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  1. #1
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    XT 788 rearhub toast after 500km..

    the 142x12mm hub that is.
    Approx 500km on it and now sometimes loud grinding noises when pedalling and at other times when freewheeling.. Tdy it also seized completely turning bike into a 2x9 Fixie.Managed to "break" it loose again and made it home.
    Also have visibly play at the cassette , but no play in axel , so def. a freehub body problem.
    I wonder if the internals are too small in order to make room for the 12mm axel.
    Anybody else have similar prob. with this or the XTR 142x12 hub ?
    Cheers Caspar

  2. #2
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    Problem identified !!

    Took the cassette off :

    More pics here
    https://picasaweb.google.com/casparbc/788Freilauf

    Standard Shimano HG61 12-36 cassette , correctly mounted and tourqued.
    Is this the ISIS of rearfreehubs ?? or was I just unlucky ??

    Ahh the joys of mailorder( from another country) : mailordershop wants me to return whole hub w/o rim.
    Guess Itll be cheaper and faster to order a new complete hub and replace freehubbody myself

  3. #3
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    Yeah, it looks like you may have broken it. Have you contacted Shimano for a freehub body? You're gonna need a biiiig allen wrench to get that thing off.

  4. #4
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    what size granny ring are you running? if its a 22t, then your torque load on the hub might be too high in your lowest gear. get a new freehub body (shimano part number Y3TH98050) and switch your granny ring to a 24t. that should stop that from happening again.

  5. #5
    the catalan connection
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    Could that be caused by an under-tightened locknut? I mean, somehow letting something (likely a bearing cone) spin free until overloading the bearings to the point they blow the hub shell? I know this can snap an axle, but maybe they have changed something now and they just blow this way when a locknut gets free...
    "Blessed is the man who, having nothing to say, abstains from giving us wordly evidence of the fact." George Elliot

  6. #6
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    A repeating pattern for Shimano

    This doesn't surprise me. I have destroyed 6 consecutive freehubs in my MT75 shimano wheels. This is a common freehub assembly to the M770/M775 series of hubs, XT wheel WH-M775/776/778, etc. Sounds like they haven't improved it for the M78x series.

    Ever since Shimano went to the oversized aluminum axles for M77x series, the freehub became under-designed & vulnerable. I spent 20 years riding the hell out of Shimano freehubs on the original 10mm steel (or Ti) axles, and NEVER had a freehub problem, EVER. But my XT freehub on the MT75 wheels has never lasted more than 80 hours of riding. Some have only lasted 20 hours.

    I'm 6'4" and 200 pounds on a 29er w/ 180mm cranks turning a 22 x 34T, so I'm on the edge of the torque examples. But I'm not a freak example. I'm riding stock Shimano products for their intended use. Shimano should be designing beyond these requirements.

    I switched to an XTR freehub (dimensionally the same, so fits, but different materials) and I now have 160 hours on the freehub without a failure.

  7. #7
    Flying in High in the Sky
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    Quote Originally Posted by InertiaMan View Post
    This doesn't surprise me. I have destroyed 6 consecutive freehubs in my MT75 shimano wheels. This is a common freehub assembly to the M770/M775 series of hubs, XT wheel WH-M775/776/778, etc. Sounds like they haven't improved it for the M78x series.

    Ever since Shimano went to the oversized aluminum axles for M77x series, the freehub became under-designed & vulnerable. I spent 20 years riding the hell out of Shimano freehubs on the original 10mm steel (or Ti) axles, and NEVER had a freehub problem, EVER. But my XT freehub on the MT75 wheels has never lasted more than 80 hours of riding. Some have only lasted 20 hours.

    I'm 6'4" and 200 pounds on a 29er w/ 180mm cranks turning a 22 x 34T, so I'm on the edge of the torque examples. But I'm not a freak example. I'm riding stock Shimano products for their intended use. Shimano should be designing beyond these requirements.

    I switched to an XTR freehub (dimensionally the same, so fits, but different materials) and I now have 160 hours on the freehub without a failure.
    Is the XTR freehub a direct bolton or were there modifications made for it to fit?

  8. #8
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    Its a direct bolt on. XTR freehubs from 97x series will fit XT hubs from 77x series.

  9. #9
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    I should add that I am commenting only on the compatibility of XT 77x and XTR 97x, but *not* about compatibility between 77x and 78x, or even 78x and 98x. I expect that the 78x and 98x are compatible, but I haven't looked. I'd further speculate that x8x and x7x are NOT compatible, but once again I haven't investigated it.

  10. #10
    Flying in High in the Sky
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    thank you!

  11. #11
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    Blew the second freehub

    Blew the second freehub tdy , what a piece of c... this 788 hub.
    Aprox same amount of riding time on the second freehub and there she blow !
    Been on Xt hubs for some 20+ yrs , cant belive Shimano could make such a lemon.
    Obviously freehub is undersized , theres some tiny steel balls in there to make room for the 12mm axel.
    No more Shimano rearhubs for me EVER !
    Luckily I got the 12x142 axelkit for my hadley rearhub last week , time for a new wheelbuild !

  12. #12
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    XT 788 rearhub toast after 500km..

    I am just getting this wheelset. Hope I don't suffer the same fate.

  13. #13
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    Quote Originally Posted by caspar View Post
    the 142x12mm hub that is.
    Approx 500km on it and now sometimes loud grinding noises when pedalling and at other times when freewheeling.. Tdy it also seized completely turning bike into a 2x9 Fixie.Managed to "break" it loose again and made it home.
    Also have visibly play at the cassette , but no play in axel , so def. a freehub body problem.
    I wonder if the internals are too small in order to make room for the 12mm axel.
    Anybody else have similar prob. with this or the XTR 142x12 hub ?
    Cheers Caspar
    Did you adjust it so that the cones weren't too tight? You can't just stick these in there. You have to adjust them so that the axle is loose when not clamped in the frame, but not loose when it is clamped in the frame. You should also use the shimano QR's with these.

  14. #14
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    Quote Originally Posted by aBicycle View Post
    You should also use the shimano QR's with these.
    No U should NOT use a Shimano QR with a Through Axel hub ! :-)

  15. #15
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    Wow.. never before seen a steel freehub body explode.
    Had a XT-785 destroy itself after 8 rides, the 14mm bolt stripped the alu hub body.
    And it too became a fixie that provided a 4-5 mile evening hike-a-bike.
    Stripped it, and shipped it back to TFB, was warrantied, and bought a set of Hadley's.
    At 210#, it's no more Shimano hubs for me..
    The best is the one you want to ride most often..

  16. #16
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    Quote Originally Posted by What&son View Post
    Could that be caused by an under-tightened locknut? I mean, somehow letting something (likely a bearing cone) spin free until overloading the bearings to the point they blow the hub shell? I know this can snap an axle, but maybe they have changed something now and they just blow this way when a locknut gets free...
    I agree it's very likely. With a new 785 I got home and noticed the wheel was loose (rocking on the drive side end cap thread) and the cone had tightened to the point there were metal flakes in the grease ...and I never noticed riding it.
    I'd assumed this stuff was plug and play but I'd at least loctite the drive side cap and cone next time.
    Last edited by gumby.; 03-14-2013 at 03:59 AM.

  17. #17
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    Quote Originally Posted by gumby. View Post
    I had this happen with a new 785, I got home and noticed the wheel was loose (rocking on the drive side end cap thread) and the cone had tightened to the point there were metal flakes in the grease ...and I never noticed riding it.
    I'd assumed this stuff was plug and play but I'd at least loctite the drive side cap and cone next time.
    I hear a lot about bad Shimano freehubs.There's a hard to find tool that allows you to get inside of SOME Shimano freehubs...read my entry #12 in this thread...it might help.
    Z
    Are Shimano hubs rebuildable?
    roccowt.
    rocnbikemeld

  18. #18
    bog
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    that is very common with these newer XT freehub bodies. They've made the material so thin and brittle that they crack fairly easily. The XTR freehub bodies are titanium and therefore not nearly as brittle. I had bad luck with the XT version and great luck with the XTR version (240lbs and riding hard on a 29er).
    SC Tallboy C : SC Nomad 3 : Giant TCX SLR : Giant Propel Adv SL

  19. #19
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    XT 12x142 freehub body cracked. About 3 months old.

    FH-M788 started to sound clunky when riding. I could wiggle the cassette with my hand. Took the cassette off. Crack in freehub body.

    Like others in this thread, I have never broken a freehub before. I am 38 yrs old - no jumping, no drops, just riding along.

    I have a Campy Chorus hub that lasted about 25,000 miles with significant neglect. That was a training wheel in my road racing days - way more power output, way more abuse. This failure at 300ish miles is sad.

    According to this the XTR freehub body (FH-M988) is compatible with the XT (FH-M788).

    Have to check with LBS for price on XTR freehub. Probably, too much. Curses. . . .

  20. #20
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    The XTR freehub definitely fits, and it is more reliable, at least in my experience. 4 XT freehubs failed on me in 30-80 hours of riding each. I have 200+ hours on an XTR one, and its still working, although it has finally begun to exhibit some of the imminent failure symptoms (noise, wiggle) but maybe its my imagination.

    My ultimate solution was to change wheels/hubs. Got about 300 hours on an Easton Haven alloy, but eventually blew up that freehub, too. The Eastons use a normal pawl design, but the "serrated" pawl track / sawtooth ring is threaded into the hub body, not machined into it. I stripped the threads of sawtooth ring / hub body interface, such that under pedal force the entire freehub arrangement would rotate forward within the wheel. Easton claimed it was a "less than 1 in 1000 failure" but who knows.

    Now I'm on DT Swiss ratchet hubs (recent 350 models). I only have about 50 hours on it so far, but I'm hoping it lasts.

    As far as I can tell, Shimano's design is still vulnerable. They may have tweaked some materials after the early failures, but they still seem to happen, if perhaps at a lower rate.

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