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I have an SRAM x7 rear derailleur only been using it a few months (through the rain) and the jockey wheels seem in a bad way. There's a lot of side to side play in them and the teeth look sharp when i think they should be squared off at the top, I think this is causing issues in a couple of gears which won't setup correctly. The rest of the drivetrains is brand new and seems to be working fairly well.

Given how expensive jockey wheels are, Is it generally worth replacing the jockey wheels in a derailleur at this point, or is it better to get a new derailleur. Seems a waste as I think its been on the bike for 4 months max.

Edit from comments:
Having examined this further. It looks like the reason its not quite shifting correctly is that the derailleur is slightly bent. The play in the jockey wheels is not excessive, but it seems to want to run at a slight angle away from the cassette

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Jockey wheels often tend to be fairly loose on their bearings, so it's hard to tell if your description suggests a problem or not. But a set of replacement wheels is $15-25 (vs about 4x that for the derailer), so it seems to me that if you do have a problem replacing the wheels is worth a shot. – Daniel R Hicks Mar 25 '14 at 23:43
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What @DanielRHicks said. Plus derailleurs are designed to have replacement jockey wheels. A few months is a short time, I'd expect a few years, but if they're done they're done. – andy256 Mar 26 '14 at 0:57
    
not sure it is an efficent use of money to replace jockey wheels versus full RD. – Batman Mar 26 '14 at 9:31
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Go into your local bike shop and see if they have a bin of broken rear derailleurs that they use for parts (mine does). Ask them if you can grab some jockey wheels off of a busted derailleur and throw them a few bucks. – Booker Mar 26 '14 at 15:32
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Having examined this further. It looks like the reason its not quite shifting correctly is that the derailleur is slightly bent. The play in the jockey wheels is not excessive, but it seems to want to run at a slight angle away from the cassette :/. – grrrrrrrrrrrrr Mar 30 '14 at 20:15

the derailleur is slightly bent.

It's more likely that the derailleur hanger is bent. Those are often replaceable because they're a (deliberately) small and somewhat fragile part that's designed to be cheap and easy to replace.

The first step is to see if you can straighten it. Any bike shop will have the tool for this, and it's something you can't do without the tool as the adjustment has to be quite precise. This answer has more details.

It's very unlikely that you've bent the derailleur. Unfortunately an impact powerful enough to bend a derailleur is generally going to also bend the hanger. So the advice is the same - take it to a shop or buy the above tool. Once the hanger is straight you can try to bend the derailleur back if that is also bent.

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