Go Back  Bike Forums > Bike Forums > Tandem Cycling
Reload this Page >

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

Notices
Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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

Old 03-08-21, 01:08 PM
  #1  
sapporoguy
Senior Member
Thread Starter
 
Join Date: Mar 2015
Location: San Francisco
Posts: 121

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

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 49 Post(s)
Likes: 0
Liked 20 Times in 9 Posts
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.
sapporoguy is offline  
Old 03-08-21, 04:22 PM
  #2  
Alcanbrad
Senior Member
 
Alcanbrad's Avatar
 
Join Date: Apr 2015
Location: New Jersey
Posts: 356

Bikes: '14 CoMo Carrera, '11 CoMo Primera co-pilot, '98 Santana Visa, a Plethora of road bikes, A commuter/Gravel beast (and 1 MTB)

Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 87 Post(s)
Liked 30 Times in 26 Posts
It's hard to see much detail as the pictures are very small, but given the symmetric failure points right where the body of the adapter changes radius makes me wonder if there is a stress concentration situation going on. Is there evidence of cracking at the 4 and 10 oclock position of the second picture? Additionally, if the donut is aluminum there may be some galvanic corrosion coupled with a stress concentration that could weaken the metal.

Can you post larger pictures?
Alcanbrad is offline  
Old 03-09-21, 09:53 AM
  #3  
sapporoguy
Senior Member
Thread Starter
 
Join Date: Mar 2015
Location: San Francisco
Posts: 121

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

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 49 Post(s)
Likes: 0
Liked 20 Times in 9 Posts
Originally Posted by Alcanbrad View Post
It's hard to see much detail as the pictures are very small, but given the symmetric failure points right where the body of the adapter changes radius makes me wonder if there is a stress concentration situation going on. Is there evidence of cracking at the 4 and 10 oclock position of the second picture? Additionally, if the donut is aluminum there may be some galvanic corrosion coupled with a stress concentration that could weaken the metal.
Can you post larger pictures?
Here you go. Let me know if you want still bigger or other angles. No cracking at 4 and 10. It does appear to be aluminum. Thanks.


sapporoguy is offline  
Old 03-09-21, 10:42 PM
  #4  
LV2TNDM
Senior Member
 
Join Date: Apr 2005
Location: Northern CA
Posts: 526

Bikes: Cannondale tandems: '92 Road, '97 Mtn. Mongoose 10.9 Ti, Kelly Deluxe, Tommaso Chorus, Cdale MT2000, Schwinn Deluxe Cruiser, Torker Unicycle, among others.

Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 148 Post(s)
Liked 93 Times in 61 Posts
Originally Posted by sapporoguy View Post
I'm posting in case it helps anyone.
...snip...
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.
I'm not sure how the prior owner could have "over-torqued" it. Isn't it simply tightened every time you slam on the rear brake? That thing must get INCREDIBLY tight. And it seems to me no set screw would be able to counter the torque forces created by the rotor.

The incorporation of wrench flats on that donut appear to be its Achilles heel. Dumb to reduce the thickness on something that sees so much force. That sure looks to me to be the reason it cracked in two. Shoulda forgone the wrench flats and simply utilize the rotor bolts for removal. It would require some tooling, but that seems like a much better way in the long run. Or utilize titanium or another material with higher strength.
LV2TNDM is offline  
Old 03-10-21, 09:59 AM
  #5  
sapporoguy
Senior Member
Thread Starter
 
Join Date: Mar 2015
Location: San Francisco
Posts: 121

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

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 49 Post(s)
Likes: 0
Liked 20 Times in 9 Posts
Originally Posted by LV2TNDM View Post
I'm not sure how the prior owner could have "over-torqued" it.
I meant: overtorqued the disc-mounting bolts. The cracks are in the thinnest point right there at the bolt holes.
sapporoguy is offline  
Old 03-11-21, 12:32 AM
  #6  
LV2TNDM
Senior Member
 
Join Date: Apr 2005
Location: Northern CA
Posts: 526

Bikes: Cannondale tandems: '92 Road, '97 Mtn. Mongoose 10.9 Ti, Kelly Deluxe, Tommaso Chorus, Cdale MT2000, Schwinn Deluxe Cruiser, Torker Unicycle, among others.

Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 148 Post(s)
Liked 93 Times in 61 Posts
Originally Posted by sapporoguy View Post
I meant: overtorqued the disc-mounting bolts. The cracks are in the thinnest point right there at the bolt holes.
Oh, I see. Possibly, but I doubt it. Either way, that design is flawed and it's too bad they made the walls so thin on either side. Bummer.
LV2TNDM is offline  
Likes For LV2TNDM:
Old 03-12-21, 01:02 PM
  #7  
sapporoguy
Senior Member
Thread Starter
 
Join Date: Mar 2015
Location: San Francisco
Posts: 121

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

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 49 Post(s)
Likes: 0
Liked 20 Times in 9 Posts
OP here. Just to add: After swapping in the new disc donut, the bump-bump-bump was gone when I bedded in the sanded disc and pads.
sapporoguy is offline  
Old 03-12-21, 07:08 PM
  #8  
Alcanbrad
Senior Member
 
Alcanbrad's Avatar
 
Join Date: Apr 2015
Location: New Jersey
Posts: 356

Bikes: '14 CoMo Carrera, '11 CoMo Primera co-pilot, '98 Santana Visa, a Plethora of road bikes, A commuter/Gravel beast (and 1 MTB)

Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 87 Post(s)
Liked 30 Times in 26 Posts
Originally Posted by LV2TNDM View Post
Oh, I see. Possibly, but I doubt it. Either way, that design is flawed and it's too bad they made the walls so thin on either side. Bummer.
I agree, I think it is a stress concentration at that point.

Sapporoguy, you might want to pick up a second adapter and have it in your stash of bike parts. It is fails again in the future, you might not be able to find a replacement.
Alcanbrad is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.