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Chain falls off when rolling backwards

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Chain falls off when rolling backwards

Old 12-04-19, 06:34 PM
  #1  
trek330
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Chain falls off when rolling backwards

Is this normal?I have a triple shimano105 and if I back the bike up(not on it necesarily)like getting off an elevator the chain falls off the little front cog up front.Other than that the gears are well functioning and adjusted.Anything I can do about this?
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Old 12-05-19, 09:17 AM
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Is the chain slack in the "granny" (smallest) chainring? Try having the bike in one of the largest rear cogs when in the granny to keep the chain tighter. A sure cure is a chain watcher that physically keeps the chain from falling off of the smallest chainring. The Third Eye Chain Watcher and N-Gear's Jumpstop both work well and are relatively inexpensive
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Old 12-05-19, 09:32 AM
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The mentioned devices are meant to retain the chain during shifting when pedaling forward, not back pedaling. The little tabs/blocks reside on the upper half of the chainrings and back pedaling drop off starts at the ring's bottom half. But Dave does make a good point about the cog/ring combo employed when drop off happens. One more reason why riding in cross over combos is to be avoided. Andy
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Old 12-05-19, 10:04 AM
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Wouldn't a stiff link or gummed up pulley cause that?
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Old 12-05-19, 10:15 AM
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Originally Posted by wphamilton View Post
Wouldn't a stiff link or gummed up pulley cause that?
This. Also poor chain line, very worn chain or very very worn derailer can cause this
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Old 12-05-19, 10:29 AM
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When I shift from drive to reverse in my car while still rolling forward at 10 mph, bad things happen. What's wrong with the car?

Many if not most derailleur-equipped bikes will drop the chain in one or more gear combinations. Derailleur systems operate by changing the angle of approach of the chain at the point where it meets the sprocket or chainring. That's a controlled process pedaling forward and an uncontrolled process pedaling backward (or rolling the bike backward).

Moral: don't pedal backward and don't roll the bike backward---bikes aren't designed for that.
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Old 12-05-19, 12:11 PM
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Originally Posted by Trakhak View Post
Moral: don't pedal backward and don't roll the bike backward---bikes aren't designed for that.
Well, yeah, but all four of my 3x10 road bikes will allow indefinite backwards pedaling and rolling the bikes backwards without the chain dropping so it's not a universal problem. However, they in a middle gear and the chain has no slack. I expect the OP's bike is pretty cross chained when this occurs.
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Old 12-05-19, 12:18 PM
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Is rolling backward a common activity for you? To steal an idea from Vaudeville, stop rolling backwards.

But does this happen when you pedal backward? As a diagnostic, this issue may have been useful as it alerted you to poor chainline alignment.
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Old 12-05-19, 12:38 PM
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Originally Posted by HillRider View Post
Agreed. For example, all four of my 3x10 road bikes will allow indefinite backwards pedaling and rolling the bikes backwards without the chain dropping so it's not a universal problem. However, they in a middle gear and the chain has no slack. I expect the OP's bike is pretty cross chained when this occurs.
Edited to clarify that nothing in HillRider's post contradicts anything in my post.
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Old 12-05-19, 01:28 PM
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Seems like dropping the chains because of cross-chained on the small ring will drop off the outside, between the rings. OP gives me the impression that it's dropped to the inside, which would need a really bad chain-line to happen on the small ring and big cog (ie, not cross-chained).

So I wonder if his DR cage is just out of whack, or the hanger. Bent inwards.

ps, it would be a little silly IMO to insist on picking the bike up every time you want to move it backwards, out of fear of exceeding the design capability.
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Old 12-05-19, 04:32 PM
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Rolling a bike backwards, or back pedaling a chain, and having it come off is a good that something is wrong. It could be your dropout alignment.
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Old 12-05-19, 07:25 PM
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Originally Posted by Trakhak View Post
Edited to clarify that nothing in HillRider's post contradicts anything in my post.
It wasn't intended too as your statements were correct. I was just making the point that the problem isn't universal and that something in the OP's bike configuration is causing his specific problem. I think most of us expect he is badly cross chained or has a major chainline issue.
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Old 12-05-19, 08:14 PM
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Maybe I am a bit off topic, but what happens when there is not enough chain wrap up from the rear derailleur to keep the chain in place? If the chain is too slack it may drop off from play in the slack chain. JMHO. MH
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Old 12-06-19, 12:43 AM
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Something somewhere is sticking and possibly sticking just a bit. I'd check the freehub as well as the chain links and the derailleur pulleys.

Cheers
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Old 12-06-19, 02:26 AM
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When you roll a bike backwards it will pull the chain with it from the top, your crank will turn and on the bottom there is nothing guiding the chain. If in the big/big combination it will fall off on my bike and likely yours too. Moreover, when in this combination the pull of the rear derailleur will exacerbate the motion of the chain as it takes up the slack caused by the falling chain. In other words, once it starts falling you won't be able to stop it by moving the bike forward.
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