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Old 02-09-09, 11:14 PM   #1
ernok1923
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shifting gears lead to a mangled rear drop out: your diagnosis?

has anyone ever seen this happen?



hear's the story:

riding tonight with my friend and his bike starts to make some noise. i tell him it that it sounds like he isn't in gear (friction shifting). he agrees, gently starts to shift, and then we hear the crunching noise. he comes to a dead stop. we look and see what happened.

turns out, his derailleur is now pointing towards the sky and the rear drop out is now wide open.

does anyone have any ideas as to what may have happened? its a mid to late 80's peugeot if that helps. thanks.

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Old 02-09-09, 11:26 PM   #2
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Could be several things.

Incorrectly adjusted derailleur limit screws allowed the derailleur to contact the spokes.

Chain failure, bent chain, loose pin, caused chain to jam in the derailleur.

Neither one is uncommon.
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Old 02-10-09, 07:50 PM   #3
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Something like a stick or piece of wire that got picked up by the chain and run through the derailleur could cause this type of damage.

I once ran over a piece of coat-hanger wire lying on the road and it completely mangled a nearly new Ultegra 9-speed rear derailleur. Fortunately the rear dropout was unscathed. Ti is tough stuff.
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Old 02-10-09, 07:51 PM   #4
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Originally Posted by ernok1923 View Post
has anyone ever seen this happen?



hear's the story:

riding tonight with my friend and his bike starts to make some noise. i tell him it that it sounds like he isn't in gear (friction shifting). he agrees, gently starts to shift, and then we hear the crunching noise. he comes to a dead stop. we look and see what happened.

turns out, his derailleur is now pointing towards the sky and the rear drop out is now wide open.

does anyone have any ideas as to what may have happened? its a mid to late 80's peugeot if that helps. thanks.

This is usually the result of a maladjusted derailleur. It hits the spokes, gets caught, and you know the rest.

The good news is that your friend's frame is steel, with malleable dropouts. Your LBS should be able to straighten it out, although depending on the extent of the damage the derailleur may need to be replaced and/or the wheel repaired.
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Old 02-10-09, 08:03 PM   #5
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Yep, looks like derailleur-in-spokes.
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Old 02-10-09, 08:06 PM   #6
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And the dork disk saves the day! (well, the wheel, at least)
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Old 02-10-09, 09:41 PM   #7
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And this, kids, is why you want to learn to set your limit stops.

Yikes.
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Old 02-10-09, 09:48 PM   #8
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something else is wrong too. Why is the lower-run of the chain aimed down so low? Post a picture of the entire bike.
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Old 02-10-09, 09:52 PM   #9
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something else is wrong too. Why is the lower-run of the chain aimed down so low? Post a picture of the entire bike.
Maybe just because the derailleur is not taking up the slack in the chain anymore?
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Old 02-10-09, 10:36 PM   #10
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Another possibility: the chain may be too short for the largest cog/largest chainring combination.
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Old 02-10-09, 10:45 PM   #11
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it certainly caused the dork disk to crack...

aren't the dork disks there to prevent the derailer from getting sucked into the wheel?
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Old 02-11-09, 03:20 AM   #12
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it certainly caused the dork disk to crack...

aren't the dork disks there to prevent the derailer from getting sucked into the wheel?
Depends on the diameter of the dork disc, and the position of the part of the derailleur cage that's trying to get sucked in.

On that bike, it appears that the top guide pulley should be somewhat protected from going into the spokes, which is what would probably happen if the limit screw were set wrong. But if something like a stick got sucked into the bottom pulley, all bets are off. Or if something broke.
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Old 02-11-09, 04:32 AM   #13
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There appears to be a lot of wear in the slot of the non drive side dropout. If a similar amount of wear existed on the drive side, then its possible that the dropout failed. I would have expected to see more spoke damage if the derailleur was ripped back by the wheel.
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Old 02-11-09, 05:27 AM   #14
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Yep, derailleur into the spokes. Looks like he was going slow.
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Old 02-11-09, 05:32 AM   #15
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it certainly caused the dork disk to crack...

aren't the dork disks there to prevent the derailer from getting sucked into the wheel?
I thought they were just there to rattle around making annoying noise and look ugly till you take them off.
That is of course assuming derailer is properly adjusted thus totally making the disk useless.
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Old 02-11-09, 05:57 AM   #16
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I had the exact same thing happen to my son's MTB in the moments before a race. For him, the cause was that the upper pulley in the rear derailure failed causing the chain to stop dead.
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Old 02-11-09, 07:32 AM   #17
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Breakaway Derailleur hangers

I've seen a lot of derailleurs turned around like this at the bike shop I work at, the only difference is on older bikes the derailleur hanger is part of the frame and on newer bikes the derailleur hanger is a separate piece which attaches to the dropouts. The derailleur hanger is designed to be weaker than the frame and to break away if the derailleur takes a hit so that the frame is left unscathed. I agree that your friends derailleurs limit screw was to far out or his hanger was bent causing the derailleur to catch the spokes and turn around. Since your friends derailleur hanger is part of the dropout it damaged the frame (you might be able to bend it back but the frame will be at least slightly weakened).
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Old 02-11-09, 08:25 AM   #18
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The old derailleurs can get loose pivots and can get sloppy, This could be the problem. If the wheel is not grabbing the dropouts hard enough, and moved, this could cause it. If the derailleur hanger got bent and he did not know it (the most common problem) that could be the problem. If a washer was left off of a wheel that needed it for spacing that could cause it. If the wheel was switched and the limit screws were not readjusted that would do it too. Just not clamping the quick release tight enough after a flat might do it.

It does not have to be a poorly adjusted limit screw.

I have saved a frame that was bent that much, but it was a lot of work to get the dropouts just right. I had to hold it over a flat anvil and hammer it to get the dropout straight enough.
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Old 02-11-09, 12:35 PM   #19
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I had something similar happen to me during a solo tour about 20 miles from the nearest town. While shifting to the small ring, the bottom side of the chain had somehow gotten between the freewheel and the spokes and brought me to a quick stop. I never figured out exactly why it occured. The high-low limits of the derailer were set correctly. I took the chain off and it looked OK. I took the rear derailer off and bent the derailer hanger back with a large 10" adustable wrench (and I almost didn't bring it because I didn't think I'd need it ). Luckily my drop-out didn't open up like in your pic. I put the derailer back on - the cage pivot bushing was broke and it had a bit of play but it worked. I rode the rest of the tour that way.

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Old 02-11-09, 01:25 PM   #20
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All of the spokes look OK. If the derailleur had gotten into the spokes enough to do that much damage, some of the spokes would be badly damaged also.
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Old 02-11-09, 01:31 PM   #21
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All of the spokes look OK. If the derailleur had gotten into the spokes enough to do that much damage, some of the spokes would be badly damaged also.
+1

I don't see how this could be a derailleur being caught in the spokes since the spokes look fine. Something stopped the chain moving through the derailleur so the chain sucked the derailleur up, not the spokes.
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Old 02-11-09, 03:45 PM   #22
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I've seen this (and worse) happen from a tight link in the chain that refuses to go through the derailleur.

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