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Trek 2100 (Bonded Carbon)- loose DT shifter boss?

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Trek 2100 (Bonded Carbon)- loose DT shifter boss?

Old 04-09-21, 05:18 PM
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PatTheSlat 
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Trek 2100 (Bonded Carbon)- loose DT shifter boss?

Working on an early 90s trek 2100, one of the ones with the carbon tubes bonded to the aluminum lugs. The left side downtube shifter boss is loose and I can't figure out why. Anyone seen this before or know how these attach? There's what looks like a little flat head screw in there but I can't seem to get it to turn.

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Old 04-10-21, 04:04 AM
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Originally Posted by PatTheSlat View Post
Working on an early 90s trek 2100, one of the ones with the carbon tubes bonded to the aluminum lugs. The left side downtube shifter boss is loose and I can't figure out why. Anyone seen this before or know how these attach? There's what looks like a little flat head screw in there but I can't seem to get it to turn.

Hi I had similar isssue on a alu frame critter .
One side of the mount was fixed and part of the other rotated and tightened on threaded shaft that went right through tube .
I wonder if this is the case with yours ?

I have an assembly somewhere off a busted frame I should take a pic of too .
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Old 04-10-21, 07:37 AM
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The epoxy bond between the down tube and the boss had failed which caused the FD cable tension to pull up the leading edge of the boss to where it is, most likely, bending the screw that goes through the down tube, between the two bosses.
Getting the loose boss off the frame for re-gluing with epoxy, will be quite difficult, because of that bent, and possibly, corrosion seized screw.
Vitus used an almost identical design for their 979 and Carbone frame bonded on shifter bosses, and I still see replacement sets for sale on eBay, once in a while. You might consider getting a set to repair your frame, if you end up damaging the ones on your frame.
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Old 04-10-21, 08:53 AM
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Keep an eye on the frame joints if you ride it much; those frames have an unbonding history.
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Old 04-11-21, 07:13 AM
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It's the same deal with their all-aluminum frames from the same era. Along with other forum peeps, I had good luck with JB Weld, bought me another two seasons. I never replaced the screw, and ultimately it failed again, and it's awaiting some sort of bizarre 1x bar-end build at the moment. Talked with a bike shop owner a while ago who had one and he said he got that repair kit with the screw and it worked as advertised.
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Old 04-11-21, 05:52 PM
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This is only somewhat related, but does anyone know if you can use those bolt-through ones on a steel frame? Like if there were no frame builders in your area and you were reasonably competent at marking and drilling holes, is the steel on a bike that much thinner that it wouldn't suit this kind of attachment?
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