The cable guide (sorry, I don't know the technical term) where the rear derailleur cable attaches to the downtube on my Co-Motion tandem has mysteriously broken in half and no longer holds the cable in place. Since it is no longer held in place, the derailleur is currently inoperable. The frame is aluminum. Is there a (relatively) easy fix for this? Perhaps a camp on accessory that would serve the same purpose rather than having to repair the frame? Any guidance you can provide to help get the bike back into usable condition would be appreciated.[/ATTACH]

You need a "clamp-on cable stop". Do a Web search, here is an example: https://www.rivbike.com/product-p/ca6.htm You will need to know the size of tube it mounts on. You could probably securely zip tie the cable housing into what's left of your stop to get you going.

I doubt you'll find a clamp on stop for your OS tubing, but all is not lost.

There's a repair kit, which consists of a pair of bosses connected by a threaded rod which goes through the frame to hold them in place. Offhand I don't know the source, but I'm sure others will post pointing you in the right direction. This would require cutting the opposite one off, and filing flush to prepare the frame for the replacements. I suggest that you reinforce the job by use an adhesive, or something like JB Weld in addition to the bolt to secure them, so there's no tendency to rotate or work loose.

If you cannot find the kit, you might source a boss, cut off and file the old one flush, drill out the hole slightly and use a riv-nut to attach the replacement. In this case I strongly suggest bonding it to spread the load, otherwise it's likely to rip out taking the Riv-nut with it.

Here's the source info for the repair part I was describing Hopefully you can use it to solve your problem.

Francis references the cable stop design used by Cannondale and Klein, IIRC. The few times i dealt with this repair I was tentative about the design and repair process. Do your homework before blindly drilling holes in your frame.

In fact you might contact CoMotion long before you follow other solutions. A custom fabricated clamp that encircles the tube might be a more reversible solution.

Why did this happen? The most common cause of Alu. "braze ons" failure is a corrosive one. I have seem MANY top tube brake cable stops with much corrosion. I will try to remove as much of the white powder (AluOxide) as possible and coat the remaining with paint/lube to slow down the process. A few times the cable stop has significant shape loss. Andy.

I just reread my initial post and need to make a correction - the frame is chromoly. I was momentarily confused - must be the kids ;-)

I would LOVE to be able to use a clamp on cable stop - I haven't been able to find anything big enough for the tubing on this bike, though. I have already emailed Co-motion to see if they have any suggestions, which hopefully they will respond to after the weekend is over. As for Andy's question about how this happened, I'm not sure. The bike has been very lightly used and garage stored. My boys lost interest in riding the tandem with me much younger than I thought they would so it has well under a thousand miles on it. My daughter is just reaching the age where she can ride with me, but when my wife took her for a ride it came back broken. She said it "just came off" as they were finishing up the ride.

Thanks to all of you for your input!

Are you sure about the 'just came off' aspect? There's a big scratch between the cable stops and another on the opposite side of the broken stop.... almost like something impacted that area.

If you can't find a clamp on stop
and you don't mind appearances

take the barrel adjuster from an old shifter or caliper brake
strap it to the frame with a big hose clamp
bonus point if the hose clamp rests against the remains of the old cable stop; to prevent sliding
-dont try this on brake cable stops; shifters only

I agree about the "just fell off" statement as the rather deep scratches in the paint say otherwise.

Your first and best option is to talk to Co-Motion but if they can't help or it's too expensive, here is one "fix" that is permanant but requires a bit of work and faith in your abilities.

1. Grind off the remaining broken stub and the one on the other side of the downtube.
2. Drill a 5 mm (or 3/16") hole straight through the current stop base and all the way across through the downtube and out the opposite side.
3. Get a pair of Shimano downtube cable stops. They come with every STI or barend shifter set so most bike shops have a bunch of surplus sets.
4. Buy a 4" #10x32 bolt and a nut.
5. Run the #10 bolt through one of the cable stops, through the downtube holes and out through the other cable guide. Add the nut and tighten snugly. A drop of Loctite on the threads is highly recommended.
6. Cut off any excess bolt and file the end flush and smooth.

If the cable stops want to rotate on the bolt, bedding them in epoxy before installing the bolt will prevent it.

I did this fix on a friend's older Klein and it has worked perfectly for years.

I have brazed cable stops, pump pegs, etc. onto stainless steel band clamps to fit on oversize tubing.


HTH...

Done well, this is an excellent solution.

You'll need to purchase suitable steel bosses, either the standard lever bosses which take adaptors, or cable stops with a decent size base flange. Fit the clamp to the frame, locate where the bosses go, and mark the spots, and file the backs to match the curvature as close as possible.

Then remove the clamp, gently clamp it to a mandrel to maintain curvature, or simply adjust it to the right diameter, then braze.

If you don't like the cosmetics of this type of clamp, there are fixed diameter clamps which don't have the worm gear cuts and may look better.

BTW -- stops or lever bosses are notorious for slipping down the tube. To prevent this, sand an area on the underside, and epoxy on a formed piece of stainless as an anti-slide stop.

Less kludgy.. frame builder or just decent metal hobbyist shop.
The paint can be burned off, around that piece , the steel cleaned up , another stop brazed on,
and then some touch up paint re applied.

you could use a shifter braze on then add the cable stop/ cable adjuster/ shift lever boss cover
common to so many bikes, the boss itself is much more rugged,
surface to braze it to the frame tube is much larger.

That the frame is steel changes what I would do to repair the cable stop. And looking at the photo more closely changes my speculation as to the cause or the failure.

Being able to, I would remove the bits of the old stop and braze on a new one. This would damage about 6"+ of paint. For the short term I'd rattle can a touch up but would plan on a complete respray in time. I would also consider how I'd want the braze ons elsewhere be different given the complete refinishing.

My suggestion to have CoMotion involved if possible is still the first step and I would only do it myself if they were of no help. Andy.

Right. My drill-and-bolt procedure requires more surgery but the stops can't move once they are in place and no repaint is needed.

Of course the Shipping distance for the frame , being a Tandem, between the OP and Oregon
where CoMo is located, is a cost as would be tear down and rebuild ..

https://www.cycle-frames.com/bicycle-...=search&page=1