2013 F800GT rear abs sensor ring - BMW F800 Riders Forum & Registry



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  1. #1
    Kathy2013's Avatar
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    I have a 2013 F800GT with 28k. I bought at 15k. At 26k my rear sensor ring broke. We replaced it. Now, at 28k, it broke again. Some history: we ride slow speed maneuvers and I do trail brake in twisties. But, no more than any other rider. My pads are new, brakes are not hot or squeeling. We changed the sensor with the last ring, just in case. Does anyone have an idea of how the ring is breaking? Here are pics of the first ring, and the current broken ring still on the bike.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  3. #2
    Kathy2013's Avatar
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    Here is the second pic
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  4. #3
    WildWilly's Avatar
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    Can't help you with your question but the knowledgeable folks here will. Welcome to the forum.
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  6. #4
    Richard230's Avatar
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    Welcome, Kathy. I can't say that I have seen anything like that before. I don't know what would cause the sensor ring to break like that.
    Richard - Current bikes: 2016 BMW R1200RS, 2018 16.6 kWh Zero S, 2011 Royal Enfield Bullet 500 Classic, 2009 BMW F650GS, 2020 KTM 390 Duke, 2002 Yamaha FZ1 (FZS1000N) and a 1978 Honda Kick 'N Go Senior. 

  7. #5
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    I'll suggest a rock or road debris getting jammed between the ring and a non-moving part of the motorcycle.
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  8. #6
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    Welcome, I have a 2016 F800GT with 24,000 miles. Bought with 4,700 less than 2 years ago. Most of my riding has been long trips and I don't use the rear brake much.

    In first pic, to the right of the mounting hole is that a crack? To have one break is unusual IMO but 2 in less than 10K is quite unusual. I see some discoloration around the mounting points. When installing new one were the surfaces checked to make sure they were clean and free of rust and debris? The sensor rides close to the ring but is pretty well protected and I expect road debris would have a hard time getting in there to damage the ring. Check the rotor to make sure it is true, check the brakes check wheel mounting etc. I would be looking for side to side movement particularly with the brake disk. Are the brake pads properly positioned? i.e. do they clamp the disk properly - I'm thinking possibility of a missing shim causing the pad to put more pressure on one side of the disk than the other. But that seems to be a stretch to cause your problems.

    Curious as to what you determine.

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  10. #7
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    Looks like either extremely bad luck or something on the bike is too close to the ring and hitting it.

    On the other hand, the intervals are pretty long for damage from a part that's too close.

    My advice would be to get a 3rd ring (preferably used as a new one isn't exactly cheap) and check periodically for any sign of damage.

    For the record, I've never heard of abs ring damage like that.

  11. #8
    Kathy2013's Avatar
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    Thank you all for your response. We have ruled out debris because it is only hitting one "tooth", that would have to be a very fast event to break only one. We are also thinking it has nothing to do with trail braking or slow speed maneuvers, but rather high speed wheel spin. A stress from something?

    PhotoAl - these are definitely things we will look at when taking it apart....again. We did notice after looking at the pics again that it is the same "tooth", third to the left of that mounting bolt. We will check for that stress crack when we tear it down. I don't remember seeing one.

    Thanks all for different views, other things to check ....will keep you posted, if we ever determine the cause😊

  12. #9
    Albervin's Avatar
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    I also do a lot of trail braking on hairpins etc. My biggest gripe is brake dust on the rear wheel. To break a rim like this requires either a big force, which surely you would feel, or a consistent light force. As it is a very specified point I would be looking at an "out of round" situation. What about the brake disc? Has the bike been in an accident at any time? There must be another mark somewhere that has caused this. This is a case for forensic investigation. Take the wheel off, get a small bright LED torch and take your time.

  13. #10
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    you might have a bad bearings, take the calipers out and if you have a center stand check if your wheel has a play. I have this happened to my f800st and the culprit is bad bearing.

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  15. #12
    Kathy2013's Avatar
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    We did replace the disc and, of course, the sensor ring. No play, bearings good, torqued everything to spec, as we always do. No other damage anywhere, no marks from this breaking, other than that piece missing and abs stays on. Time will tell if it was the disc. Both times have happened during cone/slow speed practice which I have done since day one of owning this bike, over 10k miles before this issue started. Thanks for all the input!

  16. #13
    Kathy2013's Avatar
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    Quote Originally Posted by doyninja View Post
    you might have a bad bearings, take the calipers out and if you have a center stand check if your wheel has a play. I have this happened to my f800st and the culprit is bad bearing.
    Hi doyninja, did you say this same thing, sensor ring broken, happened on your ST?

  17. #14
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    I feel like I am a pretty good mechanic, and I have been around bikes for a very long time. I keep trying to imagine what could cause this breakage, I have looked at my bike to see all the parts involved, and I don't have a clue.

    While I could see that a stone or a hard piece of debris could cause it....the chances of it happening twice are a bit obscure.

    There is nothing about your riding style that would cause this failure - and the ring should not fail in this matter. Not once - and certainly not twice!

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  19. #15
    Right Hand Drive's Avatar
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    I also looked at my bike and the only thing that comes even close to the rotating sensor ring is the sensor itself. Was there any damage to the old sensor when you changed it? I also wondered, perhaps the hub mounting points for the ring, either side of the damage are not aligned flat so that when you tighten down the ring there is some tension in it, eventually causing a fracture. Seems strange though that the ring was ok for 11k after you bought the bike then the replacement ring fractured in 2k. Any change in riding style after the ring was replaced? I do agree with Thumpin though, riding style shouldn't make any difference and the likelihood of 2 stone impacts in exactly the same place has got to be very low.
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  20. #16
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    As PhotoAl remarked in post #6, there appears to be a crack in ring near mounting lug. May be there is distortion in ring or hub subjecting ring to abnormal load when tightened and eventually leading to a fatigue crack?
    There is no sign of abrasion on face of perforated portion of disc which suggests to me failure was not due to impact with a stone or the sensor.

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