Cogs are meant to rotate forward, not move left and right.

June 15, 2011 6:43 PM

I had to remove the cassette on my rear wheel to replace a broken spoke. There is now a small amount of movement between the cogs. Is this a problem?

Naturally, the spoke I broke was on the drive side. I'd bought the bike second hand, and had never removed the cassette before. It's an Ultegra hub, and (I believe) an Ultegra (9sp) cassette.

Before I removed it, I don't recall the cogs moving at all - they were held quite snugly between the lock piece and the inner of the hub. Now there is roughly 1mm of movement. I'm quite sure I didn't leave a spacer out, and the lock piece is firmly tightened. I did clean a bit of built up grime off the cogs before I put them back on, so I'm not sure if it was that grime keeping things firm.

In a nutshell, my question is whether a very small amount of "rattle" is acceptable on a correctly mounted cassette. It seems to cause no problem when riding, shifting gears, etc.

posted by chmmr to Sports, Hobbies, & Recreation (13 answers total)

There shouldn't be that much play in the cassette assembly. Is there movement between the cogs, i.e. can you slide the smallest cog individually back and forth like an abacus? The lockring should be firmly seated against that cog, that cog against the rest of the cassette, and the rest of the cassette against the back of the freehub body.
posted by lantius at 6:55 PM on June 15, 2011

Response by poster: The smallest cog doesn't move. The lock piece is firm against that. Everything inward from that does move a little. When I was putting it back on, the smallest cog didn't seem to slide onto the freehub any further than just the outer few mm. I assumed at the time that was a feature, not a bug. Perhaps not so?
posted by chmmr at 7:05 PM on June 15, 2011

Are you sure you put the smallest cog on the right way? If you were to have flipped it over, it would slide further down the freehub and give you that play. The side next to the lockring should be grooved for extra traction and the side by the next larger cog should have the part that spaces it out.
posted by advicepig at 7:37 PM on June 15, 2011

Response by poster: The part of the cog that spaces it out is facing inwards, i.e. is between the smallest cog and the next-biggest cog, so yes, I'm sure that's correct. Thanks though.
posted by chmmr at 7:49 PM on June 15, 2011

The smallest cog is keyed just like all the other cogs. There should be a small arrow on the outside of the smallest cog, this arrow will line up the widest spline on the cassette. Once it's all lined up correctly there should be no play in the system.

I would also wipe any dirt/grime off each cog and spacer to make sure they all seat against each other correctly.
posted by Confess, Fletch at 7:59 PM on June 15, 2011

Here's a nice pic of the arrow and widest spline that I mentioned.
posted by Confess, Fletch at 8:04 PM on June 15, 2011

I would not accept that kind of rattling, no. You seem confident that you didn't leave a spacer out -- that would have been my question.
posted by chinston at 8:14 PM on June 15, 2011

It's also possible that you've got an older, non-Hyperglide-C cassette body and didn't notice the lateral play before (perhaps it was gummed up?). See Sheldon Brown's explanation with handy graphic. You'd end up with exactly a millimeter of play installing an 11t-based cassette.
posted by lantius at 8:19 PM on June 15, 2011 [1 favorite]

I have the same hub and cassette. (Mine goes down to 11t at the smallest; some models are 12 or 13.) There's no rattle; everything is tight as a drum. Check the shimano tech docs for the CS-6500: parts list and installation instructions. I would tear it down and reinstall.

My guess: either you have an incompatible freehub body and just noticed it, or you left out a spacer.
posted by supercres at 9:16 PM on June 15, 2011

This is the second time in the last few days I've wanted to recommend taking the Park Tools School program here on the green - I LOVE folks who tinker with bikes!

Don't be afraid to take your bike in to a good technician this time around if you can't figure out the issue, and do take that class if you can find one in your area.
posted by jbenben at 10:29 PM on June 15, 2011

Response by poster: Okay. Tonight I removed the cassette again and put it back together with an extra spacer. After that I couldn't get the 9th cog onto the hub. I removed the same spacer and put it back together again. Everything tightened up nice and snug, no play anymore.

So, shrug. My best guess is that I originally somehow put the last cog on incorrectly, though I don't see how that's possible. In any case, all good now. Thanks very much all for the input.
posted by chmmr at 5:45 AM on June 16, 2011

Last time I tore into my drivetrain (to convert from 7 speed (with spacer) to 9, I was *certain* I put it back together properly and yet ended up with a nasty bit of play (more than yours) that I had to dis/reassemble to fix (only noticed days after the fact). Don't really know why it ended up messed up, but I guess it's something that's easy to mess up at the end of the job. Either an incorrect spacer or lockring not tightened enough, I guess. Maybe the spacer shifts during tightening sometimes?
posted by RikiTikiTavi at 8:27 AM on June 16, 2011

Response by poster: I swear sometimes the bike gods do this sort of thing just to mess with our heads. :)
posted by chmmr at 4:44 PM on June 16, 2011