Okay, why does my chain fall off if I backpedal when stopped?
04-06-12, 09:59 AM
#1
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Okay, why does my chain fall off if I backpedal when stopped?
This just drives me nuts, as when I am parked and just checking the chain and rings and derailleurs, if I back-pedal, the chain comes off the drive gear and ends up stuck in the front derailleur...what gives?
04-06-12, 10:13 AM
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Poor chainline?
04-06-12, 10:21 AM
#4
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#1, Don't back pedal..
derailleur guide pulley has to be dead under the cog, or it pulls the chain off. .
pick up the back wheel and pedal forward..
Note: another IGH advantage..
derailleur guide pulley has to be dead under the cog, or it pulls the chain off. .
pick up the back wheel and pedal forward..
Note: another IGH advantage..
04-06-12, 10:39 AM
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"B" ajustment not properly adjusted, not taking up enough slack in the chain.
04-06-12, 12:57 PM
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I'd vote for a bent RD. Or just a high chain angle.
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04-06-12, 01:09 PM
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- Check rear hanger alignment against a properly dished wheel that is installed centered between the stays.
- Clean and thoroughly lube chain.
- Make sure chain is correct length to begin with.
- Clean gunk off of chain rings, cogs and pulleys.
- Clean out pulley bearings so they are free of debris and fibers. (Stopped pulley is bad news...)
- Make sure you have correct size bottom bracket installed to avoid poor chain line.
- Get derailleurs properly adjusted - tune up so to speak.
=8-)
- Clean and thoroughly lube chain.
- Make sure chain is correct length to begin with.
- Clean gunk off of chain rings, cogs and pulleys.
- Clean out pulley bearings so they are free of debris and fibers. (Stopped pulley is bad news...)
- Make sure you have correct size bottom bracket installed to avoid poor chain line.
- Get derailleurs properly adjusted - tune up so to speak.
=8-)
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Disclaimer:
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5000+ wheels built since 1984...
Disclaimer:
1. I do not claim to be an expert in bicycle mechanics despite my experience.
2. I like anyone will comment in other areas.
3. I do not own the preexisting concepts of DISH and ERD.
4. I will provide information as I always have to others that I believe will help them protect themselves from unscrupulous mechanics.
5. My all time favorite book is:
Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life
04-06-12, 01:21 PM
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You know, I have been told before to "just don't pedal backwards" in regards to a chain falling off or not being smooth when pedaling backwards however I would say that a well tuned bike should be able to be pedaled backwards whereas a bike that is slightly out of tune might work okay but when pedaled backwards, might have problems. So even if the bike is working "okay" in normal use but when pedaled backwards, the chain falls off then I would say that the bike still isn't in proper tune state yet.
That is just me being anal about how well the bike is tuned up. And for all I know, there are bikes out there that just can't be pedaled backwards without things happening to them.
That is just me being anal about how well the bike is tuned up. And for all I know, there are bikes out there that just can't be pedaled backwards without things happening to them.
Last edited by bobotech; 04-06-12 at 01:40 PM.
04-06-12, 01:42 PM
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Sounds like your chain is falling off the front, yes? Rear derailleur adjustment won't fix that. Common culprits: worn out or really gunked up chain, worn out cogs, derailleur adjustment. Try to recreate the chain dropping while off the bike and watch what happens.
04-06-12, 03:00 PM
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^^^ The right answer.
Very unlikely to have anything to do with the rear derailleur adjustment, alignment, condition, etc. if the chain is falling off the front of the chainring, and "just don't pedal backwards" is just stupid. A well tuned bike should be able to be pedaled backwards in any gear combination.
Very unlikely to have anything to do with the rear derailleur adjustment, alignment, condition, etc. if the chain is falling off the front of the chainring, and "just don't pedal backwards" is just stupid. A well tuned bike should be able to be pedaled backwards in any gear combination.
Last edited by Stealthammer; 04-06-12 at 03:06 PM.
04-06-12, 03:30 PM
#12
Mechanic/Tourist
When backpedaling the chain is leaving the bottom derailleur pulley and being pulled toward the lower part of the front chainwheel. If the rear derailleur is in a larger cog (closer to frame center) and the chain is on the large chainwheel (farthest from frame center) there is a significant angle between front and rear. The only tension is that produced by the rear derailleur pulley springs and there is nothing to help guide the chain onto the bottom of the chainwheel. Under those conditions the chain could easily unship from the chainwheel. If the chain weaves a little or if the bike is leaning to the left it could happen even more easily.
However, one should be able to backpedal when stopped in order to have the pedals in a good position for starting up again. The cure is to pre-shift to a better chainline gear combo before stopping.
Last edited by cny-bikeman; 04-06-12 at 03:46 PM.
04-06-12, 03:40 PM
#13
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I assumed (wrongly) that the chain fell off the back. If it's on the front, I'd check chainline first.
04-06-12, 03:46 PM
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Yep, you are correct. A bent derailleur or out of alignment will cause the chain to lift off the bottom of the front chainring. I was erroneously assuming that drivetrain was otherwise well tuned. My bad. Too many distractions..... 
Last edited by Stealthammer; 04-06-12 at 03:52 PM.
04-06-12, 05:39 PM
#16
Mechanic/Tourist
No problem, but well tuned or not, if there is a large angle between front and rear it is not out of bounds for chain to unship when backpedaled.
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