Technical FAQ: Noisy Mavic freehubs
Here is some feedback on last week’s column, on “The sounds of suffering,” regarding squealing Mavic hubs. Many readers wrote in about it with a number of different theories. Here is a sample of each theory.
The problem described by the reader with the Mavic SL wheels is the dreaded “death squeal” of Mavic’s hub design. The plastic bushing Mavic uses as the inboard bearing in their freehub design wears out, and when the cassette body becomes loose, it starts to make that howling sound when freewheeling at high speed.
Tightening the cassette body helps at first, but the noise quickly returns. A longer-term fix is to replace the cassette body, but because the aluminum-bearing surface on the hub that the plastic bushing rubs against also wears, it’s a short-term fix that will repeat itself more and more often as the hub wears out.
I have no idea why Mavic thought it was feasible to use a plastic bushing instead of a real bearing in their cassette hubs, but there it is. Friends of mine who’ve tried to contact Mavic about this issue as a possible warranty item have been told it’s “normal wear and tear”.
I thought I’d jump in and explain about that inboard plastic bushing instead of a real bearing. I got the scoop on it when I was up at a Mavic 2007 MTB product intro in Whistler in July and wrote the following about it as part of a longer article for the VeloNews print magazine: Mavic has a solution for high freehub wear rate. The FTS-X freehub system retains the bushings so often complained about but reduces wear on them with harder pawls. Mavic points out that its two-pawl FTS system is a very good freehub system only in need of a bit of tweaking. It’s efficient and stiff, being a part of the hub body supported by bearings near either end of the axle, rather than being a separate part with correspondingly inboard bearing support. It is extremely simple to disassemble, clean, maintain and reassemble.
The bushing on the inboard interior end of the freehub body that riders who have had problems assume is a cheap substitute for a bearing is actually far superior to a bearing and is not the cause of freehub failure at all, according to Mavic. Loaded up to 400 kg under the pedaling force of many riders is no problem for it, as it can withstand almost a ton of load without distorting, whereas a bearing can be damaged with a 300 kg load applied to it. It’s 40 grams lighter than a bearing, and when freewheeling, there is no load on the bushing and hence no friction (and it’s as slick as Teflon to boot).
So what’s been the problem? Over the years, Mavic has upped the hardnessof its freehub bodies without increasing the hardness of the pawls, whichc an wear away and generate fine steel dust capable of grinding down the bushing. Furthermore, the thread-in axle stub can loosen up. And finally, the chain can drop onto the chainstay when freewheeling because the friction of the freehub is so high, not due to bushings or bearings, but due to a sticky lip seal.
In going from the current FTS-L system to FTS-X, Mavic has made the pawls of harder steel and applied threadlock (good for six disassemblies before applying new Loctite) to the axle end screw threads. The new pawls, being so hard, could not be forged with the little tabs to hold them inplace, so those tabs are now on snap-on plastic pieces. Mavic has also created a new lip seal made of softer material with a slick surface treatment to reduce frictional drag by 50 percent.
All of these changes are compatible with current Mavic freehub bodies,but the upgrade parts will not be available for until late next season when Mavic gets over the production hump for the 2007 wheels, all of which incorporate the freehub changes.
I had a similar noise that came from my Mavic Ksyrium freehub while coasting down the Simplon Pass last May. As you know, there are a number of tunnels on the way down to Domodossola. In the confined area of the tunnels the screeching was so loud that it sounded like my bike was going to explode!
The problem turned out to be an almost dry freehub. Removing the axle and applying a little synthetic chain lube (I did not have the mineral oil that the Mavic web site recommends) inside the freehub eliminated the screeching sound and gave me a much quieter coast. When one does this repair, one should be sure to keep an eye on the pawls and springs!
(Editor’snote: You should really clean and lube the pawls as well. You can find instructions for Mavic freehub overhaul in either ” Zinn and the Art of Mountain Bike Maintenance” book or DVD, and “Zinnand the Art of Road Bike Maintenance.”)
The problem with the Mavic SL is from the small rubber gasket in the freehub that requires occasional lube. It makes a screeching noise when freewheeling or backpedaling. The maintenance for this can be foundon the Mavic Web site.
That screeching sound is often the spring beneath the pawls in the freehub getting free and rubbing against the inside of the freehub body. I have only experienced this with the Mavic Ksyrium SLs.
It’s probably broken pawls in the freehub mechanism. I had as et of original Ksyrium SSCs. While going down a 45 mph descent last winter, they began to screech. Soon it started doing it while coasting down less steep hills, and then it progressed to making the noise whilecoasting on the flats at high speed. My local bike shop diagnosed the problem as a broken pawl. The pawls were replaced for about $15, and the wheels has been fine ever since.