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Old 02-04-12, 08:31 PM   #1
Mr. Hobbes
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Internal brake cables = eventual catastrophic failure?

Last week my beautiful steel triple-butted Miyata 914 went all wobbly on me as I stood up out of the saddle to pass a fellow cyclist. I was able to recover and slow down enough to see that my top tube had cracked completely through and had become detached right where you would expect it to — towards the front end where the hole is drilled for the rear brake cables. Is this a common occurrence with steel bikes that run the cables through the frame? In retrospect it seems like a pretty obvious design flaw to me since the hole is drilled right where the torque/normal wear and tear on the frame seems like it would be greatest.

Or is this more of a freak occurrence?


Comments? suggestions? Are these frames safe? or am I dangerous and guilty of abusing them?

Last edited by Mr. Hobbes; 02-04-12 at 09:21 PM.
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Old 02-04-12, 08:35 PM   #2
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Had that happen to an experimental fork after 13,000 miles.
Two holes in fork blade to run computer cable internally (that's before wireless 'puters).
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Old 02-04-12, 08:35 PM   #3
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First I've heard.

My Paramount is internal, but there are external pieces brazed on. Probablly stronger there.
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Old 02-04-12, 08:51 PM   #4
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I don't think I ever heard of it either. as Robbie points out most bikes are reinforced in some way and the entrance/exit holes


OH yess Pics or did not happen
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Old 02-04-12, 09:04 PM   #5
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Quote:
Originally Posted by Mr. Hobbes View Post
...or am I dangerous and guilty of abusing them?
Only you can answer that - and there is nothing in your post that describes anything approaching abuse

Was there any damage prior to this incident? If you look 'round the various Forums you'll see examples of catastrophic failures that may/may not have been precipitated by an earlier collision. Do you know the complete history of your Miyata?

Glad you didn't end up doing a face-plant - or worse

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Old 02-04-12, 09:12 PM   #6
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I recall Miamijim mentioned a flaw in the Miyata design. Later models had gussets reinforcing that area. Thought the 914 was after that era. Hopefully Jim will wade in, or do a search.

Did your bike have gussets in that area?


Found it:

http://www.bikeforums.net/showthread...iyata-cracking

Last edited by wrk101; 02-04-12 at 09:27 PM.
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Old 02-04-12, 09:17 PM   #7
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Quote:
Originally Posted by Bianchigirll View Post
I don't think I ever heard of it either. as Robbie points out most bikes are reinforced in some way and the entrance/exit holes

Steel triple-butted Miyatas with internal routing do not have any braze-ons or any other kind of reinforcement where the top tube is drilled for the cables. All they have is a rubber plug that seals the elliptical hole where the cable is routed.



Quote:
Originally Posted by Bianchigirll View Post
OH yess Pics or did not happen
OH yess, it happened...but I already removed the cranks and the headset and tossed the evidence in the dumpster - after bending the top-tube out of place so that it would not be salvaged (unless someone finds it who wants to replace it.)
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Old 02-04-12, 10:22 PM   #8
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How were the elliptical holes made on the TT? were they punched out or cut out by the factory. Just wondering how much stress they put on the material doing it. Maybe punching it out could produce micro cracks along the edges that eventually could get bigger from stresses caused by riding??

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Old 02-05-12, 05:34 AM   #9
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Quote:
Originally Posted by Mr. Hobbes View Post
Steel triple-butted Miyatas with internal routing do not have any braze-ons or any other kind of reinforcement where the top tube is drilled for the cables. All they have is a rubber plug that seals the elliptical hole where the cable is routed.
The initial run of bikes didn't have re-inforcing gussetts, upon learning of the cracks Miyata made a running change in production and added gussetts. Depending on when a dealer oredered inventory both un-reinforced and reinforced frames could both be on the showroom floor. There was no recall and frames were replaced at no cost to the owner as needed. 712's were most affected but then again we sold more 712's than any other internal cable routed model.

I could do a frame swap in 30 minutes or less.



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Old 02-08-12, 05:42 PM   #10
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Heard about that before, and I know one example with pictures. BF member liquefied posted a picture of his 1989 Team that I believe had the same issue. Reposted here from the "Can I see your Miyata" thread.

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