Tried the grub screw + Am Pro mod on my AOM Jazzmaster - my findings

[alexpigment]

One of my adjust-o-matic equipped JMs previously had an American Pro bridge on it, but via the method where you break off the posts, enlarge the holes and set it on the original AOM posts. I was never really happy with this (it didn't want to return to zero and tuning got sloppy), but since it was a 'backup of a backup' guitar, it never really felt pressing to address it. After reading about the method of using a grub screws with an American Pro bridge, it was always a mod I wanted to try, but it required getting a new Am Pro bridge since I broke the posts off of mine. Anyway, I found a cheap Am Pro with the 52mm spacing on eBay this weekend and decided to buy it and try this method out.

First I ended up buying a set of grub screws on Amazon that had multiple sizes of M8 grub screws, just in case one worked better than the other. I learned that if you screw the 8mm tall M8 all the way down, they get stuck below the threads of the thimble and just kind wobble around down there. I used a clever method to get them back out and then tried the 12mm M8 grub screws. Those didn't get stuck under the threads, but they also never got tight. I tried adding some solder to the threads to create some added pressure, but the solder never would 'take' on the screw. So I decided to put some pickup height springs under the 8mm M8, and this worked out really well. Lesson learned #1: use springs under the grub screws.

After that was all said and done, I strung it up and noticed that the bridge really didn't have a natural resting position. It wanted move forward naturally and I kept having to push it back. I tried adjusting the bridge's height screws (which are pointed rather than flat) up and down to see if that would help, but it really didn't change anything. So I decided that the screws needed a smaller hole to pivot on. Looking around in my set, I saw that I had some 4mm M4 grub screws, and so I put them nested in the M8 grub screws (a bit of a russian doll situation). This was actually perfect, since now the bridge height screws had a centered small hole to pivot on. Lesson learned #2: put a M4 4mm grub screw inside the M8 8mm grub screw with the hole facing up.

Overall, this works pretty well - definitely better than before. Tuning is stable under normal use, but now I'm dealing with this "tuning goes sharp if I pull up on the trem" issue that another user posted about recently. It's not severe, but it happens. I think it may be related to the tremolo's spring. When I set this guitar up, the correct tension to get the trem lock working made it such that the tension screw was at its loosest point. Loosening any further makes the screw stick up from the trem plate. I'm going to try an AVRI spring first, and if that fails, a whole AVRI trem. Currently, it's got an MIM on it.

Lastly, I just wanted to mention that I have two other AOM guitars with Staytrem bridges on them (with the conversion posts that screw down into the existing thimbles). I gotta hand it to them for making such a good design that *just works*. I went through a lot of trial and error tonight to approximate something that the Staytrem guy perfected. I'd order another one in a heartbeat if they still shipped to the US.

Sorry for the long post. I hope this is helpful to those trying this mod in the future. Here's the grub screw set I bought for what it's worth ( https://www.amazon.com/gp/product/B07L73K16W ).


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[601210]

I love the idea of sticking springs in there, and it's nice seeing popular forum mods actually being tried out and reported on rather than just being passed around like folklore.

I think some of the suggestions I've seen involved using grub screws with cupped ends and installing them from the bottom. It would solve your problem of the hole being too large and flat, but then you'd have to take the thimbles out, screw them in at just the right position, and then reinstall the thimbles and hope you got it right the first time.

The Staytrem design is actually really clever IMO because instead of a pivot in a cup, it's more like a ball-and-socket joint and what that does is let you screw it down from the top, while still having a good surface for the rocking action. Can't imagine it being cheap at all to manufacture so I can kind of understand why he stopped doing those even before he stopped shipping worldwide.

Maybe it would be possible to use little metal or even nylon cupped discs that would drop in on top of the grub screws to give you that ideal surface, although it introduces even more little parts that could shift around and heaven knows we have enough of those on Jazzmasters

[alexpigment]

Maybe it would be possible to use little metal or even nylon cupped discs that would drop in on top of the grub screws to give you that ideal surface, although it introduces even more little parts that could shift around and heaven knows we have enough of those on Jazzmasters

If I understand what you're saying correctly, I think my method effectively does this. The hole in the smaller grub screw is too small for the height adjustment screw/spike of the bridge to go down into. But since that screw/spike is pointed, the tip of it protrudes into it. That means that it's not prevented from rocking, but it has a natural center that it wants to go back to.

[timtam]

The spring sounds like a good idea. Or maybe loctite.

These are the cupped bottom M8 grub screws originally suggested for this approach. Is that what you tried and they didn't work well ? Or did yours have the more usual round-ish bottoms ?

http://www.offsetguitars.com/forums/vie ... d#p1574786

[alexpigment]

The ones I got had flat bottoms and were silver. I can't imagine it would have made any difference though unless I installed them upside down. I don't think pulling the thimbles and doing that was really ever an option in my mind due to the huge-pain-in-the-ass factor.

[timtam]

The ones I got had flat bottoms and were silver. I can't imagine it would have made any difference though unless I installed them upside down.

That's the whole idea of the cupped bottoms ... install them upside down so they mimic the bottom of the conventional thimbles that the bridge post screws are used to sitting on.

Anyway ... glad your solution worked.

[alexpigment]

That's the whole idea of the cupped bottoms ... install them upside down so they mimic the bottom of the conventional thimbles that the bridge post screws are used to sitting on.

Anyway ... glad your solution worked.

Well, consider this the "less invasive, easily adjustable, 1-day-shipping available" method

[timtam]

Avoiding having to remove the the tunomatic bushings to insert the cupped bottom grub screws upside down is a legitimate concern. However they can be removed easily with a M8 bolt, washer, and short length of pipe ....
https://www.youtube.com/watch?v=Q1ppKxEIF1M
Or Elmer and Shatten make a commercial bushing puller ...
https://elmerguitar.com/knob-and-bushing-puller.html
https://schatten-pickups.myshopify.com/ ... uller-tool
https://www.ebay.com/itm/Guitar-Knob-Bu ... 3150224512

[alexpigment]

That's an interesting method, and very nice to know for the future. I appreciate the links, and will almost certainly refer back to them at some point.

Having said that, part of this process was really just taking this idea that I'd seen on the forum (and perhaps misunderstood slightly), and really testing it out to see if it has merit. I think the method I arrived on actually has some advantages, since that the bevel of the bridge's height adjustment screw doesn't need to match up with the cup of the grub screw. I would have to buy the grub screws in question to see, but I doubt that they are a 100% match in terms of conical shape. Having a hole to for the height adjustment screw to poke down into really takes that out of the equation. There should in theory also be a greater transfer of string energy to the body.

Additionally, it's seems a bit easier to me for the average person to attempt this. I hope that between the illustrations and the link to the actual product I bought, it should be approachable to a novice who might be hesitant to remove thimbles. And if you decide to sell the guitar and want to put it back together, it's a quick 2-minute job to re-install the AOM posts and bridge.

Anyway, I'm pretty happy with how it turned out. Not as ideal as the Staytrem, but far better than the other method of using an Am Pro bridge that I had tried before.

[sugarandopium]

This thread should be a sticky.
I’m going to try this out next week.

[alexpigment]

This thread should be a sticky.
I’m going to try this out next week.

How did this work out for you? I was just playing around today with the guitar that was the basis of this thread (it had been in a case for several months), and was really surprised by how well the solution has worked in the long run.

By the way, there are two updates: 1) I put an AVRI trem on the guitar a while back, and all the tuning instability went away with trem use; it's now 100% stable. 2) I put a standard (AVRI) bridge on it after being dissatisfied by the American Pro bridge's lack of individual string height adjustment. I really dig the stock bridge, and due to the trem placement being closer to the bridge, there are no issues with strings popping out of place on the threaded saddles. It actually sounds a lot more "lively" than my other JMs.

As always, I recommend reverse-shimming guitars with "modern" trem placement. An effective angle of 0.25 degrees should be about as much as you'd ever want/need, and that is on the extreme end for me. Forum members putting 1 degree shims in their guitars with pre-angled neck pockets feels a bit nuts to me