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The gears work fine across the whole cassette on the inner ring but all of a sudden the chain has stopped engaging with the upper jockey wheel when in the big ring and three largest (easiest) sprockets of the rear derailleur.

The jockey pulley looks out of position when this happens (almost horizontal to the lower tension pulley jockey wheel - the chain then simply isn't reaching the upper jockey wheel) and the chain makes an unholy racket with the drive train eventually seizing up entirely until I shift into smaller (harder) sprockets.

This seemed to occur straight after I removed then replaced the rear wheel, catching it a little on the brake pads as I did, which resulted in a bit of a clunky removal.

Is this likely to be the result of a bent, misaligned rear derailleur?

  • Is the wheel seated 100% straight into the rear dropouts? – Glenn Stevens Aug 31 '15 at 0:47
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    Most likely the wheel axle is not seated all the way into the dropouts. Another possibility is that you knocked loose one of the springs on the derailer, though in that case you'd probably have problems in other gears. – Daniel R Hicks Aug 31 '15 at 0:52
  • Yes, I've checked that and even removed and replaced it again to be sure - it is dead centre of the frame. – Kiver Aug 31 '15 at 0:53
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    You can check first by looking to see if something appears to be missing or out of place. Failing that, remove the rear wheel and slack the shift cable (shift into the highest gear). The derailleur should move all the way to the outside with some authority. Now, push it back towards the center (low gears), you should feel some resistance and when you release the pressure it should move back towards the high gears (outside) again. If it doesn't do that it's a good bet that a spring is loose or missing. – dlu Aug 31 '15 at 6:31
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    The spring that moves the derailer in/out has nothing to do with it. There is also a spring that forces the derailer forward on the pivot, and sometimes a third. You just have to look for a spring that's popped off its hook. – Daniel R Hicks Aug 31 '15 at 11:26
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It would help if you could post a photograph, but what I'm picturing from your description is that when you shift onto any of the three largest cogs in the back while you're on the large chainring the derailleur cage is pulled almost horizontal and the jockey wheel disengaged from the chain.

To me, this sounds like your chain is too short. Since chains don't magically shrink what I think happened was that when you put the wheel back on the bike you pulled it further back in the dropouts than its original position and now the chain has farther to go. So, I think all you would need to do is to move the wheel forward in the dropouts.

All of this assumes that you have horizontal dropouts, if you have vertical dropouts I'm completely wrong…

  • That makes perfect sense, thanks. However, I do have vertical dropouts :/ – Kiver Aug 31 '15 at 9:30
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Man handling the rear derailleur I discovered the jockey wheels were indeed in the wrong position as a result of the rear mechs pivot point having seized up. I can push it into the correct position and the chain engages the jockey wheel and runs normally but the mech isn't moving freely by itself. This means it isn't extending fully to run in the big ring - larger cog gear combinations. Given the difficulty in servicing the internals of the rear mech I'm planning to replace the whole unit.

As an interim measure in the short term I've used a generous dose of penetrating oil around the pivot and it's freed things up enough to get things working for now. I wouldn't give it too long before a new mech is needed though.

  • Lube the pivot and check for a weakened (broken?) spring! – Carel Sep 1 '15 at 14:35
  • Thanks Carel. As an interim measure I have indeed flooded the area as best I can with some penetrating oil and it has freed things up a little for now. While it's got things working in the short term I wouldn't give it too long before a new mechs needed. I think the springs are okay, certainly nothings broken. – Kiver Sep 2 '15 at 19:40
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    As an new user, I wonder if you've misunderstood the interface. You appear to have clicked the Tick on the answer by dlu, indicating that that answer was the correct one (worked for you). But then your comment and this answer indicate that it's not the solution. To give credit for the effort someone takes to answer, just click the up arrow. You can undo each of these actions, but not often. – andy256 Sep 2 '15 at 22:13
  • Thanks Andy, it was probably a mis-click while struggling to edit things on my primitive mobile. Rectified now though I see the resultant rep changes now mean I can't up vote things until I hit 15 again. – Kiver Sep 3 '15 at 15:58
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As previously stated, a picture or two would help answer this question accurately. Even without a picture, some information is missing. What kind of cassette is it, and how many front chain rings do you have? Because if you have 3 cogs on the front, (depending how many gears you have on your cassette, for this answer I'll assume you have at least 9), then running any of your large cogs on the rear cassette with your large chainring on the front (cross chaining) puts considerable stress on your drive train and all of its components.

Without all of the information, I can only speculate what I believe your problem is. Listed is a picture explaining it. enter image description here

If this is the case, and especially if you ride in this manner often, your rear mech might be permanently damaged. I would recommend taking it to your LBS to see if they can help you out.

  • You're right that the problem being described happens while cross chaining, but it's also a new problem – it didn't used to happen. So the puzzle for us is why? What's changed or failed that could be causing the problem. To me, it sounds like the chain has mysteriously become "too short." Any ideas how that could have happened? – dlu Aug 31 '15 at 6:25
  • I could only really think that this problem didn't occur over night. If the OP had been riding like this intermittently over a short period of time, there would probably not be any real damage done. But if they employed that gear selection continuously over, say, six months, the problem could have just gotten worse and worse, without the OP even noticing it, until now. – Weirix Aug 31 '15 at 6:30
  • However, to entertain a different possibility, I would also think that instead of the chain "shortening", maybe the OP has the gear cables tightened extremely tight, there fore making the larger sprockets pretty much not operable. – Weirix Aug 31 '15 at 6:33
  • Hard to say without a photo, or more information. We can only speculate. – Weirix Aug 31 '15 at 6:33
  • Thanks, it's an 8 speed Shimano Claris, double chain ring setup with an 11-30 cassette. I;m aware of cross chaining and would never normally ride big ring - biggest cog but I do run down to the 50/23 combination (big ring to 3rd biggest sprocket). I'd just cleaned the bike/drive train and re-lubricated the chain (a job I do regularly) and then noticed this gear or indeed the 50/26 or 50/30 combination (ones I would never use on the road) wouldn't engage the jockey wheel when on the stand. – Kiver Aug 31 '15 at 9:29

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