Misterious reverse shimming on a mustang bass, what should I do?

Fabio_MIJ

Fabio_MIJ

Feb 3, 2016
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#1
Hi everyone,

I have recently bought a 2nd-hand mustang bass from a local shop.
I have noticed that the neck pocket was shimmed with a thin metal plate so I am making a check during cleaning session. Look at the photos here, it is a partial reverse shim, the job doesn't look top notch.

I guess it does not come like that from the factory, the reason must be to increase the neck angle to solve an action problem, what do you suggest me to do? keep it like that? take it out or replace? At the moment the bass does not have any stability or dead-spot problems,

I will post other photos when the work is finished, the model is pretty nice and unusual: 3T sunburst pawn shop model with one middle-position humbucker replaced by a Dimarzio model one! Tons of low-end power.

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Best!
Fabio
 
#2
While a shim at the body end of the neck is more common its not unheard of to need a shim at the other side, I’ve had to do it a couple of times myself. It could be factory. I don’t know what they cram in there now for shims, especially the overseas instruments. As far as what to do, you could take it out and try to set the bass up and, if you have issues, put it back in. The other option is to leave it in and see how it sets up. Kinda 50/50 on that.
 
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#3
Matt Liebenau said:
While a shim at the body end of the neck is more common its not unheard of to need a shim at the other side, I’ve had to do it a couple of times myself. It could be factory. I don’t know what they cram in there now for shims, especially the overseas instruments. As far as what to do, you could take it out and try to set the bass up and, if you have issues, put it back in. The other option is to leave it in and see how it sets up. Kinda 50/50 on that.
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Thank you for your advice! The bass is mexican.
 
#6
At a guess you would shim the front of the neck pocket if you arrived at a situation where you had to jack the saddles impossibly high to get the action high enough to be nicely playable.

It might happen if you stick the neck from one bass onto the body of another, mixing models or manufacturers.

Oddly I owned two PJ Mustangs for a while, and swapped their necks over from time to time. The necks definitely belonged to the bodies, and it was hard to get any semblance of decent action when I swapped them over. The older neck was rosewood and the newer was pau ferro.
 
#7
At a guess you would shim the front of the neck pocket if you arrived at a situation where you had to jack the saddles impossibly high to get the action high enough to be nicely playable.

It might happen if you stick the neck from one bass onto the body of another, mixing models or manufacturers.

Oddly I owned two PJ Mustangs for a while, and swapped their necks over from time to time. The necks definitely belonged to the bodies, and it was hard to get any semblance of decent action when I swapped them over. The older neck was rosewood and the newer was pau ferro.
 
#10
scottfeldstein said:
I dunno. I think I would take it out and do a full setup. If that shim is needed, you'll find out why. If it's not, then at least you're smarter than the person who put it in in the first place.
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That appears a little backwards to me.

I'd assume someone wouldn't have shimmed the neck just for the fun of it and start out by seeing how it works with it attached, then remove it if it turned out to make things odd.
 
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#11
JohnArnson said:
That appears a little backwards to me.

I'd assume someone wouldn't have shimmed the neck just for the fun of it and start out by seeing how it works with it attached, then remove it if it turned out to make things odd.
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That could actually be a point, cause the harmonics are completely out of tune, so it needs in any case a complete setup. The shim was also badly placed, with a border bent by one of the screws :rollno:.
I'll set it up completely and check out if the shim is needed.
 
#12
JohnArnson said:
That appears a little backwards to me.

I'd assume someone wouldn't have shimmed the neck just for the fun of it and start out by seeing how it works with it attached, then remove it if it turned out to make things odd.
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You're a trusting soul. I assume that work done on the instrument in the past was done by an incompetent boob. But perhaps not. Could be I've watched too many Dave's World of Fun Stuff videos.
 
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#16
byacey said:
I think most of the problems are due to discrepancies in the neck pocket route. Why they would be so different on factory instruments made with the same template and router, I can't even begin to guess.
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factory or not it's cheesy.

likely from changing out the tool bit and not qualifying its length/taking the tool's offset or there were debris under the body and the neck pocket area got raised up and undercut. the operator just threw in a body and hit cycle start and made scrap.
 
#17
I've seen a lot of weird back shimming like this on basses with a ski jump. Bad techs and bad "do it yourself" people do this and think it will help. It doesn't! Hopefully this isn't the case with your bass. I've never seen a Fender factory shim like that, though, so I don't think it was in there new.
 
#18
Back again, I set up the instrument. I removed the shim, cleaned the fretboard, fixed the pickup to the body, and setup action and harmonics.
The bridge saddles are a bit to the endpoint for both action and harmonics, but the instrument is in tune, the action feels good, no excessive buzzes or dead spots.
I might consider making a proper reverse shim, but I will test it for a while. Thank you guys for your advice!:thumbsup:
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#19
Fabio_MIJ said:
Back again, I set up the instrument. I removed the shim, cleaned the fretboard, fixed the pickup to the body, and setup action and harmonics.
The bridge saddles are a bit to the endpoint for both action and harmonics, but the instrument is in tune, the action feels good, no excessive buzzes or dead spots.
I might consider making a proper reverse shim, but I will test it for a while. Thank you guys for your advice!:thumbsup:
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A Little advice...

Put a reverse shim in. The break angle over the saddles is a bit excessive. You also need to set the witness point on each string at the saddles. You will need to re-intonate, but doing so will add to both intonation and tuning stability.

Nice cleanup job.
 
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#20
Fabio_MIJ said:
Back again, I set up the instrument. I removed the shim, cleaned the fretboard, fixed the pickup to the body, and setup action and harmonics.
The bridge saddles are a bit to the endpoint for both action and harmonics, but the instrument is in tune, the action feels good, no excessive buzzes or dead spots.
I might consider making a proper reverse shim, but I will test it for a while. Thank you guys for your advice!:thumbsup:
View attachment 3596609 View attachment 3596610 View attachment 3596612 View attachment 3596614 View attachment 3596617 View attachment 3596619 View attachment 3596621 View attachment 3596624
Click to expand...

...good work, bro...
 
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