{"id":17924,"date":"2014-06-08T16:55:26","date_gmt":"2014-06-08T20:55:26","guid":{"rendered":"https:\/\/nuxx.net\/blog\/?p=17924"},"modified":"2014-06-08T16:56:08","modified_gmt":"2014-06-08T20:56:08","slug":"shimano-xt-freehub-y3cz98040-failure-analysis","status":"publish","type":"post","link":"https:\/\/nuxx.net\/blog\/2014\/06\/08\/shimano-xt-freehub-y3cz98040-failure-analysis\/","title":{"rendered":"Shimano XT Freehub (Y3CZ98040) Failure Analysis"},"content":{"rendered":"

\"\"<\/a><\/p>\n

The failure of the Shimano XT freehub (Y3CZ98040) on the El Mariachi Ti was frustrating<\/a>, so I wanted to understand what really went wrong. As far as I can tell, the root cause\u2020 is a freehub shell that cracked, allowing at least one bearing to become displaced and work its way into the ratchet mechanism. This caused the symptom of the freehub being extremely hard to turn, moving with very solid, thunking sound when forced.<\/p>\n

No preventative maintenance would have caught this, and without inspecting the freehub regularly for hairline cracks (a really difficult task) I wouldn’t have known this problem was starting.<\/p>\n

The evidence for this is as follows, with photographs:<\/p>\n

    \n
  1. The freehub shell was cracked, which I found when trying to disassemble it. I ended up breaking it in two pieces to get it apart, and there are two visible fractures where it broke: a bright, clean one from breaking it apart today, and an oxidized one from the original failure. (Photos: Oxidized break<\/a>, new\/clean break<\/a>.)<\/li>\n
  2. All of the pawls are intact and with sharp edges.\u00a0(Photo<\/a>)<\/li>\n
  3. There is a worn groove next to the bearing race, but just beyond a lip, which leads back to a\u00a0recess along the center of the pawl mechanism. I suspect this is where one of the small bearings which came loose worked its way towards the ratchet.\u00a0(Photo<\/a>)<\/li>\n
  4. There are rounded, ball bearing sized witness marks in the fixed tooth part of the ratchet mechanism in a location which correlates to where the ball bearing is thought to have settled after settling in the recess.\u00a0(Photo<\/a>) There are other, smaller witness marks which make me suspect that even more bearings worked their way into the pawls once the failure really took hold. This could explain how I noticed the failure briefly a couple of times before the hub completely locked.<\/li>\n<\/ol>\n

    This aligns with problems\u00a0reported here on MTBR<\/a>, and this post from that thread<\/a>\u00a0states that Shimano has changed the design and heat treating to address this.<\/p>\n

    In order to disassemble the freehub I first tried fashioning a tool (flat piece of steel about 29mm wide, 4mm thick, and at least 20mm long: photo<\/a>) to unscrew it. This didn’t work because I did not have a tool for holding the Shimano splined end, but it spread open the\u00a0crack enough for me to see what the problem was. I then clamped it in a vice, used\u00a0a screwdriver to break it open, and then used a wrench and a screwdriver to pry the\u00a0pawl-holding part of the ratchet mechanism out.<\/p>\n

    This worked pretty well, and after a bit of degreasing I had a clean part. The only downside is the 2.93mm ball bearings used in the hub (photo<\/a>), which shot\/flew\/fell all over my workbench and feet when the hub gave way. It’s one of these bearings that worked its way into the ratchet and caused the failure.<\/p>\n

    \u2020 This root cause is only from my perspective. The proper root cause<\/a> is much deeper than this, perhaps a human or design error that\u00a0resulted in improper heat treating or sizing of the freehub body, but that’s further than I can reasonably go; something that\u00a0Shimano would be looking into. Or, as evidenced by the redesign, already did.<\/p>\n","protected":false},"excerpt":{"rendered":"

    The failure of the Shimano XT freehub (Y3CZ98040) on the El Mariachi Ti was frustrating, so I wanted to understand what really went wrong. As…<\/p>\n

    Continue readingShimano XT Freehub (Y3CZ98040) Failure Analysis<\/span><\/a><\/div>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[10],"tags":[],"class_list":["post-17924","post","type-post","status-publish","format-standard","hentry","category-cycling","entry"],"amp_enabled":true,"_links":{"self":[{"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/posts\/17924","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/comments?post=17924"}],"version-history":[{"count":2,"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/posts\/17924\/revisions"}],"predecessor-version":[{"id":17926,"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/posts\/17924\/revisions\/17926"}],"wp:attachment":[{"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/media?parent=17924"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/categories?post=17924"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/tags?post=17924"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}