# Noise Only While Coasting



## JasonB176 (Aug 18, 2011)

Three rides ago I heard a grinding/scraping sound suddenly while coasting on a descent. I stopped the bike thinking something was wrong with the wheels. I couldn't find anything. When it happened again, I took note that it was coming from the area where the cranks enter the frame, the bottom bracket I guess.

The next ride in warmer temperatures it didn't happen at all. Today in colder temperatures it kept happening a lot. I may have imagined it but I thought I could detect a bit of a burning smell.

I'm totally confused as to what could be causing such a noise only while the bike is coasting. I would have thought it would have been the other way around. Could this be something to do with the bearings in the bottom bracket? I know very little about the mechanical side of things. It's my 2000 Specialized which has never been serviced in that area.

Any tips or advice would be greatly appreciated!


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## bikerjulio (Jan 19, 2010)

I can only think of a freehub problem, not BB.

Secondly a wheel bearing.

Wheels are straight and not rubbing at all?

Sounds like you need to see an expert.


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## JasonB176 (Aug 18, 2011)

bikerjulio said:


> I can only think of a freehub problem, not BB.
> 
> Secondly a wheel bearing.
> 
> ...


No rubbing with the wheels. What's confusing me is that if it was a wheel problem, wouldn't I hear the noise when I'm pedaling also? The bike seems to ride perfectly fine while I'm pedaling. I don't notice anything being different.

I'm planning on bringing to my LBS but was hoping someone would perhaps know how it's possible that a noise would only occur while the bike is coasting. It didn't seem to happen at very low speeds but anything over 20, and it kept happening.


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## bikerjulio (Jan 19, 2010)

Well, a freehub problem will only show up when coasting. Hence my #1 diagnosis.


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## mikerp (Jul 24, 2011)

When was your freehub serviced last? Temperature can easily be linked to grease.
In regards to coasting it would have anything to do with the freehub to wheel interfaces.

Example of a coasting issue
I ran into an issue with Powertap G3 hubs and Campy builds, 1st cog was rubbing DS spoke during cornering (coasting), the rub would cause some chain slap on the stay when things touched. Saris had seen the tolerance stacking issue and supplies a spacer when it comes up.


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## JasonB176 (Aug 18, 2011)

I'm sorry, I'm truly ignorant about many of the mechanical things in cycling. I'm not sure exactly what the freehub is. Is it on the front wheel without the drivetrain? These are both new wheels, less than a year old. Ksyrium Equipes.

I got them just before last winter and rode them throughout the cold weather last year without any issues.


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## JasonB176 (Aug 18, 2011)

Ok, wikipedia gave me a basic overview of what a freehub is. So because it's only happening while I'm coasting, it would seem this is the problem. A bearing issue? I'm just surprised as I've had other Mavic wheels go much longer without issues. 

This is my beater bike so it has been exposed to many wet and/or salty rides. I always cleaned it after every ride though.


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## VCRC Bike (Jul 1, 2009)

You need to service your freehub. Mavic recommends doing this every 1500 miles or so (I believe, something around there though). Pull the freehub, lube the pawls and the plastic bushing with oil, re-install and the problem is fixed!


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## JCavilia (Sep 12, 2005)

The freehub is the mechanism on the rear wheel that allows you to coast. It lets the wheel turn without the cassette (the gears in the back) turning. Noises that appear only when coasting are usually related to the freewheel, though sometimes they can be from elsewhere, but are masked by other sounds when you're pedaling. 

As for the sound seeming to come from the bottom bracket, bicycles are notorious for transmitting sounds through the structure, to fool you about where they come from.

I agree with the suggestion to have someone look at the freehub.


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## bikerjulio (Jan 19, 2010)

VCRC Bike said:


> You need to service your freehub. Mavic recommends doing this every 1500 miles or so (I believe, something around there though). Pull the freehub, lube the pawls and the plastic bushing with oil, re-install and the problem is fixed!


OP is not mechanical, and did not even know what a freehub was until 2 mins ago. So this advise, though correct in general, might not be in the case of our OP.


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## JasonB176 (Aug 18, 2011)

Thanks everyone. I plan to take it in tomorrow and I appreciate having the foreknowledge that it's most likely a freehub issue.

I don't have the faintest idea how difficult it would be to service this myself. I'm pretty sure it would be way over my head but I may look into it for the future. 1500 miles isn't very much though!

Could it be the exposure to cold and wet (even snowy) riding has caused this to be an issue at what seems to me to be very soon? My better bikes I never ride in the wet intentionally and have never had this problem.

ETA: I'm curious, is this a safety issue? I was somewhat unnerved during my ride today and tried hard to limit my coasting. Could something catastrophic theoretically have occurred while I coasted down hills?


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## bikerjulio (Jan 19, 2010)

Actually yes - it could become a safety issue if your rear wheel was to suddenly lock up while coasting.


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## Kerry Irons (Feb 25, 2002)

JasonB176 said:


> Thanks everyone. I plan to take it in tomorrow and I appreciate having the foreknowledge that it's most likely a freehub issue.
> 
> I don't have the faintest idea how difficult it would be to service this myself. I'm pretty sure it would be way over my head but I may look into it for the future. 1500 miles isn't very much though!
> 
> ...


Just so you know, this is an "undocumented feature" of MAVIC hubs. IOW it is a crappy design, relying on a nylon bushing instead of bearings at the interface. "MAVIC howl" is a well-known phenomenon. If you don't get it lubed it could eventually seize, though it would get very nastily loud as it approached that point.

Once you see it done and have the proper large Allen wrench it is a pretty easy job. You can find videos on how to service MAVIC hubs. Since cold makes things contract you probably are experiencing some tolerance issues that may diminish with time as the plastic bushing wears.


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## Guest (Nov 9, 2013)

Possibly a wheel is out of trueness and it's rubbing on the brake or the brake is just tweaked to the side and rubbing.


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## JasonB176 (Aug 18, 2011)

*Fixed*

It was indeed the freehub. My LBS did the servicing and said it was definitely in need of it as water had entered and caused damage. I tested it and it appears to be perfectly quiet now. $25, not too bad.

I think that answers my question about the exposure this bike receives as being part of the problem. Supposedly it's a sealed hub but water found a way in. A yearly $25/maintenance for the rear wheel of my beater bike is acceptable though I wonder if another brand of wheel would have stood up better. Most likely given Mavic's reputation.

Thanks again guys. It helped that I could go in and tell them what the issue was. Otherwise I would have been leading them astray talking about the bottom bracket.


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