Old 03-08-21, 01:08 PM
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sapporoguy
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Join Date: Mar 2015
Location: San Francisco
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Bikes: 2000 Santana Sovereign SE; 2005 Co-Motion Speedster; Kona Kilauea with various dorky commuter accouterments; Mercier Kilo TT fixie; Burley Fladbed trailer for groceries

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Cracked DT Swiss Hugi screw-on 'disc donut' replacement pix

I'm posting in case it helps anyone.
The bike: 2005 Co-Mo speedster, rear disc brake, DT Swiss Hugi hub with threading for Arai drum or disc adapter.
I'd noticed a bump-bump-bump when braking. Finally took a closer look and found this crack and another halfway around:


with disc off, cracked at bolt holes, 2 o'clock and 8:


Fortunately, Mel at Tandems East makes and sells these: DT Hugi Disc Rotor Screw On 145 (20mm wide), $44, aka the "disc donut."
Ordered by email. Mel phoned with advice: Check if there's a set screw and turn it out first, or you'll damage the threads; check threads for damage and use a thread chaser such as a same-sized nut if they are; use never-seize when putting the new donut on.

I screwed the old donut off just a bit, and it did this (a bit alarming!) all on its own:


I had no set screw, the threads were clean and I used never-seize on the shiny new donut:


I wonder why the failure. Fatigue? Material failure? Over-torqueing by prior owner (not me!)?
In any case, thanks to Mel for the quick solution.
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