Saturday, May 1, 2010

How Not To Design A Freehub

A couple of weeks ago, after climbing up the steep switchback on Myrtle here in West Seattle, I stopped to wait for traffic, and then tried to start again. The cranks spun freely, not engaging anything, as if I had dropped my chain. But my chain was still in place. Turns out the pawls on my freehub were not engaging the hub shell.

When I removed the freehub, this is what I found. Unlike the other freehubs I've examined, in which each pawl is pushed up against the shell with its own spring, this hub had all the pawls held in place and tensioned with a single spring. The springs sits in the groove that goes around the circumference of the freehub base. That spring had broken in two places.

The result was complete failure with no warning. With other hubs I've owned, as each pawl failed, it led to a decrement in performance (e.g., skipping), which gave me a warning that something was wrong, but let me get home.

The hub is branded Velocity, and it's one of the very, very few sub-$350 130mm disc hubs on the market. (Why oh why didn't I invest in that Chris King? Will I never learn?). I can barely navigate through the Velocity website, much less find a replacement spring.

I've e-mailed Velocity -- we'll see if they can get me a replacement.

If not, I'm going to try to fabricate a replacement spring. I bought a couple of different kinds of spring wire, and I'll try shaping the wire and curing it in my oven at its highest temperature. If that doesn't work, I may ask Seattle Pottery Works to fire it in one of their kilns.

If the fabrication experiment doesn't work, I may try to fit in traditional independent pawl springs -- I think there's enough room in the indentation.

1 comment:

Chad said...

That sure does sound like an interesting project. Let us know how it goes.

How did you get home? Riding your bike scooter style?