Weirdest hub sound

[Abrahm]

I've got a very strange sound/problem on my Mtn bike, hoping someone can help. Local shop has no idea without tearing apart my hub as a guess. Other threads have been useless.

The bike is a Specialized S-works Stumpjumper, 2008. Mavic CrossMax hubs and rims.

When descending/cruising, at quick speed, ONLY while either coasting or backpedaling, I get a very loud scream/rub kind of sound. It sounds a bit like something rubbing against the tire treads, except a more internal-type sound, if that makes any sense. The sound does not ALWAYs occur. And when it does, it immediately STOPS if I pedal forward.

I have checked and double checked clearances and all external rubbing -- finding nothing. No tire rub, no cables hanging close to the freewheel, derailleur is straight, etc.

It has to be something in either the hub or the freewheel. Thoughts?

Thank you.
Abrahm

[DaveM]

ratchet inside the freehub? Cassette vibrating? You might try getting some lube inside the freehub to see if it changes the sound at all. I'd also check to make sure the cassette is on tight and that the freehub is tight on the hub.

[Painkiller]

take off your plastic spoke guard behind the cassette and see if that changes anything

[cny-man]

(03-21-2014, 06:40 PM)Abrahm Wrote:  ONLY while either coasting or backpedaling, I get a very loud scream/rub kind of sound. The sound does not ALWAYs occur. And when it does, it immediately STOPS if I pedal forward.

I have checked and double checked clearances and all external rubbing -- finding nothing. No tire rub, no cables hanging close to the freewheel, derailleur is straight, etc.

It has to be something in either the hub or the freewheel. Thoughts?

Thank you.
Abrahm

No point in checking anything but the free hub or a spokeguard, as it can only be two parts that move in relation to each other when coasting.

[Joe_W]

I know that sound. I too have it on a Mavic Aksium 2009(10?) rear wheel - from time to time. It tells me that I need to overhaul the freehub body. Take a look at Mavic's tech docs, it is actually not difficult:
(read the tech doc first, also about bearing unloading / preloading, this is not needed on the older Aksiums, might be improtant for your hub, though)
- remove rear wheel
- remove QR skewer
- remove cassette
- using an Allen key (for the size: look at mavics docs), remove the freeehub body, take note which order the parts come off and watch out for the pawls that might just shoot out
- clean, then use very light oil on pawls and reassemble.

The noise is the chain going slack and rubbing against the tyre and frame, scared me a lot when I first had that! Mavic rear hubs need to be overhauled regularly, they write something like twice a year - I can get away with once per year.