Noisy vibration, but stops when..

plymouthsteve
plymouthsteve Posts: 136
edited January 2014 in Workshop
When I go down a long hill without pedaling, I get a vibration which is quite noisy. It seems to be coming from the bottom of the frame around the BB area.
Strange thing is that if I pedal even slightly and without any force, the noise / vibration stops for a few seconds before coming back again.
Bike is a Specialized Roubaix, so carbon, with 105 group.
Any ideas?
Thanks

Comments

  • taff..
    taff.. Posts: 81
    have you checked the rear wheel bearings?
  • plymouthsteve
    plymouthsteve Posts: 136
    No, I haven't.
    I've got Mavic Ksyrium Elite S which are about 18 months old. I suppose Ive 4-5000 miles on them. Wouldn't they feel loose if they were worn though?
  • bobones
    bobones Posts: 1,215
    Sounds like the freehub could need some lubrication. My old Aksiums started making a weird noise/vibration when freewheeling, which was quite alarming at the time. Easy to fix by removing the freehub body and lubing the rubber contact bearing with mineral oil.
  • littledove44
    littledove44 Posts: 871
    I have the same bike.

    I think it is the chain slapping the stay. Only happens downhill, smallest cog, biggest ring, not pedalling.
  • Secteur
    Secteur Posts: 1,971
    littledove44 wrote:
    Only happens downhill, smallest cog, biggest ring, not pedalling.

    Are you a mountain biker?

    Seriously though, it's your freehub
  • lesfirth
    lesfirth Posts: 1,382
    What does nothing when you are pedalling and only works when you don't?

    Only one answer. Freehub
  • bobones
    bobones Posts: 1,215
    This video may be useful http://vimeo.com/51942337 although exact details for removing the freehub body may be different on your wheels.

    See docs at http://www.tech-mavic.com/ (login: mavic-com pass: dealer)
  • littledove44
    littledove44 Posts: 871
    Well he may have a free hub problem, but that is not the issue on my identical bike. It is definitely the chain hitting the stay.

    The reason I know this is that I got someone else to ride my bike. I rode his alongside and watched it doing it. I even reached over with by pump, lifted the chain and dropped the noise.

    It's a giveaway if it only happens on non-smooth roads as is my case.
  • keef66
    keef66 Posts: 13,123
    "The reason I know this is that I got someone else to ride my bike. I rode his alongside and watched it doing it. I even reached over with my pump, lifted the chain and dropped the noise".

    Bloody hell, that's good group riding skill! Did you not consider the possibility of one of you wobbling and putting the pump into the spokes?? :shock:
  • dee4life2005
    dee4life2005 Posts: 773
    If the noise is caused by the chain hitting the stay, then there could be a tell-tale black stripe across the chainstay. If this is the case I've found this is usually because the rear-derailleur is in need of a good clean (best done with it off the bike) as the muck is stopping the return spring taking up the chain slack.
    http://app.strava.com/athletes/307297
  • pashda
    pashda Posts: 99
    my mate had the same thing with his Mavics on the RideLondon. we stopped for mechanical help and the wonderful expert told us it was a common thing on Mavics cos they are French rubbish and we should have bought handbuilt wheels. He stripped the hub re-greased it and it did the trick. Not sure it is only a Mavic issue really, he was just proper old school and these modern wheels are no match for his proper hoops etc etc. We didn't argue just smiled and said thanks

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