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New chain skipping on rear derailleur

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New chain skipping on rear derailleur

Old 05-23-16, 06:14 AM
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olie777
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New chain skipping on rear derailleur

Hi,

I have recently been buying and selling bikes, and am so quite new to the whole bike repair scene. I bought a specialized allez early 2000's model and it was all running fine but the chain snapped on it. So I have bought a new chain and am trying to fit it however I have observed that with the new chain the chain is skipping on and off the first derailleur every couple of teeth. It seems the chain moves to the right side of the first derailleur sprocket-cog-thing each time as it skips. Is there anything I can adjust or bend or take a hammer to to deal with this?

Cheers, Oliver
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Old 05-23-16, 07:00 AM
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Hard to tell from your description but probably need a new cassette/freewheel to match the new chain.
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Old 05-23-16, 07:07 AM
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Sounds like the chain is running off the side of the lower pulley. Not too uncommon especially with worn pulleys and cross chaining. Andy.
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Old 05-23-16, 07:09 AM
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Every couple of teeth or every couple of crank rotations?

That sounds like a tight link to me which happens a lot with a new chain. Try turning the crank backwards while watching where the chain exits the derailleur. If that's the case you'll be able to spot it right away. Loosen up that link a skosh and you'll be good-to-go.
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Old 05-23-16, 07:23 AM
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All of the above. Most likely are a tight link on the new chain where you joined the chain together, less likely if you used a master link. But RG has it right: suspend
the bike and slowly turn the crank while watching the chain go through the RD. OTOH if the problem happens while riding, ie chain under some torque then new chain/
worn cassette is the likely culprit. Generally cassettes last two chains. Worn idler pulleys possible but it generally takes a lot of riding to do that, depends on how
they look, should have relatively square teeth. Also top pulley should 'float' sideways on its bearing, but the bottom pulley does not, if inadvertently reversed
somehow it might cause a problem.
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Old 05-23-16, 07:37 AM
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Thanks for all of your replies, the chain skips throughout all links, and around one in every three or four links. Hard to explain, but it seems the chain is running too far right to be caught by the derailleur sprocket/cog then the chain ends up on top of the teeth then seats back again, I've attached a video here: https://vid.me/Qxor

Maybe its something to do with the alignment of the rear derailleur? Or the rear derailleur sprocket is sat too far left? The chain feeds back smoothly when pedalled backwards, only skips on the first sprocket on the rear derailleur when the chain is fed from the front derailleur.

Cheers for your advice, my terminology isn't so great but hopefully you guys can help me out

Oliver
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Old 05-23-16, 07:41 AM
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Looks like the derailleur is out of adjustment.
What model derailleur ? What model shifters ?
How many cogs on the rear wheel ?

Assuming it's an indexed drivetrain (the shifter "clicks" into each gear), then all the parts need to be compatible, and the derailleur needs to be setup correctly,

It appears the derailleur is set up in between cogs, meaning that when the shifter is in "gear 4", the derailleur is in "gear 4 1/2"

The barrel adjuster on the back of the derailleur is used to fine tune adjustment.

Look up some videos on how to set up the rear derailleur.

Also, if the hanger, the tab on the frame that the derailleur screws into, got bent at some point, that will lead to bad shifting, and needs to be fixed (bent back, or replaced). Looks like an aluminum frame, which suggests it has a replaceable hanger.
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Old 05-23-16, 03:01 PM
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Originally Posted by olie777 View Post
Is there anything I can adjust or bend or take a hammer to to deal with this?

Cheers, Oliver
Put the hammer down and move slowly away from the bike....
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Old 05-23-16, 04:18 PM
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Bike is upside-down in the video. RDs aren't under any obligation to run smoothly when you do that.
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Old 05-23-16, 07:57 PM
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It's not skipping on the upper pulley, only the lower, which makes suspect the lower pulley is binding and not turning freely.
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Old 05-23-16, 10:21 PM
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Originally Posted by Davet View Post
It's not skipping on the upper pulley, only the lower, which makes suspect the lower pulley is binding and not turning freely.
Or the pulley teeth are well worn. Or the hanger/cage is really bent, or the chain has stiff links/lube, or some massive cross chaining angle is at play, or... But I will say that the OP hasn't yet really assessed the state of the system in a way that many possibilities can be eliminated. Like many problem one must go through the various possibilities to filter out the static. Andy
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