I recently purchased and am now installing a 9 speed Deore XT cassette sprocket (CS-M770) on a Specialized Stumpjumper FSR XC. It's replacing a CS-HG50-9, and is mounted on a Shimano rear hub (FH-M525). The Shimano shop instructions and exploded view diagram a "lockring spacer" and on the exploded view the part number for this spacer has an asterisk by it. However, there's no note or other asterick on the page to explain this. Anyone know if the lockring spacer comes included with cassette (brand new out of the box from Chainreaction Cycles) ? Also, I've never seen a spacer used in this position prior, but this is by far the fanciest and lightest cassette I've dealt with. Installation went normally and I only caught this business about the lockring spacer because I simply wanted to add the SI and EV download files to my laptop's collection of bike part files.
Thanks in advance.

  • Upon further review: I see now that the "lockring spacer" Shimano refers to (and does include with the new cassette) is a mere foil-thin washer. To label it a spacer--or even a washer--is quite a stretch, even given the copious ambiguity of the English language. – Jeff Jan 8 '19 at 3:11
  • At any rate, all is well, and upon sizing, cutting and connecting the new chain I'm off for a shakedown ride. Moderators, feel free to advise the proper handling of this too-hasty question or delete altogether – Jeff Jan 8 '19 at 3:16
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    You can reply and accept your own question, that's perfectly fine. – Klaster_1 Jan 8 '19 at 6:37
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    Concur - there's value in providing a complete Q&A for future searchers who may have the same question. – Criggie Jan 8 '19 at 10:35

The "lockring spacer" (so labelled on Shimano Exploded View diagrams and other technical documents) is a very thin metal washer or shim between the lockrings of higher- end cassetes such as XT, Ultegra, and the like. Normally it is held captive on the lockring, and based on Q and A from other forums (see example here: https://forum.cyclinguk.org/viewtopic.php?t=122213#p1235924) this little bugger is often installed unseen or the inexperienced-but-fully- prepped-with-technical-manuals mechanic is given lengthy pause as the search for this "spacer" commences. It is included with the appropriate cassettes in it's correct position. As mentioned, higher end cassetes utilize this washer/spacer/shim between lockring and first position, high, sprocket as a means of protecting the integrity and functionality of the serrations of the associated lockrings, which in these upper-tier models is not steel but rather aluminum-alloy. This thin little washer then, "protects small peaks of those serrations getting worn off by cassette removal and replacement." A more in-depth reasoning: "There are about 100 teeth in the serration and the screw thread is ~1mm pitch which means that each 'click' results in ~10 microns (less than half a thou') more compression. However the serrations are about 250 microns high which means that with metal spacers in the cassette, the lockring may never tighten enough unless the metal shim is fitted. Plastic spacers are more elastic which allows the lockring to tighten more easily. However with plastic spacers in the cassette they can 'relax' over time which results in a reduced clamping force and can often allow the lockring to go up about another 1/4 turn once the thing has been installed for a while (enough to cause problems with indexing accuracy in fact). Metal spacers don't relax but both metal and plastic spacers can wear thinner if the sprockets start to move around (which they will do, all the time, if the lockring doesn't provide an adequate clamping force)." So there's some light shed on the very slim shim. Look (closely) for it on your next top-end cassette.

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    Don't forget to accept the answer ;) – Klaster_1 Jan 9 '19 at 9:50
  • @Klaster_1 How do I do that? Ive scanned around and can't seem to find even a "help" link. Apologies – Jeff Jan 9 '19 at 10:26
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    @Klaster_1 please disregard that. I no sooner sent that comment when the bottom of the page appeared and the HELP link poked me in the eye. Lol. In 13 hours I can accept it. Check. Thanks for the heads up – Jeff Jan 9 '19 at 10:31

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