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Old 01-16-13, 11:47 AM   #1
dprayvd
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rear derailleur issue...

...



Wasn't doing anything I havn't done a zillion times previous. The wheel and chain survived, and the hanger was mildly bent.

So, waitin' on an ebay 4500 @ $32.
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Old 01-16-13, 12:05 PM   #2
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10:1, this was a simple case of a mis-adjusted inner limit screw allowing the RD to engage a spoke. You may find evidence of this in the form of a bent or nicked spoke. Many people think of limits as set and forget, and in a perfect world they are. However the adjustment changes if the hanger is bent (always inward). Simple banging around, such as a fall on the right side can push the hanger in leading to the limit adjustment being too far inboard.

The other possibility is that the "B" screw was mis-adjusted so the upper pulley was too close to the cassette and engaged a sprocket (through the chain). This can push the RD back and in some cases break it off.
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Old 01-16-13, 01:02 PM   #3
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I wonder if the oft-maligned spoke protector AKA "dork disc" might have prevented this mishap?
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Old 01-16-13, 01:11 PM   #4
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Originally Posted by dsbrantjr View Post
I wonder if the oft-maligned spoke protector AKA "dork disc" might have prevented this mishap?
Yes, it very well might have, but even a spoke protector isn't an absolute guaranty. While I don't use one, I don't like to see them maligned as "dork discs" with the implication that only dorks use them. They aren't bulletproof, but unless you're someone very in tune with your bike there's a good chance that they might prevent an expensive repair.
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Old 01-16-13, 01:22 PM   #5
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dprayvd, you might want to check very carefully for nicked or otherwise damaged spokes.
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Old 01-16-13, 02:35 PM   #6
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I'm with FB: some low-limit creep...

limits move, I reset mine often enough, so I believe

...combined with flex during right-pedal power application while the rear wheel crossed the gutter-pan to sidewalk transition (the kind on a corner as in ADA-type access) on a steep-ish hill going slowly. And a weak low-count paired-spoke wheel. And weighin' 215. And of course being in first.

The frame's a big '08 7.5fx. It has large, wispy dropouts. They suck. Well, probably not for someone a stone or three less.

If I was going fast(er) I'm sure the wheel would have toasted. I'm getting a wheelset regardless. This set has lived it's life.

Wanna' see the corner? Its the NW one.
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Old 01-16-13, 02:35 PM   #7
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The spoke protecter on the wheel was minimal. More for the chain than the RD. In fact I left it on until it broke of its own accord.
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Old 01-16-13, 02:44 PM   #8
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I just realized I didn't describe fully: the mech got with the wheel and was facing/pointing/twisting very rearward when everybody was done.
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Old 01-19-13, 05:52 PM   #9
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Well, now that its back together here is what happened.
--a month or two back, a rear NDS spoke pulled loose its rimbed so I fitted a new spoke (actuall three since I had out the drilling things). One of these (a DS add) couldn't get an inboard cross without me getting into the fix further so I cheaped-out. Well, it got untensioned enough on that pedal-stroke to grab the upper-tip on the inboard RD cage. 32 buck mistake. Gahh!! I elected to tie&solder the lil'bastid rather than do the cross.

Don't Cheap-Out on the Drive Side!
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Old 01-19-13, 07:28 PM   #10
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Thought I'd add a side bar to this thread. 30, or so, years ago I had a spoke grab this deraillure and tear it in two. I had ridden to a club Winter maintaniance night. Only one other guy rode there so I was already on the Good List. On the way home i cut down a side street in the shadows and wacked a pothole so hard that both rims buckled. The spoke on the rear that then bowed out snagged my deraillure. The lower half stopped rotating around the freewheel when it hit the rack brace. Well I sat down and with my tools removed the lower half and made the bike rideable, as the tires almost but not quite blew out only removing the deraillure bits and straightening a couple of chain links was needed. A little bit bothered but also a bit proud that I was able to cycle on I rode home. Bumping with each wheels flat spot and the chain swinging to and fro, auto shifting a few times. But wouldn't you know it the other guy who had ridden to the workshop passed me by before I got home. needless to say my Good list points dropped. Here's the paper weight I've had on my desk since. Andy.
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