Sora thumb button breakage -- fix with epoxy?
 

My cousin didn't really understand how to operate the Sora thumb buttons on my nearly-unused Burley tandem, and snapped off the left one. I was about to blame the seller of the bike for selling me something that must have clearly had significant plastic fatigue already, but then heard from a mechanic in a bike shop, as well as in other threads on the forums, that this part is fairly prone to breakage. I can't really blame my cousin, since this part really has no excuse for having been engineered in such a way that it would be *that* easy to break.

Now, I know the obvious solution here, since Shimano doesn't sell parts for rebuilding its brifters, is to either replace the whole left brifter with anything that can shift a triple, or to very carefully cobble together the parts from another differently-broken Sora brifter. But I'm nerdy and I'm cheap, so I'd really like to try to see what I can do to plastic-weld it back on. I mean, it was plastic in the first place, so how much force should it really need to take? I suspect that by using a very strong epoxy and "bandaging" the broken joint with the stuff, I probably ought to be able to reinforce it to the point that it might even be stronger than it was to begin with. I'm not averse to filing off a bit of the plastic around the slot between the hood support and the brake lever, to accommodate the thickened thumb lever arm after its plasticky reinforcement is in place. I've also considered the idea of drilling into the remaining part of the arm and attaching an improvised lever to that, but I imagine that would be unlikely to work unless I tried something along the lines of what this guy did: http://bikeforums.net/attachment.php...6&d=1153880455

Actually, I suppose a really cool fix could be to replace the whole plastic part with a piece of metal machined and bent to be an exact replacement, but I don't want to try to undertake that complicated and time-consuming of a fix before at least trying the plastic weld idea.

Anyone here have any suggestions (other than "replace the whole thing", which I am already considering but hate the idea since the rest of the brifter works perfectly well)? Any particular recommendations for epoxy materials to try for the bandaging approach? Any input would be much appreciated.

When your fall back option is to replace the whole thing, you can afford to mess around with the one that you have because you have nothing to lose other than time.

If your objective is to make the bike rideable, I'd replace the whole thing because that's what I think is going to have to happen anyway.

Sounds like a job for JB Weld.
Top

+1 :o

+2

Why does everyone want to continually dick around when they can just fix the thing and be out riding.:mad:

Tim

Warrantee... We had a shifter like that come through and we warrantee it.

I don't think anything's going to stand up to the shear force of pushing the lever down. But hey, give it a shot. Just make sure you're on your middle ring so that you can make it home with a reasonable gear range.

The modification shown in your link was attached to the lever by a piece of safety pin with thread wrapped around, all held together with epoxy. I had to bend the piece of safety pin so it hooked over the inside end of the lever, otherwise it would pull out from the binding. A piece of wire like a paper clip bridging the break will provide all the strength you need to reinforce the epoxy.

Sora thumb button breakage--compete STI disassembly, epoxy fix, and rebuild
 

OK, so, this got picked up and put down on and off again for a few months, but last night I finally fixed it. You all should make tremendous fun of me for not just giving up on this, but I'm a tinkerer by trade and this became an obsessive challenge for me. I had a spare MTB front derailleur friction shifter that I could use anyway so this was not going to prevent me from riding the tandem on a long trip (and even so, I didn't really need the derailleur for short trips in super-flat Boston, anyway).

Turns out that this part is actually metal, not plastic as I had assumed earlier--the plastic is only the fused-on button part itself. I tried bridging the break with JB Weld with a bread tie wrapped around it, but the break was too close to the center to make a stong weld (broke again very easily without me reassembling it at all), so I figured I wouldn't get a good enough weld without taking the thing apart to the next level, so I did. At that point I realized I wasn't going to get in there further without taking the pod itself apart, so I did, taking pictures each step of the way for reference, down to the spring-tensioned white "pod" itself, which I left tensioned together with bread ties.

For a stronger brace, I used a metal picture frame hanger (see the very last photo in the last set--I used the 30lb type) which I cut apart at the nail eyelet, and using a small Dremel bit, widened the eyelet into a notch just long and wide enough to actually slip around the joint and provide a firm grip. Using pliers, I then twisted the rest of the frame hanger around the joint up to the remaining metal and that really held it. I covered the whole thing with JB Weld, and once cured, Dremeled it down to give just enough clearance so that it could operate without catching anything. (I erred on the side of leaving just a bit too much, and once the whole thing was fully assembled, I did some hand-filing with precision files just to clear the last places where it was getting in the way.) I wish I had some pictures of this before I epoxied it, but I forgot.

I tried to keep the spring-tensioned parts together, but at some point I slipped and they all exploded in my hand, and I didn't have any pictures to reference that far in. I assembled and disassembled it a couple of times tensioned incorrectly, and gave up again for a while, but last night I picked it up again and got it all figured out. The trick was to catch the big spring in the center in the one place where the pointing part would fit all the way into its deepest groove at the bottom, and then crank it tight by fitting the upper part in and rotating until its notch fit in place. I wasn't sure which of my attempts at this would work, so I stopped taking pictures at this point, but Geoff's site (see below) should be helpful, and along with that, hopefully you can get the idea from the video of the reassembled pod in action. I'm attaching all photos here and to the next posts, and I'll upload the videos somewhere and put in a link.

There's a serious lack of documentation on the insides of STI shifters (surprise, surprise). This guy did a fairly full rebuild with a mountain bike shifter -- http://www.cs.hmc.edu/~geoff/deoredx/index.html -- and a lot of what he says applies, but I found his instructions a bit difficult to translate to the road stuff, so maybe these pictures will be helpful to anyone working on road shifters, and I emailed Geoff to tell him and ask him to put in a link. I feel like I really understand how they work now, and could rebuild one again now with much less trouble.

Full set of photos below, going from the point where the Shimano documentation leaves you hanging out to dry (at http://techdocs.shimano.com/media/te...9830609256.pdf ), to fully disassembled, to fully reassembled.

More photos

Even more photos

Even even more photos

Even even even more photos

Last batch of photos

That is an awesome contribution to literature on STI/brifter repair, at the least.

Thanks a million.

If you replace it, since it is a left brifter, upgrade to Tiagra or better. This may sound a bit foolish with a Sora on the right, but the paddle shifter will handle the stress better. Heck, you can upgrade both to R-500 brifters to maintain the 8-speed.

Wow, that's a great job! But, what in the world is the 4 conductor ribbon cable for?!!!

Thanks! That's for the Shimano Flight Deck feature. There's some sort of electrical conductivity sensor for upshift and downshift that trips when you shift and feeds through the ribbons. If you have a Flight Deck computer (I don't), you plug the ribbon cables into it through the hatch that you can see in IMGP1558.JPG:
http://www.bikeforums.net/attachment...9&d=1215965392
and it will sense your shifts and tell you what gear you're in.

Here's the instructions from Shimano:
http://bike.shimano.com/media/techdo...9830604501.pdf

Check out chapter 7, on page 16.

I was reminded of this thread today by dnuzzomueller's signature -- http://stiteardown.0sites.net . The step-by-step instructions there are much better organized than my vague descriptions and stream of pictures! It's interesting (but not surprising) to see how many more parts on the old Ultegra are made out of metal as opposed to the plastic on my Sora.

I also decided to search to see if anyone else had done it since, and saw Kimmo's thread: http://www.bikeforums.net/showthread.php/610670

Here's another great set of step-by-step instructions, specifically for Sora:
http://www.instructables.com/id/Serv...Sora-Shifters/

FYI, in spite of what all the haters predicted, my JB-Welded, metal frame hanger-reinforced thumb button repair is still going strong. :)

Pocky, that was quite a job you did, my hat's off to you. Were it my Sore-ah brifter, he would have been introduced to Mister Hammer. ;)