12GS Rear Disk Flange Cracks?

Discussion in 'GS Boxers' started by AJB1, Nov 29, 2007.

  1. AJB1

    AJB1 Retired

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    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…



    [​IMG]
    #1
  2. WildHorseRider

    WildHorseRider Adventurer

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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 both cracks 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)...
    #2
  3. GB

    GB . Administrator

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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?
    #3
  4. AntonLargiader

    AntonLargiader Long timer

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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.
    #4
  5. JimVonBaden

    JimVonBaden "Cool" Aid!

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    +1, this is a new one on me, and hopefully, an isolated incident!

    Jim :brow
    #5
  6. GB

    GB . Administrator

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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? :ear
    #6
  7. michnus

    michnus Lucky bastard

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    In South Africa the equivalent of $315, check those splines they get worked out after a while.
    #7
  8. Gimpinator

    Gimpinator This is my Mom's cat

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    I can't imagine the rotor bolt would be the only culprit. You really can't get a whole lot of torque on those without rounding the socket.

    Perhaps the rear brake was dragging? Any signs of discoloration on the other side of the part? Any blueing or heat checking on the rotor?

    That's a strange one!
    #8
  9. rideLD

    rideLD The further the better!

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    This makes the most sense to me.

    I also have never seen this before but it does have me wondering if any of the "lack of oil in the FD related failures" could have been caused by those cracks? :ear
    #9
  10. AJB1

    AJB1 Retired

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    Gadget Boy,
    The holes are where the disk mounts to the flange. The disk would be flat on the other side.
    <o:p></o:p>
    AntonLargiader,
    Flat spots, you are correct, it is just the light.
    <o:p></o:p>
    Gadget Boy,
    I am the only owner and no the disk has never been removed or re-tourqued.
    <o:p></o:p>
    Michnus,
    It wasn’t cheap, $234 after a 20% discount. The dealer felt sorry for me when he saw the list price.
    <o:p></o:p>
    Gimpinator,
    The rear brake is fine, no dragging no discoloration.
    <o:p></o:p>
    RideLD,
    <!--[if !supportEmptyParas]--> <!--[endif]--> <!--[if !supportEmptyParas]--> <!--[endif]--> <!--[if !supportEmptyParas]--> <!--[endif]--> <!--[if !supportEmptyParas]--> <!--[endif]--> <!--[if !supportEmptyParas]--> <!--[endif]--> I can’t imagine that the amount of oil in the final drive could affect these lugs.
    #10
  11. AntonLargiader

    AntonLargiader Long timer

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    Thought I'd mention that I've seen a similar case. I'm pretty solidly convinced it's from overtightening; in this case it's the wheel lugs rather than the brake rotor bolts. All five show the same crack:

    [​IMG]

    If this (or the previous example) had been caused by an external force, I'd think that the part would have broken away once the crack happened. Overtightening, the force was relieved once the crack occurred.

    It initially seems like a dangerous failure mode, but when it comes down to it neither part failed in use after the crack happened, so the flange is strong enough for its task even with the crack there. OTOH it's hard not to think that the part might not crack with another millimeter or two of material there.

    This might be a good one-time inspection item for people who don't know the full service history of their bike.
    #11
  12. GB

    GB . Administrator

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    Thanks for the heads up Anton..

    I don't have my torque values in front of me, but what is the correct torque value for the bolts holding the rear wheel to the flange? :ear
    #12
  13. AntonLargiader

    AntonLargiader Long timer

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    Good point. 60 Nm for the wheel, 30 Nm for the rotor. Work up to it incrementally, in a star pattern in either case.
    #13
  14. GB

    GB . Administrator

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    Thanks Anton! And one more thing: Apply the bolts DRY!! NO Loctite, or anti seize compound.
    #14
  15. Wallowa

    Wallowa Long timer

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    Anton....dumb question, but if a bolt is not torqued enough, could that generate enough movement/shock to fracture a flange?
    #15
  16. AntonLargiader

    AntonLargiader Long timer

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    I don't know, and can't really set up a valid test for that. However, the overtightening part will be easy to test with the brake rotor bolts. I'll let you know how that goes.
    #16
  17. JimVonBaden

    JimVonBaden "Cool" Aid!

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    While it is certainly possible that low torque could cause it to crack, it is unlikely for two reasons.

    One, too loose and the bolts vibrate loose and the wheel comes off.

    Two, 60nm is not much torque, and it is far more likely that someone over torque it than under torque it when not using a torque wrench!

    Jusy my humble opinion. Now, I am off to take a look at mine, and my fork tube pinch bolts!:deal :uhoh

    Jim :brow
    #17
  18. Wallowa

    Wallowa Long timer

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    That makes sense and too loose will oblong the holes..
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  19. Desert Skies

    Desert Skies One brick shy...

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    Didn't want to feel left out. Had the wheel off so I inspected the bosses and not to my supprise, looky what I found.

    [​IMG]
    #19
  20. Wallowa

    Wallowa Long timer

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    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?
    #20