Advice req'd - rear mech wrecked and gear hanger bent

mr.b-campag · June 2015

As per the title,

Had just set off from my evening commute when I hit a drain (not very hard) and heard an almighty racket from my back wheel. I got off to find the rear mech (bought from someone on here but I guess that is another story) had gone up above the cassette. The cage (esp. towards the lower jockey wheel) had been prized open and the gear hanger is severely bent in towards the cassette (enough for it not to be able to turn).

I took it back to work and got the train home, but obviously it needs fixing up. It's an old-ish (about ten years) steel Simoncini audax frame. Can I just bend the rear mech hanger back into place with a suitable large (say) adjustable spanner? There is no where close to my work I would take the bike to and no way of getting it home really without riding it somehow. Any tips on this much appreciated.

Also any thoughts on what went wrong with the mech (an old mirage 9 speed)? It was making a bit of noise recently and obv. I should have checked it out earlier. Any ideas what I should have been looking for, for future reference?

Thanks for reading.

B

mercia_man · June 2015

It's a steel frame and you should with luck be able to bend the hanger back. I've done it with my steel touring bike when my Veloce rear mech jammed and went into the wheel. I took off the broken derailleur and used a big adjustable spanner to straighten the hanger so it was parallel to the smallest sprocket on cassette. Professional mechanics will use a special alignment tool but doing it by eye worked for me and indexing is fine. It was the second time I had straightened the hanger. The first time it got bent was in a fall

As for why these things happen, who knows? Could be a badly adjusted mech, a twig or stone getting caught up or a ham-fisted attempt to change gear quickly when suddenly faced with a steep hill.

mr.b-campag · July 2015

Thanks MM, that's what I thought but good to hear others have done it. Still don't know why it went like that, i wasn't changing gear or anything else - as u say, an act of god perhaps :-)

woolwich · July 2015

Agreed, this should be a reasonably straight forward repair.
I find a nice way to manipulate the hanger is by finding a suitable bolt with the correct thread. Screw into the hanger and use the bolt as your lever. I just find its a little gentler, dropouts are often softer than you may think.
Take extra care if the dropout design is the more traditional forward facing slot design. The bottom slot can get twisted by the hanger, this is often along the line of the adjustment screw hole where there is little metal.
Lastly, even if it does turns out to be knackered, replacement dropouts are cheap and replacement is pretty straightforward if you can find somebody local willing to take the job on.

keef66 · July 2015

I've done this on one of the kids' MTBs. (full sus with a steel rear end; weighs more than the Bismarck)

Rear mech into the spokes, ripped apart, hanger bent. (on taking out the rear wheel I found the axle had broken, which may have been the root cause of the whole thing)

Large adjustable spanner to lever the hanger straightish. New mech screwed in, scrutinised from behind to see how vertical the mech cage was sitting. Couple of further tweaks to get it dead vertical, refit, cable up and away we go!

mr.b-campag · July 2015

Thanks again everyone. I like the idea of using a screw as the lever. Back in the day I would have just popped out to my dad's garage and found one but now that I'm far from home that's not really an option. Anyone any idea what size screw I would need so I can pop down to a hardware story and get one?

Saying that, would using the (now destroyed) rear mech as a lever not amount to much the same thing?

woolwich · July 2015

Yes I forgot you had the old part, screw it in and give it a go.
For reference the thread is M10x1.

mr.b-campag · July 2015

Great, thanks very much woolwich

curium · July 2015

I have had my derailleur hanger straightened just 2 hours ago at Decathlon in Surrey Quays so it is possible. They even had a special jig that screws in where the derailleur is normally located and allows them to see when it is lined up with the frame.

I actually had a replacement hanger to fit at home and was only in Decathlon because my chain had come off on the ride to work and wrapped itself around the crank and wouldn't budge. I stopped at Decathlon hoping they would cut it off and replace it. The mechanic managed to free it, noticed the derailleur hanger was out of alignment, straightened it and re-indexed all the gears for £12.99

mr.b-campag · July 2015

Re. Decathlon. Thanks for the heads up. That sounds like great service. I'm at the Wharf so that would be one of the nearest places for me to get this done. I'll give it a go myself first though. The main danger with decathlon is not the price of the service but all the other stuff I'll probably buy if I go in there!

mr.b-campag · July 2015

Did it myself in the end. Good enough to get me home but needs some more adjustment. In the end I had to grab the dropout itself, it took a lot of work but I just about got there. Unfortunately I wasn't thinking straight after a day at the office and didn't put a cloth around the hanger.

This resulted in most of the paint coming off (which I'm not that fussed about on my commuter/trainer) and wrecking most of the thread on the hanger. There was a bit of thread left at the end so I reversed the mech in to create some new thread. The mech now goes in fine but doesn't really do up properly - any ideas for how to fix this - perhaps just some thread lock?

Advice req'd - rear mech wrecked and gear hanger bent

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