caused by string pull.

To simplify, one of my routine processes with bolt-on necks is to simply adjust the relief on a guitar to zero using the existing old strings. I remove the neck and place it in my stewmac guitar vice with the neoprene jaws at the heel -- quite tight. I have a turnbuckle headstock support and I forcefully elevate the headstock and using my straightedge, I adjust the relief to zero again using the turnbuckle headstock support. This is how I inspect a neck for level frets. In the zero relief position, I can then manipulate the trussrod to find the optimum setting for leveling the frets while preserving fret-meat. The end result of this process is quite good with I believe about 95% or more of the guitars leaving the shop as superior playing guitars. The jaws hold the neck quite well and my vise is hard-mounted to 2" of sugar maple. (The neoprene jaws are quite up to the task of keeping the heel in a permanent position and I've rechecked the accuracy after letting a neck sit in place over a weekend.) This works well with a healthy quality neck with a uniform strength along its length which is usually the case especially with Fender neck construction and no scarf joints along the length. Using the turnbuckle to elevate the headstock in a way, simulates string tension but not in a fully accurate manner. It only duplicates the headstock deflection of the string pull. It doesn't accurately put the force in the same vector. If you did this setup and acquired the hump in the process I'd be comfortable that you were going to be able to address the needs of the neck. But if the hump did not appear, you'd need to employ another strategy.

Here's another perspective. Just minimize the defect rather than attempt to cure it. The instrument has solid value as a collector piece. The neck is what it is. Just bring down the height of the offending frets to compensate but short of creating a visually obvious issue. If you get too deep into this, you run the risk of harming the vintage value. Not all vintage instruments are going to be great instruments. I feel a sense of sadness and partial failure when this is the case but that is just the reality. Set it up the best you can and move on.

[Barry Daniels]

Mark, your technique is interesting and it proves that there is more than one way to manipulate a neck. Mine is simple but it works too. One won't know what is needed on the subject at hand, until they try it.

[cedric verglas]

Thanks guys,

I followed Mark advice to minimize the defect working around the 4th & 5th frets and I now have a pretty good setup for a 73 PB.

I'll make some of those neck jigs because it seems really practicle and fast.