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  1. #1
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    Front chain keeps jumping off

    The chain keeps jumping off the front gears. I thought this was a problem specific to my older Walmart bike, but it seems to exist on my newer Diamond Back as well. Is this something common to all bikes? What's the cure?

    (But, to DB's credit, it's FAAAAR easier getting the chain back on as it doesn't pinch itself between the sprockets and frame.)

  2. #2
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    When does this happen?

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    When I bicycle.

    I haven't really noticed the exact situations it tends to happen in as my riding is "subconscious"/unnoticed, but it probably happens when I'm down shifting. I thought it was funny it never happened on the back gears but it seems to happen fairly often on the fronts.

  4. #4
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by swbluto View Post
    When I bicycle.

    I haven't really noticed the exact situations it tends to happen in as my riding is "subconscious"/unnoticed, but it probably happens when I'm down shifting. I thought it was funny it never happened on the back gears but it seems to happen fairly often on the fronts.
    You need to pay attention to how it comes off. There are several ways of knocking a chain off the crank and they have different causes. For example, if the chain falls off when you shift up to higher gears (larger chainwheel) there is one remedy for that. If it falls off when you shift to lower gears, there is a different remedy for that. If it gets stuck between the chainstay and the wheel, there's even a different fix for that. We can't help without information. Next time it happens, pay attention to what you were doing before it happened, then tell us. We can help then.
    Stuart Black
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    cyccommute, I don't mean to hijack this thread, but what's the remedy when:

    Going from middle to largest chainring on a triple (Ultegra FD, 105 RD long cage, 11-25 9 speed cassette, Tiagra shifters, many miles on everything), while on the smallest (fastest) cog in the rear, the chain comes off the ring to the outside, pedaling freezes up. I don't think the adjustment is the problem: I've checked all the stop screws and they look okay, things shift perfectly fine when on the stand. Happens when I'm cranking hard and shifting forcefully.

    The crankset is pretty old and I suspect biggest chainring is a bit warped (though visually it still looks okay).

  6. #6
    Neophyte Caribou2001's Avatar
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    Quote Originally Posted by rushibhai View Post
    cyccommute, I don't mean to hijack this thread
    +1... I feel the same myself... have a chain popping off front chain-ring issue, but it seems best to keep it in this thread (maybe it'll help when down the road someone is searching for an answer to have all the remedies in one place...?)

    In my case, the chain pops off the middle chain-ring under torque.... it hops right past the inner chain-ring and I typically have to come to a full stop and manually re-mount the chain.


    I found this thread, Middle Chain Ring Problems which suggestes the MCR is worn out, but, stipulates that you should be able to get 15-20,000 miles on a chain-ring... I bought my 2001 touring bike used, and the seller said it had maybe 4000 km on it, so what would I look for on the chain-ring to determine it's wear?

    I am getting the chain/cassette replaced, should I just get the MCR replaced at the same time, or see if the new chain fixes the problem?

    TIA, and sorry for the hijack!
    It's that time of year again... I'm trying to get some donations for the June 2010 Ride 4 Heart any donations of $1 or more are greatly appreciated!!! (click the blue link text to donate for me). If I reach my funding goal I'll make it a full century by repeating the upper loop an extra time.

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    Senior Member daintonj's Avatar
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    Quote Originally Posted by rushibhai View Post
    Happens when I'm cranking hard and shifting forcefully.
    Let me fix that for you.

    'When I'm putting my drivetrain under undue pressure through poor technique'

    Don't pedal hard while shifting. Think about what shifting is as it's not a magical process, it is a mechanical contrivance which can be understood. As you're pedalling you are putting the chain into a tensioned state the harder you are pedalling the greater the tension, the higher the tension the more force is needed to get the chain to extend past the point where the teeth of the cog are fully meshed in the chain links. You've just tried change chain ring with a heavily tensioned moving chain which is somehow now expected to glide onto a different and quite often largely different sized chain ring with no problem, this is unreasonable.

  8. #8
    Senior Member DannoXYZ's Avatar
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    Yeah, the rear-derailleur shifts the un-tensioned side of the chain. So no matter how much force you're applying to the pedals, the rear will be able to shift.

    However, the front-derailleur shifts the top tensioned side of the chain. If you shift while applying a lot of force, the FD won't be able to bend the chain very much. Maybe just enough to push it off the current chainring, but not enough to put it onto the next one.

  9. #9
    Senior Member Joshua A.C. New's Avatar
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    Yeah, the rear-derailleur shifts the un-tensioned side of the chain. So no matter how much force you're applying to the pedals, the rear will be able to shift.
    Danno, the only thing is, when you're putting a lot of tension on the chain, it makes horrible popping sounds as the chain gets in line. I think it's bad news to shift under that much tension. It won't derail, but I do think it puts undue stress on the cassette. It's often accompanied by manhandling the shifter, too. Force, as a rule, does not make machines run more smoothly.
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    To summarize what's been said and add a bit more, don't shift the front while under load. Soft pedal for a split second while the shift completes then go back to cranking. You won't lose the race

    If while shifting correctly your chain pops off to the outside of the big chainring, you need to adjust your high stop screw. Back it off 1/4-1/2 turn and try again.

    If you while shifting correctly your chain pops off to the inside of the little chainring, you need to adjust your low stop screw. Screw it tighter by 1/4-1/2 turn and try again. If you have to turn the screw in so far that you get rubbing in the little/big combo, there are chain catchers that mount to the seattube that will help correct the problem. Third Eye makes one.

    If you while shifting correctly your chain misses the middle ring, you need to adjust your cable tension.

  11. #11
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by rushibhai View Post
    cyccommute, I don't mean to hijack this thread, but what's the remedy when:

    Going from middle to largest chainring on a triple (Ultegra FD, 105 RD long cage, 11-25 9 speed cassette, Tiagra shifters, many miles on everything), while on the smallest (fastest) cog in the rear, the chain comes off the ring to the outside, pedaling freezes up. I don't think the adjustment is the problem: I've checked all the stop screws and they look okay, things shift perfectly fine when on the stand. Happens when I'm cranking hard and shifting forcefully.

    The crankset is pretty old and I suspect biggest chainring is a bit warped (though visually it still looks okay).
    This is a limit screw problem. The derailer is moving the chain too far outboard and knocking the chain off the crank. Park Tools will help you adjust it. The key to proper adjustment is to adjust the outer limit screw so that it won't rub but not so far outboard so that the chain can be knocked off.

    It is possible to get the chain back on without stopping for this kind of problem. Click the front derailer back one step (towards the inside) while pedaling - lightly - and the chain can reengage. It takes a little finesse but you can do it with practice. However fix the problem
    Stuart Black
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  12. #12
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by Caribou2001 View Post
    +1... I feel the same myself... have a chain popping off front chain-ring issue, but it seems best to keep it in this thread (maybe it'll help when down the road someone is searching for an answer to have all the remedies in one place...?)

    In my case, the chain pops off the middle chain-ring under torque.... it hops right past the inner chain-ring and I typically have to come to a full stop and manually re-mount the chain.


    I found this thread, Middle Chain Ring Problems which suggestes the MCR is worn out, but, stipulates that you should be able to get 15-20,000 miles on a chain-ring... I bought my 2001 touring bike used, and the seller said it had maybe 4000 km on it, so what would I look for on the chain-ring to determine it's wear?

    I am getting the chain/cassette replaced, should I just get the MCR replaced at the same time, or see if the new chain fixes the problem?

    TIA, and sorry for the hijack!

    Yours could be a couple of issues. A loose cable will allow the derailer to move too far inboard as you shift and skip over the middle ring. Your inner limit screw may also be misadjusted which allows the derailer to move too far inboard also. Look at Park (above) for the fix.

    By then way, it's best to start with cables on just about all derailer problems. Seldom does the limit screw need to be, well, screwed with if it's working properly. For both you and rushibhai, however, there is a problem with the limit screws.
    Stuart Black
    Solo Without Pie. The search for pie in the Midwest.
    Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
    Days of Wineless Roads. Bed and Breakfasting along the KATY
    Twisting Down the Alley. Misadventures in tornado alley.
    An Good Ol' Fashion Appalachian Butt Whoopin'.

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    Quote Originally Posted by daintonj View Post
    You've just tried change chain ring with a heavily tensioned moving chain which is somehow now expected to glide onto a different and quite often largely different sized chain ring with no problem, this is unreasonable.
    Makes sense. Thanks.

  14. #14
    Neophyte Caribou2001's Avatar
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    Quote Originally Posted by cyccommute View Post
    A loose cable will allow the derailer to move too far inboard as you shift and skip over the middle ring. Your inner limit screw may also be misadjusted which allows the derailer to move too far inboard also.
    Thanks for the reply. I'm pretty sure it has nothing to do with the derailer, because it happens not when shifting but only when applying torque. When I bought the bike I spent an hour adjusting the front derailer and while I admit I might not have done a perfect job, the problem I'm talking about happens when the derailer is perfectly straddling the chain.
    It's that time of year again... I'm trying to get some donations for the June 2010 Ride 4 Heart any donations of $1 or more are greatly appreciated!!! (click the blue link text to donate for me). If I reach my funding goal I'll make it a full century by repeating the upper loop an extra time.

  15. #15
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by Caribou2001 View Post
    Thanks for the reply. I'm pretty sure it has nothing to do with the derailer, because it happens not when shifting but only when applying torque. When I bought the bike I spent an hour adjusting the front derailer and while I admit I might not have done a perfect job, the problem I'm talking about happens when the derailer is perfectly straddling the chain.
    Think of the derailer as a 'chain keeper' If adjusted properly, the derailer won't let the chain fall off the chainring. Granted under high torque lots of weird stuff can happen but I'd bet that you derailer isn't moving far enough out even in the middle ring. Do you get chain rub in the middle? If so, the derailer is doing its derailer job but not when you want it. You may want to check the alignment of the derailer too. If the nose is too far out and the tail too far in, it could be knocking the chain off.
    Stuart Black
    Solo Without Pie. The search for pie in the Midwest.
    Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
    Days of Wineless Roads. Bed and Breakfasting along the KATY
    Twisting Down the Alley. Misadventures in tornado alley.
    An Good Ol' Fashion Appalachian Butt Whoopin'.

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    How clean and lubed is your chain? A dirty and or dry chain will cause this as well, if I'm not mistaken. And if I am mistaken, I'm sure someone will let me know about it too.

  17. #17
    Senior Member daintonj's Avatar
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    Quote Originally Posted by danny124 View Post
    How clean and lubed is your chain? A dirty and or dry chain will cause this as well, if I'm not mistaken. And if I am mistaken, I'm sure someone will let me know about it too.
    You're mistaken unless you can think of a reasonable argument for why a dirty or dry chain could cause this behaviour. A chain would have to be so dirty with solid crud that the teeth would not mesh to even get close to this, so possible but very unlikely.

  18. #18
    Neophyte Caribou2001's Avatar
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    Quote Originally Posted by cyccommute View Post
    Think of the derailer as a 'chain keeper' If adjusted properly, the derailer won't let the chain fall off the chainring. Granted under high torque lots of weird stuff can happen but I'd bet that you derailer isn't moving far enough out even in the middle ring. Do you get chain rub in the middle? If so, the derailer is doing its derailer job but not when you want it. You may want to check the alignment of the derailer too. If the nose is too far out and the tail too far in, it could be knocking the chain off.
    Well, as I said, I'm no wrench so I'm sure the derailer wasn't perfectly adjusted by me when I bought the bike. However, I just got it back from the LBS who replaced the cassette & chain, and it seems they tuned-up the bike too, although the only labour charge they gave me was for a drive-train-cleaning ($30). They even re-taped my bars (my LBS rocks). If I have any trouble with the chainring in the next weeks then I'm just going to get a new centre chain ring.... (I think the prior chain was asked to do too much, and probably took the centre chainring down with it, is my guess, even though I hear they can go 15,000 miles)

    S'ok - I plan to keep the new chain well-lubed, and replace it as needed .. what, every 5,000 km? better to replace the chain too often than have an old chain kill the cassette and/or chainring!

    Thanks again!
    It's that time of year again... I'm trying to get some donations for the June 2010 Ride 4 Heart any donations of $1 or more are greatly appreciated!!! (click the blue link text to donate for me). If I reach my funding goal I'll make it a full century by repeating the upper loop an extra time.

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