Univox hollow-body truss rod

[Bluelick]

Greetings,
I have a Univox hollow-body bass (335/EB2 style, with the bolt on neck, made in Japan, early 1970's, "lawsuit" headstock). It is the bass version of the Univox Coily six-string.

When I got it the truss rod nut was stuck on, and today I was able to get it loose after letting it sit with a couple drops of penetrating oil on it for several weeks. By the way, the truss rod nut on the Univoxes of this period (or at least the bass and the Coily six string that I have) have a hex socket nut that uses a 5mm allen key, and they have a hole in the bottom of the allen socket that will allow a drop or two of penetrating oil to work it's way in to the threads. I was able to remove the nut on my six-string to verify this before I set to work on the bass.

Sorry for the long prologue, here's my question: Does anyone know if the truss rod on these was a double rod, or a square-channel type, or what? While I appreciate speculation based on similar basses of the period or others, I would really value information from anyone who has actual knowledge of the truss rod used in the Univox Coily bass.

Many thanks!

[Pilgrim]

I'll wait and see what you learn from others. I have a similar Univox hollowbody and as far as I know the Japanese basses of this era had conventional, simple truss rods. It's a very nice bass, although the pickups are nothing special. I've made adjustments on a couple of Univoxes and Lyles, which are essentially the same since the Matsumoku factory made a number of models with similar design features.

I would bet coffee and donuts that Matsumoku used nothing but a conventional truss rod. I know it's not a double rod in that model, and I've seen no evidence of them "wasting" money on a square-channel rod. I also wonder why it matters. All that matters is whether the truss rod works...and I hope yours does.

[Bluelick]

I can now furnish more information on this neck and truss rod having removed the fingerboard yesterday!

I was trying to straighten the neck (which had a pretty good bow) with the truss rod when I heard a loud pop in the neck, the kind of sound you don't want to hear. I could see the truss rod was now pulling up through the neck as I tried to tighten it. I knew I was now in over my head, so off to the shop of my friend the luthier for a consult. Long story short, one of the luthiers was able to tap a chisel at the end of the fingerboard at the nut (nut off) and get it started. The crystalized glue gave way pretty easily and working a spatula under it he had the fingerboard off in just a few minutes. This was a best case scenario, as they had originally talked about having to remove the binding, heat the fingerboard, etc.

What had happened apparently is that the truss rod pulled out of the bar at the end that it had been threaded into. It might have already been mostly unscrewed at that end by the look of it. There is a single action truss rod in the middle with wood spacer blocks above it, and steel rods set in on either side. I'll take pictures and post them as I proceed rather than trying to describe it.

By the way, the truss rod nut was stuck when I got the guitar. Among the possibilities as to how the rod came loose at the wrong end is that it unscrewed down there when I was trying to loosen the nut.

Plan A will be to flatten the neck, reset the truss rod into the stopper and reglue the fingerboard.

Plan B would be to replace the truss rod with something a bit more elegant.

I need to get into it a bit to determine the best way to go. As I said, I'll post pictures and all comments will be welcomed.

[Bluelick]

Here are some pictures. Note that the two shiny nuts at the top of the truss rod are nuts that I drilled out the center of to serve as spacers. The truss rod nut is not shown in the picture.

[Pilgrim]

Yes, looks very much like the truss rod nut was tightened, then froze on the rod - and later attempts to adjust it resulted in unscrewing the rod from its anchor.

Glad you got at it with minimal work and damage. Nice looking neck - and those offset dots are pure Matsumoku!

[Bluelick]

Yes, the neck is pretty, and there is no visible wear on the fingerboard. I think it sat in a closet with some heavy strings on it for 40 years or so without being played and the neck took a bad set.

I thought the steel rods on either side of the truss rod were interesting. I suppose these give the truss rod something to push against when it's tightened and reduce the potential for twisting.

[Pilgrim]

That also helps to explain why the neck is a little heavier on these basses than on some other short-scales. I've always been surprised that the neck is as heavy on mine.

Here's a photo or two of my Univox...mine has the earlier headstock logo and block inserts instead of the dots.

[Bluelick]

I see you have flats on there, what scale strings did you use? I am thinking that with the tailpiece, short scale strings will be too short and I should go with mediums.

[Pilgrim]

Right! These basses require medium scale strings (32") because the bridge and tailpiece design is different from solid bodies...the strings must be longer relative to the scale length. I'm using light gauge flats - don't recall which brand, but if I were to replace them (unlikely, they've only been on there about six years and sound great) I'd use Labella 760FL-M (.043-.104, medium scale) strings.

I see from the headstock close-up that I need to re-check the G tuner; when the picture was taken it was wound incorrectly. Tsk, tsk.

[who1981]

I just got a Univox Violin bass (the strange one with the scroll headstock) for $100! Sounds great, and it's a real eye catcher. I'd bet it's made in the same factory as your bass, as it has the offset fret-dots and the truss rod nut is exactly as you describe.

Upon trying to tension the truss rod to take a bit of bow out of the neck (loosened and oiled a bit first)...POP... and the truss rod just spins.

Unfortunately my luthier friend isn't too keen on popping the fingerboard off...so I'm likely stuck taking it to a spendy shop.





PS. The pup and wife both dig the scroll headstock

[Bluelick]

You are in exactly the same boat I was in. Keep in mind that the "spendy place" may want to do the full monty, which is remove the binding before taking the fingerboard loose, and it may not all go back on so nice. That's what the luthier wanted to do with mine (or said should be done, he was not really recommending spending that kind of money either). It took about 30 minutes of saying "isn't there an easier way?" to finally goad him into trying to pop it off with a chisel. If your fingerboard hasn't been off and re-glued, I bet it comes off just like mine. Once you get it off, be sure to sand that neck flat before you reglue it. I did that with sheets of sandpaper face-up on the table of my table saw, it worked great. I took the rod to a welding shop and had the tail end brazed back on, with a nut below it for good measure. Had to thread the rod a little to make room for the nut, then I chisled out the pocket to make room.

[Pilgrim]

I LOVE those scroll-headstock basses! That's worth more than $100 for sure...although you need a functioning truss rod.

Bluelick is right - once the fretboard is off, you MUST sand both surfaces to get a clean contact area for re-gluing.

I'm not sure it's not worth going in regardless - with a good truss rod, that's probably a $350+ bass with the case.

[Bluelick]

I agree, that headstock is very cool.

Now to be clear, the sanding is not just to get the surfaces clean, it is to sand the bow out of the neck. If it's like mine was, it's three pieces of laminated maple, and probably has been in a bow like that for decades, you won't be able to straighten it even if the truss rod is working right. But it shouldn't move again once you straighten (flatten) it by sanding it against a perfectly flat surface (table saw table, big piece of thick glass, granite counter top).

I'd suggest you go to one luthier after another until you find one that will take a reasonable approach to this, or do it yourself. In the interest of full disclosure, I am NOT a luthier, but I do have many years of experience as a woodworker and have done a few guitar-related projects.

Keep us posted.

[Bluelick]

OK, I realize that I had promised to post pictures of the repair and never got back to it, but maybe these will be helpful to Who1981 and others.

Here I have extended the treads on the rod and added a nut for better purchase. Also chisled out the pocket in the neck to accommodate the nut.



This shows the rod peened over so it cant unscrew.



Here you can see the 80-grit green sandpaper clamped to the table saw to flatten the neck.



In this picture the neck is partially flattened, as you can see by the clean surfaces at either end.



Continued in next post

[Bluelick]

Truss rod repair continued

This shot shows the nut brazed onto the rod. Maybe it's overkill but I didn't want to have to do this ever again!



I wrapped the rod in teflon tape so it would not get bound in the channel.



The bottom of the channel is concave and the rod is held down in the channel (with a bow) by three wooden blocks. I had cut these blocks out with a small backsaw to get the truss rod out. I replaced them with small pieces of cherry left over from a dining table I built. Nice Kentucky hardwood to complement the maple neck (and never to be seen again but I know it's there). This picture shows the rod clamped down while the blocks are glued in.



Continued in next post

[Bluelick]

Truss rod repair, part three

I drilled a small hole at the heel of the neck and glued in a cut off piece of a small nail to index the fingerboard so it wouldn't slide around while clamping. I dry fitted the fingerboard and pressed it down on the nail to make a matching indentation in the right place.



I put masking tape over the truss rod cavity while I spread the glue on the neck, then removed the tape before putting the fingerboard on.



Finally I clamped the fingerboard on, using the index pin at the heel to locate that end, then working my way up the neck aligning the fingerboard to the neck as I went up the neck.



Questions or comments welcome, I hope this is useful to someone.

[who1981]

Wow, thanks, that's super helpful!
I might just give it a try.

[Pilgrim]

Nice work, and indexing the fingerboard was an excellent idea. It's much too easy for a project like that to slide off-center!

[josef83]

Hi.
I have a hollow-body Univox bass. I've had it since I was a kid and I'd appreciate it if anyone could "school" me on it. How do I know when mine was made? What is Univox? Are these guitars rare, valuable, significant in any way? I just love looking at and playing mine. Mine looks like Pilgrim's but my pickups have a black strip on the top and the headstock is just wood, not black, and it looks like there may have been a label on the headstock at some time but is lost.

[Bluelick]

Univoxes were made in Japan in the same factory as the Japanese Epiphones of the early 1970's, shared many parts apparently. The Uni's are probably less valuable than the Epi's in terms of market value, but I like them a little better.