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Old 11-29-2007, 05:13 AM   #1
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Pissed 12GS Rear Disk Flange Cracks? UPDATE!

UPDATE 2-18-2010 "No joy in Muddville". The dealer called me after receiving a reply back from BMWNA with regards to BMW steeping up for the second flange. No surprises there, unlike the 1st flange and them saying someone must have over torked the bolts. This time it was, he did his own maintenance, the part was out of warranty, the bike could have been ridden off road, YADA YADA YADA or in plain english 'you or shit out of luck.'


While changing tires yesterday 02-16-2010, & checking the rear Disk Flange. I discovered that 2 of the lugs on the updated replacement flange had developed cracks in the same location as the flange from the original post!!!
As part of my Case for BMW to step-up and fix this problem I read all post I could find and review all picture that show Lugs with cracks or broken lugs. It appears that when the cracks are present they are all in the same general location as the ones in the picture in this post. The local dealer has shown genuine concern and I supplied them with a stack of pictures as well as my original cracked flange. I will post what ever the turnout.



Looking for any others who may have had this problem.
On the way to the Swamp Scooter’s Rally this month my rear wheel looked like it had oil spots on the rim. When I returned home I pulled the wheel to check the seal area behind it for any signs of oil. While checking I noticed that 2 of the ears of the flange that holds the disk had hairline cracks running parallel with the boltholes. The cracks penetrate all the way through to the inside of the machined threaded holes. I then cleaned the area replaced the wheel and called the local dealer explaining the problem.
The service writer asked that I bring the bike in so they could take a look at it. The next afternoon I was at the dealer so they could have a look. The service writer said that he had never seen or even heard of this problem. He informed me that he would contact BMW via a PuMA explaining the problem and asking for a recommendation. BMW responded by saying that someone must have removed the wheel at some time and over-torqued. They also said that they had not seen this before and asked the dealer if they could identify the original cause. This is not a rant about BMW not standing behind their products, it is simply a request for others that have had or seen this problem to post a reply. Most importantly it is a heads up to you guys to keep an eye on this part for any signs of a possible failure…




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AJB1 screwed with this post 02-19-2010 at 07:19 PM
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Old 11-29-2007, 06:07 AM   #2
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Strictly on an engineering/mechanical point of vue, I have a hard time to believe that over-torque is the culprit...
It is hard to speak from pictures, but the fact that bothcracks are at the same position and not in the area of minimum material thickness, would indicate a radial load.
This would occur with under-torquing and/or extreme load (i.e. braking)...
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Old 02-17-2008, 12:17 PM   #3
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Sorry I Missed This..

Quote:
Originally Posted by WildHorseRider
Strictly on an engineering/mechanical point of vue, I have a hard time to believe that over-torque is the culprit...
It is hard to speak from pictures, but the fact that bothcracks are at the same position and not in the area of minimum material thickness, would indicate a radial load.
This would occur with under-torquing and/or extreme load (i.e. braking)...
When I asked about being under tightened I had not seen this previous posting..

WHR seems to come from an engineer's point of view...any comments from the herd?

Also...I know I am grasping..but these cracks are on R12GS..what about on the Adv? Any incidents on Adv?
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Old 02-17-2008, 02:18 PM   #4
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What strikes me is that these parts are different.

The one I have is from an early bike, and the wheel bolts thread into metal inserts which are [probably] pressed in from the opposite side and run about 60% of the total width of the part. There are no bevels on either side of the rotor mounts. PN 7 668 659.

The new one has threads directly in the aluminum, bevels on the rotor side, PN 7 694 910.

The one pictured above has bevels on the non-rotor side, but I think it will be one of the two part numbers listed above. Can't tell what the OP has but it seems to have bevels on the rotor side.
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Old 02-17-2008, 02:25 PM   #5
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It would be better to have a thread insert in my opinion.

Any idea on the US cost of this part Anton?
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Old 02-17-2008, 02:29 PM   #6
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Quote:
Originally Posted by Desert Skies
It would be better to have a thread insert in my opinion.
Well, the only one that I have seen fail had the insert.

Quote:
Any idea on the US cost of this part Anton?
$226. The version with inserts is obsolete, which is probably a good thing.
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Old 02-17-2008, 02:32 PM   #7
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A wild guess holes tapped by worn tap, or oversize bolt.
No sign distortion, or crud in holes, any one have access thread gauges or optical comparator for bolts?
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Old 11-23-2011, 06:24 PM   #8
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Quote:
Originally Posted by WildHorseRider View Post
Strictly on an engineering/mechanical point of vue, I have a hard time to believe that over-torque is the culprit...
It is hard to speak from pictures, but the fact that bothcracks are at the same position and not in the area of minimum material thickness, would indicate a radial load.
This would occur with under-torquing and/or extreme load (i.e. braking)...

Agreed, over torquing of the bolts is not likely the culprit. I don't understand why people are so attached to that being the cause when all the pictures of this failure show no signs of thread damage and it has been stated that the failure has occurred on bikes that have manufacturer installed rotors. One thing that has not been reported consistently is if the bikes had ABS or not. My bike with almost a 100k mi., 3rd rotor, no ABS has not had this issue, yet. *knocking on wood*

I will now ask a few questions about rotor mounting and why would it be mounted that way. Think about for yourself for a bit before jumping to reply.

- What happens to an iron ring when it is heated?
- What stresses would be applied to the mount if the ring were solid mounted as BMW has seen fit to do?
- Why or what are the reasons for a floating disc?
- Why are BMW front discs of the floating design and the same on most all performance bikes (both front and rear) and performance upgrades?
- Have you seen the design that Harley Davidson came up with on their standards to deal with a hot solid mounted ring and how is it different than BMW's?
- What effects does ABS have in regards to the heating and wear of the rear disc?

These are all factors that should considered during the design phase of a part.

In my many decades of fabricating, building and repair of wheeled things BMW's engineers plain and simple dropped the ball with this design. IMHO
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Old 11-23-2011, 07:06 PM   #9
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Overtorquing of the rotor bolts is a non-issue. There MAY be SOME truth, in part, to overtorquing of the wheel bolts. However, there are two different issues here.

First are the rotor holes cracking. Second are the wheel bolts cracking. BOTH are solid mounted. IMHO, being solid mounted has nothing to do with the issue. Innapropriate design by material or form is the issue.

Jim
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Old 11-25-2011, 10:01 AM   #10
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SO on my 04 BMW 1200 GS, 36000 or so miles. BMW picking up the tab to fix the flange... Hurrah! From dealer quoting 1100 pounds to BMW picking up the tab.
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Old 03-15-2012, 05:11 AM   #11
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Quote:
Originally Posted by WildHorseRider View Post
Strictly on an engineering/mechanical point of vue, I have a hard time to believe that over-torque is the culprit...
It is hard to speak from pictures, but the fact that bothcracks are at the same position and not in the area of minimum material thickness, would indicate a radial load.
This would occur with under-torquing and/or extreme load (i.e. braking)...

Has anyone considered the possibility that thermal expansion of the non-floating brake disc is pulling the bolts outward radially and causing cracks? I would expect a torque induced crack to be in the direction of rotation, not radially as in the OP photo. Using the term radially in the engineering sense, ie. out word from a center point in a straight line.
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Old 11-29-2007, 06:14 AM   #12
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This is the first insantance of this posted here. Are those holes where the wheel bolts fasten to? If so, is it possible that someone over torqued the bolts when installing the wheel?
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Old 11-29-2007, 06:36 AM   #13
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It's the rotor bolts. Can you show us a picture of the other side? Almost looks like one of the bosses has a flat spot in it, although it might just be the lighting.
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Old 11-29-2007, 06:38 AM   #14
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Quote:
Originally Posted by Gadget Boy
This is the first insantance of this posted here. ...
+1, this is a new one on me, and hopefully, an isolated incident!

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Old 11-29-2007, 09:16 AM   #15
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Are you the first owner? If you are, has anyone removed the rear rotor since you bought it? And I'm afraid to ask, but what does that part cost to replace?
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