Thunder Horse

My beloved training bike, Mongoose IBOC* road bike, has a broken derailleur hook. It happened as I got out of the saddle to climb a hill.

The seat and chain stays are alloy. Please tell me that there is a way of replacing / repairing this problem.
OR that if the part cannot be located that perhaps another derailleur hook and derailleur could be incorporated.

Please don't tell me to replace the whole bike. It's a vintage bike by now, even though it has three lengths of carbon-fibre tubes in the triangle.

* International Bike Of Champions (IBOC).

mrrabbit 

Great candidate for a single speed or fixie!

=8-)

(There, didn't have to say it...)

=8-P

HillRider

The dropout has (had?) an integral derailleur hanger so it can't be replaced without replacing the entire dropout and that will require the services of a frame builder. Given those parts are aluminum even most frame builders won't be able to help. A welder whose good with heliarc and knows how to weld aluminum could probably repair that break.

Another alternative is to find a "claw mount" for the rear derailleur. That's a bracket the derailleur bolts to and is clamped under the quick release nut. Crude but passible.

Marcus_Ti

another less painful way of saying it: "wall art".

SkyDog75

Most newer bikes have replaceable derailleur hangers so that failures like this aren't catastrophic. Just unbolt the broken hanger and bolt a new one one. Since that's not an option for you, it'll take a little improvisation to get your bike working again.

If your frame was steel, a framebuilder could remove the damaged dropout and braze in a new one. But many aluminum alloys need to be heat treated after welding and that's problematic -- especially since your frame's partially carbon.

So if welding's out, you need some way to mechanically replace your derailleur hanger. You can use a claw, a Problem Solvers universal derailleur hanger, or you can modify your dropout and what's left of your derailleur hanger to accept a bolt-on hanger. Yellow Jersey's web site has a few examples like this one of modifying a dropout to accept a bolt-on hanger.

Thunder Horse

Thank you mrrabbit, HillRider, Marcus Ti, and ShyDog75 for your input and valued advise.
I am following up on the 'claw (No! Craw*) mount, and universal derailleur hanger ideas.
I have already sent this info to a friend of mine who is a retired cycling mechanic, to get his opinion as well.
Thanks again.

* Maxwell Smart always called the 'Craw' the Claw, and drove him mad about it.

WizardOfBoz

Agree with others on actually "fixing" the hanger. After you weld Al, you have a "heat affected zone" in which the heat treatment of the aluminum is not adequate for use (either your new welded hanger would likely break off again in use, or your chain or seat stay would). In the factory, the Al parts are heat treated. Then assembled with the CF tubes and painted. To weld this, you'd need to remove the cf tubs (probably destructively) heat treat the rear triangle, reassemble with new CF tubes, and repaint. It is not practical to do this.

You could lurk on eBay to find your exact frame (or another that is a couple years younger and has a replaceable hanger) and swap it out. That's probably what I'd do.

But you love that frame, and the heart has reasons that know no reason. So.... You can use the claw (craw) hangers. Have an LBS or machinist friend (or you - carefully) prepare the existing dropout with a saw and file to fit the claw you buy, and then you're QR skewer will hold the claw on. If you get the right hanger, and craft your dropout to fit it like a glove, your QR will be more likely to hold the thing together rigidly.

It may end up that every time you remove the rear wheel, you have to reinstall the claw+derailleur. But your beloved steed will remain with you, and not as a steam punk/wall art display on the wall of the local chain restaurant.

corrado33

I doubt you'll be able to use a claw type derailleur hanger. Those are built to be used with horizontal(ish) dropouts, not with modern vertical dropouts. The angle would be all wrong.

And this bike is a bad candidate for a SS or IGH because of the vertical dropouts.

Buy another frame, many more out there like it or better than it.

That dropout hanger was already on it's last legs as it was using a derailleur hanger saver (nut on the back) which meant you had to drill out the hanger to a slightly wider diameter in order for that to fit.

You had to know that was only a temporary fix... right?

Besides... 30 year old carbon fiber bonded to aluminum lugs? Yeah, if it hadn't broken yet it was well on its way anyway, especially for a mountain bike.

berner

I used to work as a boat builder. At one yard we built custom aluminum boats up to 60-70 feet. I don't weld myself but some of the guys were magicians at it. They could weld a beer can to the side of a hull. If you found someone like that, they could fix your bike.

DiabloScott

OK, you don't have to replace it, but you do have to throw it away.

WizardOfBoz

+1 This is probably the best insight: older CF is not as durable as later CF, and with the 30 YO CF tubes, plus the 30 YO glue joint....

fietsbob

2nd picture looks like it already had to be bodged a bit when the derailleur hanger got stripped threads

so a steel repair piece insert was installed.

Thunder Horse

Thanks for info. Perhaps Loctite will keep the claw in place while carefully removing the back wheel.

In regards to steampunk artwork, well that is a possibility, but a second last resort.

Thunder Horse

Thanks for info.
The earlier link by SkyDog75 to the universal derailleur hanger, in the tech details, said it is usable for most horizontal and vertical dropouts.

No, I did not know that at all. It was second / third hand when I got it. And have ridden many thousands of miles without having to replace the derailleur.

You have a point there, but it is not a mountain bike, but a road bike.
If I get the derailleur repaired, and with regard to your statement, I will continue to use the bike only on the flats.

Thunder Horse

Thanks berner, but the heat treating bit with the Carbon Fiber tubes is a concern.

Thunder Horse

Last resort. But I am a racer and will try all options before conceding.

Thunder Horse

Yeah, I just had a closer look. I took the nut off. The derailleur thread is fine, but the nut head looks mangled.
[EDIT: Yes you are right, the thread in the alloy hanger got stripped. I can see some of the previous thread in the hole.]

Also there is not much alloy meat, on the hanger, around the nut. That, plus the derailleur catching a spoke, easily broke that thin part.

So I will need to replace the derailleur. The original was a Shimano RD 2300 9=speed.

corrado33

Ah, I see that. the only problem I can think of is that it'd bring your derailleur out by 5 mm or so, possibly making it impossible to reach your easiest gears.

EDIT: By the way, those problem solvers aren't meant to do what you want them to do. They're meant to be carried to replace all types of derailleur hangers on bikes equipped with a replaceable one (since they're often different shapes.) You may be able to do something by grinding parts of what's left away to try to fit a modern derailleur hanger on it (then screw the hanger on.) but it'll always be a bodge and on a frame like this, with such a limited lifespan, it's not worth it (in my opinion.)

If you REALLY want to fix it. Buy a derailleur hanger that looks like it'll sorta fit. Take the frame and hanger to a machinist and say "I want to mount this part to this part so that these holes line up without welding and/or heating."

Pay the man a few hundred dollars and viola, you'll have a ridable frame again. Or, take that few hundred dollars and go buy yourself another equivalent frame and transfer the parts over.

And apologies, I'm not sure where I got that this bike was a mountain bike... was it mentioned above perhaps?

Thunder Horse

No apologies needed. Perhaps an association with Mongoose to MTB.
About the 5 mm, that is a point. Though I would hardly need to use an easier gear if I only ride on the flats. However, there will be an extra 5 mm gap between the derailleur and the spokes.

Thunder Horse

Thank you all for the great feedback. I have learnt a lot.
My friend emailed me to bring the bike over for look and see. He said, "the universal hanger looks great as a temporary on the road repair but would be a pain every time you wanted to remove the back wheel. The yellow bit repair looks a bit frail after drilling away most of what’s left. Give me a look, I have some similar types of repair parts..."
So when it stops raining over here, I will take the bike to my friend's place.
Will report back later.