Vintage trem sticking

[Gavanti]

I have a tremolo unit in a '68 Jag that appears to be sticking, impeding smooth motion. I have pulled the unit and it works fine out of the guitar. In fact it works well until I tune the strings. The lock button is out of the way. Is it possible that the edge of the plate is catching on the wood at the back of the trem route? There's a groove in the corners of the routes (which I've seen in pics of other CBS offsets), and on the left side, there's a bit of a ledge. If so is filing the ledge the answer?

[url=https://flic.kr/p/Uz2iiJ]
[url=https://flic.kr/p/TwTN6S]

[antisymmetric]

When this sort of thing happens to me, I get in there with some crayon and apply it to the trem itself or the cavity, reassemble/ test and see what other surface the crayon has transferred to.

[theworkoffire]

It's more likely to be rubbing at the front or possibly the sides of the cavity.
Check that the string retainer is perfectly centred in its slot.
If it's a recent problem, it could be that the blade that floats the string retainer is worn. The crayon trick is a good idea - or line the edges of the cavity with loosely pressed masking tape. You may need to fill the mounting holes and re-drill slightly if it needs re-aligning.

[Gavanti]

Thanks. The guitar is new to me, so I'll have to do some more investigating. Unfortunately, with the problem only manifesting when the guitar is strung to tension, it's going to take a lot of disassembly/reassembly. These suggestions will hopefully cut some of that down.

[Gavanti]

I tried the crayon transfer trick but couldn't tell where it had transferred. I'll try lining the cavity tomorrow to see if that reveals anything. It's definitely sticking on something. The trem plate floats, but if I push it down or pull it back up at tension, the floating plate will hit two distinct stopping points as it travels. My guess is it's not the trem parts, but I have parts of a vintage unit and an AVRI unit around, so I may do some transplanting to see if that helps at all. The screw holes look really clean and hold fast too, so it's hard to imagine the trem has shifted, but I guess that's possible. The trem lock button definitely gets pushed back toward the floating plate when installed but not so much that it seems to be catching the plate.

I definitely get more nervous about taking things apart than on my other guitars...kind of grateful that Fender started using poly in '68.

[antisymmetric]

I wonder if the problem involves the spring in some way- what you're describing sounds like what was happening on my old Jansen (early '60s NZ- made, very Fender offset- derived) trem, which was corrected simply by loosening the spring tension. Or maybe that threaded part that the bottom of the spring presses against- binding inside the spring somehow? (just throwing out guesses here, could be way off base )

[Gavanti]

I wonder if the problem involves the spring in some way- what you're describing sounds like what was happening on my old Jansen (early '60s NZ- made, very Fender offset- derived) trem, which was corrected simply by loosening the spring tension. Or maybe that threaded part that the bottom of the spring presses against- binding inside the spring somehow? (just throwing out guesses here, could be way off base )

Thanks. That's definitely possible, but I have tried tightening and loosening the spring tension, and that didn't seem to make a difference...unless I need to shorten the spring or something like that. The floating plate actually gets stuck in such a way that changing the spring tension doesn't change the level of the floating plate as it would if it were operating normally.

As I think about it more, I'm wondering if the reason that this only happens at full tension and that movement catches at the two plateaus has to do with the interaction of the knife plate and the string retainer plate. I'll hit the parts drawer tomorrow.

[Gavanti]

It's apparently not the string retainer/knife plate interaction. I swapped these parts out with ones from a unit that I know works, and I'm still getting the double stops. I've got the trem floating between them right now. Downward movement is workable but not smooth, and the guitar detunes quickly. Upward movement results in the trem getting stuck. The bass end of the string retainer seems to be jumping out when it goes past the upper of the two stops. This really makes me think that shelf in the route at the back corner of the bass side might be either the primary cause or a contributing factor resulting from some other element. It does look pretty scraped out on the bass side, definitely more than on the treble side. My thinking is that the bulge in the string retainer plate is catching it early in its travel downward, popping in and sliding along it and then popping out more gently as it goes down.

I'm not certain what the interaction should be between the string retainer and the back wall of the route? Does the string retainer plate slide along that wall evenly to keep movement balanced? Is supposed to float past without touching it at all? I know with aftermarket bodies the recommendation is to square off the back corner of the route, but I always assumed that was for corner clearance. This post suggests that a rounded notch at the back corners was pretty typical of 60s Fenders.

I don't mind filing/sanding down that ledge down if that's at all likely. I start getting a little more concerned about skill and potential devaluation if the cavity needs to be enlarged evenly or the trem unit needs to be relocated.

[andy_tchp]

No interaction; it shouldn't touch at all.

If (with the screws and string tension removed) you move the assembly around slightly in the route then attempt to move the arm up/down does the behaviour change at all? I'd be trying to bring the assembly forward (towards the headstock).

[antisymmetric]

Another thought- do you have another guitar with trem that's known to be ok? Maybe you could try swapping trems around to see if the problem could be isolated that way...

[Gavanti]

Ok, so Ben nailed it. I used masking tape and a china marker, and the floating plate is apparently shifting forward and hitting the front wall of the trem cavity. I think the hard click must have been its passage over the ground wire. I've got an AVRI knife blade in there now I think, so I don't think that is the problem. I'll try to assemble a whole AVRI unit from my parts just to see if that addresses the issue, but it seems like the unit was either aligned wrong to begin with or that it didn't have much tolerance and has shifted forward over time. That would mean filling and redrilling, yes? That's unfortunate as the guitar is otherwise fairly clean, but a functioning trem is pretty essential.

Jag Trem
Jag Trem
Jag Trem

[Gavanti]

So I guess the other question is does it make as much sense to sand or rout material off the front of the cavity? I saw that another member had resolved a similar problem that way rather than repositioning the trem. I got a decent deal on this, so I guess the repair cost is karma. Also, this is my first vintage guitar that isn't fairly low value or already a beater; I should probably ask folks who know more about these things if there would be a significant hit to value from the repair.

[MrFingers]

Maybe replace the "anchor" (the plate that gets screwed to the baseplate with the 3 bolts, and acts as the pivot for the vibrato-plate itself) by a new unit? Chances are in the 50 years it has worn so much that it allowed to plate to shift forward. That's a non-invasive mod you could try.

[Gavanti]

Maybe replace the "anchor" (the plate that gets screwed to the baseplate with the 3 bolts, and acts as the pivot for the vibrato-plate itself) by a new unit? Chances are in the 50 years it has worn so much that it allowed to plate to shift forward. That's a non-invasive mod you could try.

Thanks. I did try to replace the anchor with one I knew was working well. Next time I get a chance, I think I've got a whole AVRI unit on another guitar, so I'll try a full swap. If that doesn't work, I think it's going to the shop.

[Gavanti]

Everything on the trem checked out as working correctly and in good shape. So far as my luthier could tell, this one may have left the factory with an overly tight trem route. Luckily the Mastery vibrato has a short string plate to increase clearance, so now this old Jag is fully operational.