# 105 / Ultegra Rear Deraileur snapping hanger



## tripyrenees (Apr 4, 2010)

Hi
I have had a second failure of my rear derailleur in less than 6 months. This has happened on separate bikes, one with 105 and one with Ultegra. In fact I have seen this 3 times in the past 6 months with a clients bike (Trek) having exactly the same problem.

At low speed changing (probably down, not sure) the rear derailleur hooks back and is flung in the direction of the wheel rotation, snapping clean the rear hanger and lodging itself into the rear spokes, jamming the rear wheel solid. The derailleur itself is totally bent out of shape and I have had the Ultegra snap the swing arm casting the jocky wheels off into the street.

In the three instances I have seen (one of them to myself) it happens within the first kilometer of the ride, at low speed. It is very scary, dangerous and basically is a replacement of the hanger, derailleur and in some cases bends the frame. It has also bent the axle on the rear wheel.

Has anyone had a similar experience and if so what causes it. The most recent was this morning on a brand new bike, so new chain, new cassette, new derailleur etc etc. 4th time out on the road and working perfectly - then Wham, total disaster.

Would appreciate any thoughts on this issue as it is becoming more common that I thought.


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## PJ352 (Dec 5, 2007)

From what you describe I'd say it's occuring because the low limit (or adjustment) screw isn't adjusted properly, allowing the RD to over shoot the largest cog then being caught (and rotated with) the rear wheel spokes.

http://techdocs.shimano.com/media/t...00-5501/SI-5TK0D-En_v1_m56577569830603908.pdf


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## tripyrenees (Apr 4, 2010)

It happened mid cassette so not reaching the limits.

Somehow the chain has got caught or stuck within the derailleur and caused it to be swung over as the chain goes round. It ended up in the spokes after the hanger had snapped. 

I am just trying to figure out why the chain would get stuck.


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## PJ352 (Dec 5, 2007)

tripyrenees said:


> It happened mid cassette so not reaching the limits.
> 
> Somehow the chain has got caught or stuck within the derailleur and caused it to be swung over as the chain goes round. It ended up in the spokes after the hanger had snapped.
> 
> I am just trying to figure out why the chain would get stuck.


Ah, in that case I'd check for a loose/ protruding pin (that would explain the chain getting caught in the RD cage) and/ or a stiff link, although in the case of the latter I'd think if the link were that stiff you'd already know about it.


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## andulong (Nov 23, 2006)

How are you joining your chain? Maybe the masterlink is hanging up.


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