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I recently bought a new wheel for my racing bike. The first few rides were in rainy weather so I took the cassette off to clean it. When I put it back on I noticed that there was a gap of several millimetres between the outer sprocket and the lock ring. As a result the two outer sprockets (the ones separate from the rest of the cassette) wobble quite noticeably when I rotate the wheel. The cassette was fitted by the LBS where I bought the wheel. It is 8 speed (Shimano) and has 12 teeth on the smallest sprocket and 25/26 on the largest.

I have another 8 speed cassette on my bybrid bike. That had 32 teeth on the large sprocket and fitted just fine when I put it onto the racing bike. Likewise both cassettes fit ok on the wheel of the hybrid bike.

Having looked at other answers on this site, it seems like the most likely explanation is that I mislaid a spacer when I removed the cassette. Does that seem right, or is there another possible explanation which I have missed.

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    Does it have a spacer? You don't typically need to remove a cassette to clean it. – paparazzo Aug 9 '17 at 0:52
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    if you misplaced the spacer, then the 32 tooth cassette from your hybrid should also have the same problem with being loose – Kibbee Aug 9 '17 at 1:03
  • Thank you. Paparazzi - not sure if it was meant to have a spacer. I don't remember seeing one, but the fact that the outer sprockets are loose maybe suggests there was one. – Chris Aug 9 '17 at 11:08
  • Kibbee - I will triple-check tonight, but the hybrid cassette fits snugly onto the racing bike. This seems quite strange as it means the two cassettes have the same number of sprockets (and are the same make I.e. Shimano) but are a different width. – Chris Aug 9 '17 at 11:11
  • Paparazzi - I would not personally recommend ever leaving the cassette on the wheel to clean if it it's a deep clean using anything other than water and a brush. Degreasers will get into the free-hub body and hub bearings and break down the grease there. I get a bike about every other week that needs the hub cleaning and re-greasing almost exclusively because of this problem. – yollooool Sep 1 '17 at 16:02
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Seems like I'm a Necromancer again...

Most likely a spacer. No, I take that back; Almost certainly a spacer. With the Hybrid cassette fitting correctly, it's quite often that they are slightly thicker, even by a couple of millimeters. An easy way to check is to check the limiter screws on the deraileur if you haven't adjusted them. If there's too far away from the wheel for where the jockey wheels line up, it's probably missing a spacer. If not, it needs a thicker spacer or more, assuming the gears were properly set up before you took it to pieces.

Also, good call, taking the cassette off to clean it. Too many times, people leave it on their wheel using a degreaser to clean it, and it breaks down the grease inside the hub and freehub body! Annoying because I usually get asked to replace them when it happens, then I lecture them about all the problems from doing so..... Boring!

  • Good answer - you can add info about the two different spacer locations - could be a shim between first and second or second and third smallest cog (if so its sub 1mm difference and will affect chain spacing in the smaller cog, OR its a spacer that goes inboard of the whole cassette and could be 2-4mm difference. Use Edit to enlarge your answer. – Criggie Sep 1 '17 at 21:13

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