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I can't find replacement pulley wheels for my derailer that are explicitly made for it. Should I be safe replacing them with a set with the same number of teeth (i.e., the same diameter) and targeted at the same "speed" chain? I figure the "speed" of the chain would be a good proxy for the axle width of the pulley; is this actually the case?

If not, is this difference just dependent on the company that produces the pulley wheel? Should I be safe replacing a Shimano pulley wheel on a ~3 year old Shimano derailer with a current Shimano pulley wheel?

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    Can you tell us what happened to the old jockey wheels? If this bike has munched one in three years, something may be wrong and the next one will fare no better. – Criggie Oct 25 '15 at 3:40
  • It would also not hurt to state what derailleur you're using. – Batman Oct 25 '15 at 15:17
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    I've actually had to replace my whole drivetrain. It was three years, with about 50,000 miles, quite a bit of which was in snow or rain. The derailer is a Shimano Tourney TX55 (part RD8154), which doesn't show up on Shimano's official consumer website. It has two 13 tooth jockey wheels, which don't seem to be very common in adapter sets. I wanted to make my question as generally applicable as possible, so I didn't mention my specific derailer. – T.C. Proctor Oct 26 '15 at 1:18
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You'll probably be fine if you buy the wheel from the new version of what you have now. Probably. Shimano especially have a reputation for tweaking things just enough that last years parts don't fit.

The real issue is the axle diameter at the centre of the jockey wheel. If that matches the rest is likely to be fine. Unfortunately there's no real way to work this out from online photos or specs, since it's not one of the things that's listed (it only matters to people in your position, no-one else)

If you can find someone with the new derailleur who will let you take it apart to compare jockey wheels that would be ideal. A bike shop is likely to have one in stock that they can do this with, but the labour cost will probably be more than the price difference between the parts and the whole derailleur.

This is another case where if you have the second hand parts handy, try them and see what happens. If you can, it's probably better to scrounge a cheap/free second hand derailleur rather than buying new parts. IME a lot more people break rear derailleurs than wear then out, so it should be relatively easy to find someone who has a broken one with working jockey wheels. I'd try your local bike recycling group if you have one, or a tip shop. Basically, anywhere with a big pile of donated bikes that you can pick through.

If that fails or isn't an option, I'd look very carefully at the cost of replacement jockey wheels that might work compared to the cost of a new derailleur that definitely will work.

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  • Agreed - I've looked at replacement jockey wheels, and two would have cost me more than a whole derailereuruer. If I'd gone for $2 chinese ones they might have fitted, but longterm reliability is questionable. Remember what happens if a jockey wheel collapses? Your chain will likely snag and stop or worst case snap. – Criggie Oct 25 '15 at 3:39
  • Do you have a source for different axle diameters? Aftermarket ones from Tacx and BBB come with a bunch of different adapter shims of different thicknesses but all have the same axle diameter. – ojs Oct 25 '15 at 12:46
  • @ojs not an online one, just a box of old derailleurs including a selection of jockey axle bolts in different sizes. – Móż Oct 25 '15 at 20:09
  • @Mσᶎ interesting, how old and which brands? – ojs Oct 25 '15 at 20:23
  • Mostly Shimano, a couple of Campag and some BSO brands. Mostly they have a 6mm or 8mm shaft... mostly. I don't have many recent ones, so that advice might not apply to stuff from the last 5 years. – Móż Oct 25 '15 at 20:47
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For Shimano derailers, you may be able to find interchangeability information online on Shimano's website, but it's not easy to find. http://si.shimano.com/ has "exploded views" of their products which have a handy "interchangeability chart". These seem to be really badly edited though, as I have found quite a few where the interchangeability is mentioned for one derailer but not vice-versa. I think the best way to get a more exhaustive interchangeability list is to just google the "SHIMANO CODE NO." for the part you're looking for, which can be found on the chart in the exploded view of your product. This comes up with a nice list of all the other exploded view PDFs on Shimano's website that include the same part. You can than order the part that goes with any of the products in that list.

This helped me find the exact same pulley wheel I was looking for, however there may be other sources for parts that will work just as well, though they may not be an exact match.

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The jockey wheels are fairly standard, with few different tooth counts and small differences in thickness. If you are in doubt about the exact thickness, there are aftermarket pulleys that come with sets of adapter shims for different thicknesses. Get one that has matching tooth count and chain width, and use a vernier caliper to find the adapter that has closest width.

Edit: SRAM has very obviously different bearing and needs different replacements.

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