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Thread: Speedometer Problem Solved!

  1. #1
    Registered User rocketmanli's Avatar
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    Speedometer Problem Solved!

    I spent almost 4 weeks chasing down electrical gremlins as the possible cause for the speedometer suddenly not working on my 2002 R1200C. Sent out the speedometer for testing; swapped out the speedo sensor cable on another bike, and everything tested fine. Removed and opened up the miles of spaghetti that makes up the speedometer harness looking for broken grounds, shorts, etc. Pulled fuses and relays from the electrical junction box. Called everyone I knew, and some folks I didn't know looking for advice. After all that time and aggravation, it turned out that an $11.00 part, known as an Impulse Sending Wheel, had actually somehow come loose from the crown gear shaft inside the final drive. It was held onto the shaft loosely by the tapered bearing, so it didn't go anywhere, but it caused no impulses to be created with the wheel rotation, and therefore, no speedometer working. I brought the parts to my local welder and had the impulse wheel welded to the crown gear shaft, never to come off again (I hope!) Lesson learned...always look for the easiest, most obvious mechanical issues that could be a cause-and-effect item, before delving into the never ending, process of elimination electrical nightmares that newer bikes offer. Of course after losing endless hours of sleep for the past month, I did a search for "Impulse Sending Wheel" on this site today, and found the exact same problem, only mentioned once, back in 2007. Had I looked here first, I would have been riding for the past month, instead of dissecting my bike. 2nd lesson learned.
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    Are you familiar with Chromeheads.org?

  3. #3
    Registered User rocketmanli's Avatar
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    Yes. I'm one of the Moderators there. The help of our members was invaluable in solving my unusual problem.

  4. #4
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    Another fine example of BMW engineering gone amok. There is just no good reason to design this way. (other than you can).
    '03 R1150R, '03 F650GS, '97DR200SE,'78 Honda CT-90, '77Honda CT-90

  5. #5
    Registered User rocketmanli's Avatar
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    As obvious as it is now, that would have been the last thing I would have suspected. And one would think that tiny, little wheel would be attached pretty well, since its rotating with every spin of the wheel, at some major rpm's, for ever and ever, sloshing around in warm to hot gear oil. But noooooo! Its just like pressed on by hand, and its supposed to stay put. That's why I had it welded back on. Short of going back to a normal external speedometer cable, which generally worked pretty well over the history of motorcycles, I can't fathom what an afterthought this feat of engineering was. I just hope my experience helps someone else out down the road to save some time and aggravation. I'm told this same impulse wheel is found our BMW C's and CL's, but also K1200RS, R1100S, K1's, K100RS, K1100LT, K75's and K100's. Cruisers actually have something in common with other bikes, for a change!

  6. #6
    . AntonLargiader's Avatar
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    I wouldn't really consider ~1000 RPM major.

    It's a problem that very occasionally has happened on all models with that setup. It sure isn't perfect, but I'd much rather have that than have a mechanical speedo cable which was the only alternative design at the time.
    Anton Largiader 72724
    largiader.com bmwra.org

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