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Old 04-10-10, 09:14 PM   #1
moose8
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Chain fell off rear derailleur - mean anything?

Today I was riding my bike with a mid-90s campy mirage rear derailleur - I was pedaling quite hard, probably going around 23mph at the time, when the chain skipped off on off the little wheels on the rear derailleur and kind of jammed in it. I've had many chains fall off before, but it's always been upfront. Does this signify something might be worn out or something?
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Old 04-10-10, 09:44 PM   #2
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First set limiting adjusters then make sure hub spins freely for starters
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Old 04-10-10, 10:00 PM   #3
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Terminology fail.
The cogs that make up your cassette (unless you have a freewheel instead) are not a part of your derailleur. The only "cogs" that are a part of the derailleur are the jockey wheels, and unless the cage exploded, the chain isn't falling off of them.
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Old 04-10-10, 10:17 PM   #4
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Terminology fail.
The cogs that make up your cassette (unless you have a freewheel instead) are not a part of your derailleur. The only "cogs" that are a part of the derailleur are the jockey wheels, and unless the cage exploded, the chain isn't falling off of them.
Correct on terminology failure! I ride a bike a lot, yet I can never seem remember any of the right terms. What seemed so weird to me was that it fell off the jockey wheels - nothing appeared to break, but the chain was jammed between the two little jockey wheels, and the tension went out of the rear derailleur (so it was like it is when no chain is on it). It happened right after I started pedaling really hard, which also made me a little sketched out. That's why I'm wondering if it means anything other than I just had a weird chain failure that hasn't happened before and hopefully won't happen again.

Everything seems to be spinning fine.
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Old 04-10-10, 11:15 PM   #5
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I'm gonna need to see a picture, because the way you are describing it, the derailleur spring broke or possibly the jockey wheels are so worn they can't keep the chain in place anymore. I'd take it to the LBS and have them examine your derailleur thoroughly.
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Old 04-11-10, 07:00 AM   #6
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Attached Images
File Type: jpg derailler1..jpg (61.9 KB, 58 views)
File Type: jpg derailler2..jpg (50.8 KB, 45 views)
File Type: jpg derailler3..jpg (45.0 KB, 48 views)
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Old 04-11-10, 11:47 AM   #7
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It looks like the chain is threaded through the jockey wheels properly, and from what I can see in the pictures, the wheels don't look terribly worn. However, reviewing what you said, it is possible that maybe the top jockey wheel jammed briefly, but the chain continued to feed into the jockey wheels, causing a backup of chain that jammed between the two jockey wheels. If that is the case, is it possible to get replacement jockey wheels for that derailleur. It also might just need a thorough cleaning. If you have an LBS near you, I would take it in, and explain as best you can what happened, and they will likely take a look at the derailleur and determine at least if anything is broken or excessively worn.
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Old 04-11-10, 03:00 PM   #8
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Thanks! I gave it a very thorough cleaning not very long ago - doesn't take many puddles to make the bike filthy again.
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Old 04-11-10, 03:33 PM   #9
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I've been on rides where I've found eucalyptus bark wrapped around the pulleys. They seem to collect a lot of stuff very quickly, which is why they get a wipe-down along with my chain after every ride.
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Old 04-11-10, 03:52 PM   #10
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if this only occured once I suspect it might simply be a case of the chain and pulleys being a bit dirty to keep up with your pedaling pace. also I agree with deep_sky it may be something was just kicked up into the chain or RD causing it. it is possible too that you have mildy stiff link and again the slack between the bottom of the chainwheel and the iddler pully was just slack enough to cause a mild disturbance
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Old 04-11-10, 05:38 PM   #11
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Mid 90's Campy is not meant to go 23 mph and higher. SLOW DOWN.
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Old 04-12-10, 02:07 AM   #12
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Sounds weird... I'd have a good go at trying to replicate the problem on a stand, and if you can't make it happen again just put it down to some random crap fouling your derailleur for a sec.
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Old 04-12-10, 06:27 AM   #13
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Mid 90's Campy is not meant to go 23 mph and higher. SLOW DOWN.
Really? Why? I do usually go much slower on it, but I was pushing it this time to go the same speed as traffic and that is when the failure occurred. I just pulled off to the right and was fine. I certainly don't want to do anything that could result in gear failure that would be dangerous.
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Old 04-12-10, 08:43 AM   #14
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Quote:
Originally Posted by moose8 View Post
Today I was riding my bike with a mid-90s campy mirage rear derailleur - I was pedaling quite hard, probably going around 23mph at the time, when the chain skipped off on off the little wheels on the rear derailleur and kind of jammed in it. I've had many chains fall off before, but it's always been upfront. Does this signify something might be worn out or something?
You may have gotten smutz in the derailer or you may have a jockey wheel that need lubrication. I'd check to see if the jockey wheels turn freely without the chain on them.

You may want to check for a stiff chain link too. Your chain looks a but crusty.
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Old 04-12-10, 10:29 AM   #15
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Quote:
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Mid 90's Campy is not meant to go 23 mph and higher. SLOW DOWN.
Really? Why? I do usually go much slower on it, but I was pushing it this time to go the same speed as traffic and that is when the failure occurred. I just pulled off to the right and was fine. I certainly don't want to do anything that could result in gear failure that would be dangerous.
No, not really. He's yanking your chain.



I know there's a pun in there somewhere.
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Old 04-12-10, 10:34 AM   #16
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the chain was jammed between the two little jockey wheels, and the tension went out of the rear derailleur (so it was like it is when no chain is on it).
I find that very strange. With the chain jammed in the RD, the chain should have been pulled tight against whatever cog it was engaging when you tried to pedal. The bike would freewheel, but you wouldn't be able to turn the crank forward at all. Are you sure that it didn't jump off the front rings?

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Thanks! I gave it a very thorough cleaning not very long ago
AHA! I bet you washed all the lube out of the pulley bearings, causing one or more to jam. Can you tell if they turn freely (you'll have to disengage the chain).
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Old 04-12-10, 10:50 AM   #17
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Today I was riding my bike with a mid-90s campy mirage rear derailleur - I was pedaling quite hard, probably going around 23mph at the time, when the chain skipped off on off the little wheels on the rear derailleur and kind of jammed in it. I've had many chains fall off before, but it's always been upfront. Does this signify something might be worn out or something?
what gear combo were you in?

a too short bottom bracket spindle might cause the chain slipping off the guide pulley (the top one when the derailer is installed with a chain in it) if the bike is being ridden in the small chainring up front and the small sprocket in the rear.

Have you had any work done that might have changed your chainline? bottom bracket or wheel, or crankset or cassette replacement?
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Old 04-12-10, 10:52 AM   #18
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what gear combo were you in?

a too short bottom bracket spindle might cause the chain slipping off the guide pulley (the top one when the derailer is installed with a chain in it) if the bike is being ridden in the small chainring up front and the small sprocket in the rear.

Have you had any work done that might have changed your chainline? bottom bracket or wheel, or crankset or cassette replacement?
correction: the chain slips off the tension pulley (bottom wheel), not the guide pulley when in the small-small combo.
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Old 04-12-10, 11:26 AM   #19
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I don't get a lot of the humor on these forums. Anyway, I took the whole bike apart and put it back together a few months ago, so entirely possible I screwed something up. I did take it to bikeshop for a tuneup after though to make sure I hadn't done anything too stupid, and they said it seemed fine. There does appear to be a really stiff link in the chain, looks like it's kind of pinched in, which I probably caused last
time I took the chain off, so I'll try to fix that. I think the chain was on the smallest cog on the back and the biggest ring on the front when it happened, or at least when I pulled over and unclipped to look at it. It could have been the smaller ring up front though - I'm positive it was the small cog in the back. Thanks to everyone who replied - it helps to learn what questions I need to be asking.
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Old 04-13-10, 11:03 PM   #20
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I don't get a lot of the humor on these forums. Anyway, I took the whole bike apart and put it back together a few months ago, so entirely possible I screwed something up. I did take it to bikeshop for a tuneup after though to make sure I hadn't done anything too stupid, and they said it seemed fine. There does appear to be a really stiff link in the chain, looks like it's kind of pinched in, which I probably caused last
time I took the chain off, so I'll try to fix that. I think the chain was on the smallest cog on the back and the biggest ring on the front when it happened, or at least when I pulled over and unclipped to look at it. It could have been the smaller ring up front though - I'm positive it was the small cog in the back. Thanks to everyone who replied - it helps to learn what questions I need to be asking.
interesting. did you remove the bottom bracket spindle?
what's the clearance between the small chainring and the chainstay?
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