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I'm trying to repair my bike for the first time, so i'm learning.

It's a shimano deore set for a flat handle road bike.

It won't stay in gear --- it keeps shifting while i ride, especially in the middle gears of the back cassette (first and last gear seem to stick better). It's especially an issue when i start pedaling backwards... the chain is completely undecided between 2 gears at almost all times.

I've already tried adjusting it the regular way, and it's not the issue.

At closer inspection, i'm noticing that the pulley wheel labeled "Shimano - Centeron G-Pulley" doesn't spin perfectly straight. It sort of "wobbles" while it spins, and so... my chain sort of wobbles to the left and right as it spins around it. This makes the chain keep jumping gears. I understand that it is supposed to be able to "slide" to the left and right a little bit (the "centeron" tech, lol)... but in this case... it wobbles ever so slightly.. .and i'm not sure if that is okay, and if it means i need a new pulley.

I took the part out and cleaned it. I put it back in, and it still wobbles. Is my diagnosis good? Should i order a new pulley set?

  • Is it wobbly like an out of true wheel, i.e. actively pushing the chain left and right while it rotates or just moving passively, i.e. it gets pushed to the side if the chain comes in slightly from the side? The latter should be normal, the former not. – Benedikt Bauer Jun 12 '15 at 9:50
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    It was like the former, and turns out it wasn't the problem. I guess the wobbly is normal. I had to disconnect the cable and start over... i believe the cable was too lose previously. – Ralph N Jun 15 '15 at 14:07
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The wobblings fine - its likely you need to replace the cable as it stretches over time. You might also have to reindex the gears - but try replacing the cable first

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    A stretched cable doesn't necessarily need replacing. It shouldn't stop the gears being adjusted. It's more likely the cable is sticking in the outer somewhere so it could need replacing or just cleaning out. – Holloway Jun 12 '15 at 10:01
  • Turns out it wasn't the wobble... you were right. – Ralph N Jun 14 '15 at 2:12
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    Apparently the wobble is totally normal. I disconnected the derailleur cable and started from scratch, and everything works fine now – Ralph N Jun 14 '15 at 2:13
  • Most modern derailleurs have a wobble deliberately designed into the pulley closest to the cluster. If you do take the cage apart, it's important to remember which one is the top one. – Fred the Magic Wonder Dog May 9 '19 at 16:31

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