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I was cleaning the chain on my CX bike today, and while cleaning the rear derailleur I noticed the following: When moving the cage from one extreme to another, the cage body will rub against the derailleur (main?) body at one point somewhere around the middle point of its movement range.

Please see the linked video which will hopefully clarify my explanation: VIDEO

I don't think this is normal so I guess I would like a confirmation whether the derailleur is bent or not, or there is some other problem. It is a relatively new Shimano RD-5701 middle cage derailleur which has possibly received one abnormal knock when I was putting the bike into the trunk of my car.

The shifting is functioning pretty much OK except some difficulties at the two smallest cogs (I am using a 11-32 cassette), which I think are at least partly caused by improper adjustment of the derailleur and cabling, as the whole set is quite new so the cables and housing are definitely not yet worn in, but maybe this rubbing can be another cause?

I would be very grateful for any comments or suggestions.

  • one suggestion would be to cost up a new one, it might drive you to conclude that this part is sufficiently low cost that it is a no-brainer just to replace it if you think there's a problem. – PeteH Dec 6 '15 at 21:17
  • OK, here's the conclusion to the story. I put the chain back on to the bike and made some fine-adjustments to shifting. This kind of rubbing did not occur with the chain on. However, I was only able to ride for a very short distance, when going uphill and changing to the smallest gear (largest cog) the derailleur ended up in between the spokes. Apparently the derailleur hanger was bent and caused the failure to the derailleur. – nape Dec 12 '15 at 15:23
  • And for the initial question: I bought a new identical rear derailleur, and the rubbing which was present in the video did not occur with it without the chain installed, so presumably the derailleur was already bent slightly when taking the video. – nape Dec 12 '15 at 15:25
  • okay. Are you aware that a specific tool exists which will both tell you whether your hanger is bent, and will bend it back to true? The link to the Park Tools one is here, although I suspect other makes are available. But note there's nothing particularly fancy about this tool, you're essentially brute-forcing the hanger back into place. – PeteH Dec 12 '15 at 15:37
  • Yeah, I am aware of those tools, however I already bought a new dropout (my bike has sliding dropouts which enable both geared and single-speed use) as it was readily available locally. – nape Dec 12 '15 at 15:51
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I don't see any chain in the video. It (most) will do that with no chain. The spring is (hopefully) strong enough to pull an untethered derailleur into the cassette. Park Chain Length Sizing

Now the derailleur may also be bent but that is something different.

The rubbing in that video is only a problem if it rubs with the chain installed.

  • OK, thanks for the answer and I see your point. I'll check again with a chain installed. – nape Dec 6 '15 at 18:41

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