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  1. #1
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    Sudden chain slack at high speed

    After a great climb today, I was riding down a long hill & while coasting at high speed (maybe 65-75 km/hr), the bottom portion of my chain suddenly became slack & there was a loud noise that sounded like something rubbing. I stopped immediately & checked to see what may have caused it, but I could see nothing wrong. The same thing happened several times on the 14km downhill from the ski area. Basically every time I'd get up to high speed & coast. I was not touching the shift levers at the time. The final time it caused the chain to come off. It seems very dangerous. I can't figure it out. The bike shifts perfectly. It's a Specialized Allez with 105 rear der. Anyone have an idea of what could cause this?
    Thks

  2. #2
    rebmeM roineS JanMM's Avatar
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    What gear combination were you in when it happened and is that the same combo you found the chain to be in when you stopped to check it out?
    The final time the chain came off what? The chainring? Which one?
    RANS V3 (steel), RANS V-Rex, RANS Screamer

  3. #3
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    Check your chain for a stiff link. Work the side plates around each pin to assure that they are not binding. Bad things can happen if a stiff link fails to go through the rear derailleur.

  4. #4
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    Quote Originally Posted by joemil View Post
    After a great climb today, I was riding down a long hill & while coasting at high speed (maybe 65-75 km/hr), the bottom portion of my chain suddenly became slack & there was a loud noise that sounded like something rubbing. I stopped immediately & checked to see what may have caused it, but I could see nothing wrong. The same thing happened several times on the 14km downhill from the ski area. Basically every time I'd get up to high speed & coast. I was not touching the shift levers at the time. The final time it caused the chain to come off. It seems very dangerous. I can't figure it out. The bike shifts perfectly. It's a Specialized Allez with 105 rear der. Anyone have an idea of what could cause this?
    Thks
    Sticky freehub.

  5. #5
    Senior Member oldbobcat's Avatar
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    Quote Originally Posted by Drew Eckhardt View Post
    Sticky freehub.
    Or a loose spoke protector.

  6. #6
    Insane Bicycle Mechanic Jeff Wills's Avatar
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    Quote Originally Posted by Drew Eckhardt View Post
    Sticky freehub.
    Yep. Put it on a workstand and spin up the rear wheel. Stop the cranks and see what happens.
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  7. #7
    rebmeM roineS JanMM's Avatar
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    You guys are good.
    RANS V3 (steel), RANS V-Rex, RANS Screamer

  8. #8
    Insane Bicycle Mechanic Jeff Wills's Avatar
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    Quote Originally Posted by JanMM View Post
    You guys are good.
    All the advice given here is worth exactly what we charge for it.
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  9. #9
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    Quote Originally Posted by JanMM View Post
    What gear combination were you in when it happened and is that the same combo you found the chain to be in when you stopped to check it out?
    The final time the chain came off what? The chainring? Which one?
    First time it happened: Big ring front, small ring back. Then, since I was coasting anyway, I switched to small front, middle back & it happened again. I experimented w/diff combinations, but it happened again. When the chain came off, it came off of the front big ring.

  10. #10
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    I don't have a spoke protector & I've checked the chain & all of the links seem to be ok. I put the bike on a stand & spun as quickly as I could, then coasted, holding the crank arm. I couldn't replicate the problem. If I spun the crank arm backwards a little, then let go of the arm, it seemed to spin slightly with the wheel direction then stopped. I don't know if this is normal, but it didn't seem that significant. Not sure if this helps, but when the incident occurred on the road, the noise was a pretty loud whirring sound, kind of like when I was a kid & used a clothes pin to attach hockey cards to the frame so they'd rub on the tire & make noise. Maybe that was an internal noise in the hub?? I saw no indication of any external rubbing or abrasion. Thanks for your thoughts on this.

  11. #11
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    Still sounds like a failing freehub. Unless you can spin your wheel at close to the speed you hit you likely will not be able to reproduce the problem on a stand. I have had 2 failures of freehubs. One was instant with no warning and the other did just as yours did and would start failing at high speeds. You can still ride that bike, just not at high speeds until you get that hub replaced (unless you want the pedals to suddenly start spinning to match your wheels).

  12. #12
    Quirky Grifter LesterOfPuppets's Avatar
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    Freehub body replacement is usually cheaper and easier than entire hub replacement.

    When a freehub body gets gunky like that it usually just needs to be cleaned out and re-lubed. Often even the introduction of some fresh light lube (I like Tri-flo for this) will be enough to free up the gunk and get it back to normal.
    1980ish Free Spirit Sunbird fixed * 1996 Mongoose IBOC Zero-G * 1997 KHS Comp * 1990-ish Scapin * Lemond Buenos Aires Triple

  13. #13
    Insane Bicycle Mechanic Jeff Wills's Avatar
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    Quote Originally Posted by harshbarj View Post
    Still sounds like a failing freehub. Unless you can spin your wheel at close to the speed you hit you likely will not be able to reproduce the problem on a stand. I have had 2 failures of freehubs. One was instant with no warning and the other did just as yours did and would start failing at high speeds. You can still ride that bike, just not at high speeds until you get that hub replaced (unless you want the pedals to suddenly start spinning to match your wheels).
    +1. I had a Shimano freehub fail in the middle of a tour. While coasting, it would catch, cause the chain to jump forward, then work normally for a few miles. It got worse as the day wore on. Eventually I just stayed in a higher-than-normal gear and limped it to a mechanic. When we pulled the hub apart, the freehub body was completely broken and it spilled many small bearings all over Canada. The mechanic loaned me a wheel so I could finish the day and had the wheel repaired that night.
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  14. #14
    Insane Bicycle Mechanic Jeff Wills's Avatar
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    BTW, Joe: are you in this Vancouver or that Vancouver?
    Jeff Wills

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  15. #15
    Roadkill byte_speed's Avatar
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    Quote Originally Posted by Drew Eckhardt View Post
    Sticky freehub.
    I had a wheel bearing fail (due to water ingression) that allowed the freehub to rub the wheel a bit, which made the chain go slack. The problem was somewhat intermittent and jerky, but did not depend on the gear combination.

  16. #16
    Senior Member Ira B's Avatar
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    Agree about the freehub. I would no longer trust it.
    Yep, THAT Ira

  17. #17
    bike whisperer Kimmo's Avatar
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    Is it a Shimano hub?

    65-75 clicks really is quite fast; it occurs to me that some designs of freehub may be more vulnerable to this problem than others, because of centrifugal force on the pawls causing higher friction against the ratchet teeth...

    Anyway, you should be able to make the chain go slack like this on the repair stand, so you can mess around tuning your freehub (Shimano cassette bodies are rebuildable) until the problem's fixed.
    Last edited by Kimmo; 07-04-11 at 02:56 AM.

  18. #18
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    These descriptions are sounding very similar to my problem. Still can't replicate it on the workstand, but maybe I'm not able to spin fast enough by hand for a long enough period (It would do it each time I went really fast, but usually after maybe 5-15 sec of maintaining the speed). Taking the wheel into the shop today. Hopefully they don't give me blank looks & tell me it's perfectly fine.
    Kimmo - It's a Shimano free hub. ps. LOL - I know 65-75 clicks is "really quite fast." Not my normal thing at all, but I was hauling down Cypress Bowl road (I think around 14k down hill from ski hill area), doing some training for the Granfondo Whistler ride in September which has a lot of hills, both up & down. Almost impossible not to go fast on the down hill part.
    Jeff - I'm in the Vancouver w/the Olympics & the Stanley Cup riot (depends how you want to describe it).
    Thks for the help everyone. Will report back results of the forensic hub analysis.

  19. #19
    coprolite fietsbob's Avatar
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    Take the freehub off, flush it out , re lubricate in a lighter, weight oil,
    say Phil Tenacious ,
    then grease the axle bearings, as you put it back together.

  20. #20
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    Just dropped the wheel at the bike shop. Mechanic said it's not uncommon & he'll inspect/lubricate ($10) or possible replacement parts if damage (likely $35 or so). I told him re: louder than avg clicking when coasting (as compared to my buddys' rides) & he said that's caused by lack of lube as well. He said I should bring it in every 6+ mo's to get this maint done. Otherwise, it looks like I'd need a couple of extra tools to remove cogs to get at free hub for lube. Kind of like the idea of acquiring some tools to do these maint type things myself though, so maybe I'll call my first $10 as a training fee & get set up for this.

  21. #21
    coprolite fietsbob's Avatar
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    a 'Freehub Buddy' will push lube thru the free-hubs pawls and bearings..in site , a good tool to own.
    still have to take the axle out , but thats really easy if you have some cone wrenches..

  22. #22
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    Freehub cleaned, lubricated for $10. 25k commute this morning & it was almost silent! Mechanic said it was basically bone dry in there, but no damage. I know now that a loud clicking from the freehub is not normal & indicates that lube is needed. Thanks for all the feedback.

  23. #23
    bike whisperer Kimmo's Avatar
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    Shimano freehubs are easy to overhaul yourself; you can make a tool to unscrew the cup out of a bit of plate. You crack the cup, then remove the cassette body from the hub before unscrewing it.

    I guess you need fairly steady hands to line the balls up in the races, but it's not hard. Often you can remove a shim or two, which is nice.
    Last edited by Kimmo; 07-07-11 at 09:35 AM.

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