Cracked DA 9000 and Ultegra 8000

Discuss light weight issues concerning road bikes & parts.
Greatestalltime
Posts: 49
Joined: Sun Jul 02, 2017 12:47 pm

by Greatestalltime

I’ve cracked my cranks on two different bikes a week apart. They are both right at one year old. DA on a Protos and 8000 on an Advanced SL. Both 172.5. Both at the same exact place on the crank about 1.5 inch from the top, right by the print. The cracks are both on the drive side and identical in every way. Except on the 8000 a large wobble accompanied the pop every down stroke.

They also both occurred at the same place. A walking/riding bridge that crosses the Ohio River. I’m guessing 8-10% grade, but may be way off. I sprint up both sides nearly every day. Usually in 52/16 or 17. I will take some pictures, but the bike shop gave me a loaner 6700 while they work on the warranty. I purchased them both from Merlin.

The guys at the shop said they’ve never seen it. Is this common? My 6700 had around 50k miles was a 170mm and I never had any problems at all.

Thoughts/ advice. I’d there a stronger crank? Should I modify how I ride? I really like attacking this this hip the way I described.

by Weenie


ooo
Posts: 769
Joined: Sat May 21, 2016 12:59 pm

by ooo

try 105 cranks (5800,r7000) they are hollow forged like 6700.
6800,9000,r8000,r9100,m9100 are hollow bonded, glued:

viewtopic.php?f=3&t=143022
'

GothicCastle
Posts: 216
Joined: Mon Jul 04, 2016 1:52 am

by GothicCastle

Cranks do fail from time to time, but two that close together must be incredibly unlikely.

Shimano is usually good about warranty replacements for things like this.

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pdlpsher1
Posts: 2270
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

Look at the bright side. You put out enough power to break cranks. You are lucky to be in the cream of crop...

If you Google you'll see many examples of cracked cranks. But since Shimano sell a lot of cranks it's hard to say what the true failure rate is. Shimano will take care of you.

Greatestalltime
Posts: 49
Joined: Sun Jul 02, 2017 12:47 pm

by Greatestalltime

Yes. They are being replaced under warranty. However, today I rode with the loaner cranks and it felt like my right pedal was bent. I wonder if I’m bending the pedals and that’s making the cranks break. I’m going to the shop tomorrow to put my DA pedals on(they’re up there)and seeing if they’re bent too.

Or I got used to the feeling of the cracked arm and now it being straight feels weird. When I took my first break in the dude that rode it said he felt a wobble that I didn’t. When the second broke I did feel the wobble.

I’m trying to figure it out and really do appreciate the suggestions and help. Thanks
The dudes at the shop said they’ve never seen it. I told my wife how strong I was and she didn’t believe me...At all.

alcatraz
Posts: 2047
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

How big a guy are you? How many years have you been riding?

During his first year riding, my 125kg friend has broken chains and bent chainrings but never a crankarm.

I think his troubles stopped after evening out his pedal stroke. Maybe do more high cadence intervals and one footed 30s intervals.

There is a difference between trying to break your stuff "powerful" and being a strong heavy sprinter.

XCProMD
Posts: 733
Joined: Sat Jan 26, 2008 10:25 am
Location: Cantabria

by XCProMD

Shimano hollow cranks do crack. They seem not wanting to issue a recall.

Of course we don’t know what the failure rate, but the risk of getting hurt is there.


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wheelbuilder
Posts: 631
Joined: Wed Feb 08, 2017 2:10 am

by wheelbuilder

I've seen 3 of these at the shop. two 8000, one 9000

Greatestalltime
Posts: 49
Joined: Sun Jul 02, 2017 12:47 pm

by Greatestalltime

alcatraz wrote:
Thu Jul 04, 2019 10:24 pm
How big a guy are you? How many years have you been riding?

During his first year riding, my 125kg friend has broken chains and bent chainrings but never a crankarm.

I think his troubles stopped after evening out his pedal stroke. Maybe do more high cadence intervals and one footed 30s intervals.

There is a difference between trying to break your stuff "powerful" and being a strong heavy sprinter.
I’m 5”10” 185. I started riding again almost 8 years ago after riding a few years when I was a teen late 80’s early 90’s.

Yeah. I guess I’ll try lower gear higher cadence. Though I never did with my 6700. Guess I’ve got to do something different. Though just last week I got some Strava top 5’s on some steep climbs in the Smokey Mountain area. So I was pretty happy with my method.
Last edited by Greatestalltime on Sat Jul 06, 2019 2:31 pm, edited 2 times in total.

TheRich
Posts: 309
Joined: Tue Jan 01, 2019 1:36 am

by TheRich

Are there any warning signs, anyone caught it before breaking?

Philbar72
Posts: 175
Joined: Tue Sep 17, 2013 9:47 am

by Philbar72

it'll ping. as in sound like a ping. thats what happened to me when my 9000 crank failed.

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kgt
Posts: 7635
Joined: Sun Jun 18, 2006 10:29 am
Location: Athens, Greece

by kgt

I had asked that before: why doesn't Shimano go for carbon cranksets to solve such issues? I am really curious.

BdaGhisallo
Posts: 2240
Joined: Wed Mar 17, 2004 1:38 pm

by BdaGhisallo

kgt wrote:
Fri Jul 05, 2019 9:47 am
I had asked that before: why doesn't Shimano go for carbon cranksets to solve such issues? I am really curious.
Because Shimano's expertise is in aluminum forging. They feel that, with their level of knowledge and the technology they employ, they can make a crankset out of aluminum that will outperform anything made from carbon. They did make a 7800 crankset in carbon in very limited numbers. The fact that they stuck with aluminum for all subsequent iterations of DA cranks tells you what they believe.

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kgt
Posts: 7635
Joined: Sun Jun 18, 2006 10:29 am
Location: Athens, Greece

by kgt

Maybe the guys at Shimano 'feel' that alu cranksets are better, but obviously they are not. Campagnolo cranksets are as stiff, lighter, sexier and without creaks and cracks. I am sure that a huge company like Shimano can start produce carbon cranksets next week if they want to.

by Weenie


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miltmaster3
Posts: 633
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Location: patra greece

by miltmaster3

Buy rotor to have your mind free


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