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I've just replaced the rear derailleur and cassette on my bike. I have Shimano Tiagra 9 speed shifters. The cassette is now a 9 speed 11-32 and the derailleur a Sora RD-R3000-GS.

I've set the limits on the derailleur, but I can't get the indexing right. Either, it shifts perfectly going up but won't then drop from the 32 to the 28 ring. Or, it shifts perfectly going down, but won't then rise from the 11 to the 14 ring. I've made as small an adjustment as possible, and yet there doesn't seem to be a happy middle ground.

I've also cleaned the cable / applied bike oil and the mounting point is not bent (following the advice in Why does my rear derailleur's indexing work for either the high or the low gears, but not both?)

What am I missing?

Thanks!

  • When you say shifting 'up' do you mean from small to large sprockets (up in terms of sprocket size) or from large to small sprockets (up in terms of gear ratios)? – Argenti Apparatus Aug 29 '18 at 16:48
  • Ah darn, I was going to suggest checking the derailleur hanger alignment but you already did that. – Gabriel C. Aug 29 '18 at 17:20
  • @ArgentiApparatus ah sorry, I meant up = going to a larger ring, down = going to a smaller ring... which is totally confusing :D – James Crowley Aug 29 '18 at 18:39
  • I tend to go for the cable in the first instance. Once I went though hanger alignment, new chain and cassette, new derailleur and finally tracked to a 2 month old cable - the shop (that I no longer visit) that replaced it had squished the outer under the bottle holder. – mattnz Aug 30 '18 at 2:58
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You mentioned replacing the RD and cassette but not the chain. Unless somehow the chain is nearly new already, you should replace it along with the new cassette. Unless it's very worn, it's not likely that's what's causing this though.

This is almost always a problem with either the hanger alignment or the cable.

Cleaning and lubricating the cable does not eliminate it as a potential factor. If the housings are too short, if they're contaminated with something you couldn't clean out, or if the cable has any kinks within them, they could be causing your issue. Having too short of a rear loop in particular is a common problem.

Hanger alignemt doesn't have to be obviously bent to still be out enough to cause problems, especially if you're not used to looking at it. For better or for worse, getting it aligned with a proper tool is pretty much required to eliminate it as a factor.

  • The chain was replaced too. I'll see if I can get the hanger alignment checked, thanks. (gear shifting was fine before I switched these bits out, though) How do I know if the rear loop is too short? It hasn't changed, but the RD is obviously longer now so not sure how much that impacts things. – James Crowley Aug 29 '18 at 18:41
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    A good rule of thumb is that at the spot where the housing enters the derailer, it should be running in a straight line for at minimum about 1/2" or 12mm. A lot of bikes have them too short. – Nathan Knutson Aug 29 '18 at 23:02
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I completely agree with Nathan. Even a slight deviation in the hanger or if the derailleur is slightly bent (even around 1mm) can cause the problems that you are having. I had that problem a few months ago, when even though everything was properly indexed, bike wouldn't shift properly into one of the bigger gears. After inspecting it properly and taking a few pictures, I noticed that the cage of the derailleur was slightly bent. I replaced the rear mech and everything was good again.

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