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  1. #1
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    Unusual front airbag deployment.

    Has anyone ever heard of both front airbags going off while just driving down the road? Both front airbags plus the driver's seatbelt tensioner deployed today on my son's '98 2.8 while he was cruising down the highway at 70 mph (smooth, straight road, perfect weather). The guibo broke (it was only 1 year old), so I'm sure that's what triggered the airbags, buy why?

    This same car hit a deer at 50 mph (no deployment)4 years ago and also hit a truck tire tread at 70 mph (no deployment) 2 years ago. Perhaps this was just a delayed reaction to those incidents.

    vc

  2. #2
    Robert Platt Bell
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    Sensor above shaft tunnel?


    I am not sure about the Z3, but on my E36 cabrios there is a crash sensor (rollover sensor?) under the back seat, right above the drive shaft hump. Perhaps the Z3 has one in a similar location?

    Perhaps when the guibo broke, the drive shaft whacked the hump, causing an instantaneous acceleration reading that triggered the airbags?

    Just a thought...

  3. #3
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    You are correct.

    According to the Bently manual, the front impact sensors are located inside the MRS control module, which is on the hump, under the center console, just ahead of the shifter.

    Apparently all that is needed to activate the sensors is a good whack on the center hump (no frontal impact required).

    vc

  4. #4
    Robert Platt Bell
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    accelerometers


    I'm willing to bet the modern crash sensors use solid state accelerometers (accelerometer on a chip) which has a micro-machined pendulum made of silicon. Sometimes they use what is called a 'rebalance' accelerometer, where force is applied to the beam to keep it in place and the force measured to keep it there is a function of acceleration.

    The days of bumper-mounted plunger sensors are long gone.

    A sudden shock load like a kick in the hump by a flying driveshaft could generate 100g's of instantaneous acceleration, more than enough to set it off.

    Sort of a freak occurrence, I'd think. Although this illustrates why disconnecting the battery is a good idea if you are working near an airbag.

  5. #5
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    Thanks Robert!!!

    You're always very insightful when it comes to electronics. I like it cuz you always teach me something new!!! Thanks
    ---------------------------------



    1998 Z3 1.9 - few modifications here and there
    1999 Z3 2.8 - individual edition (British Traditional)
    2003 Z4 2.5i


  6. #6
    Robert Platt Bell
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    Instrumentation Technician

    I studied automotive engineering at General Motors Institute. Before I got my EE degree, I was an instrumentation technician at United Technologies. At the Patent Office, I examined accelerometer applications.

    Solid state accelerometers and gyros (three accelerometers basically) are very common these days in inertial navigation systems, shock sensing, etc. (I am sure that is what they use in those Lenovo thinkpads that sense being dropped and shut down the hard drive before impact).

    Very few companies use large mechanical sensors anymore, when these semiconductor devices can be made, and integrated into a control circuit, for fractions of a penny. The days of the mechanical gyroscope are numbered.

    This Bosch sensor from 1989 (see link) uses a pendulous accelerometer in a viscous fluid to detect rollover. I think it was used in the Mercedes SL with the early retractable rollbars.

    But I think since those days, most manufacturers have switched to solid state devices.

    While a driveshaft whacking the transmission hump might not seem like enough force to set off an airbag, in terms of instantaneous acceleration, it could be well over 100gs or so. Sudden shocks can have very high acceleration spikes like that.

    FWIW.

  7. #7
    CodyR
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    Wow! Is he ok?

    I would think that the guibo breaking would be a shock in itself - then to have both airbags deploy! Seems like maintaining control might be a challenge. I hope everything is ok.
    Aren't the airbags expensive to replace? Will he file an insurance claim?

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    He's fine.

    He has just one small cut on his arm from airbag debris. He was able to safely coast to the side of the road. I don't know how he was able to do that with an airbag in his face (he had to manually deflate it to see out the windshield, which was shattered). That passenger airbag destroyed the passenger side of the car. The dash is split in half, the glove box is hanging out, all of the A/C ducts are blown out, the rearview mirror was destroyed, the sunvisor is broken, and the windshield is shattered and bulged out about 2 inches.

    The insurance company is going to look at it today. I don't know if they will cover it or not.

    The guibo breakage and the airbag deployment were simultaneous. He just heard a boom, then couldn't see anything. The car was completely filled with white smoke and inflated airbags.

    vc

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    Where did you buy the guibo?

    I could take a guess, but...
    ---------------------------------



    1998 Z3 1.9 - few modifications here and there
    1999 Z3 2.8 - individual edition (British Traditional)
    2003 Z4 2.5i


  10. #10
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    Your guess would probably be correct.

    I'll need to double check my purchase records, but my memory supports your likely guess.

    vc

  11. #11
    CodyR
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    Fill me in so I don't make that mistake ;-)


  12. #12
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    Those bastards!!!!

    I was looking around for a guibo some time ago for the 2.8 and noticed that the suspect was quoting something like 50% BMW MSRP or some crazy discount like that... Since I've bought some exhaust hanger from them in the past that failed after some 1500 miles I decided not to buy it form them... And your experience is making me happy I didn't...

    I'm wondering if they could be liable for something like what happened to you?

    But PLEASE, post their name, if indeed is them: people gotta know!!!!
    ---------------------------------



    1998 Z3 1.9 - few modifications here and there
    1999 Z3 2.8 - individual edition (British Traditional)
    2003 Z4 2.5i


  13. #13
    Z3AtlBlu
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    Re: Your guess would probably be correct.

    Yes. Please let us know. I am going to replace mine soon.

  14. #14
    ZGator
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    Re: Where did you buy the guibo?

    Wow,
    I was about to replace my guibo/flex joint for maintenance at 94k, but now I am wondering if that was a good thing or bad thing??

    Please do tell where it was purchased if defective..

  15. #15
    TexZan (Dover, DE)
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    I got mine at BMW, no problems...

    ...and huskerbmw has GREAT discounts on BMW parts if you're a BMWCCA member. I'd take a look at them.

  16. #16
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    Re: Unusual front airbag deployment.


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    Looking at that picture reminds you why

    you don't use cut-rate windshield replacement outfits. That totaly sucks....

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  18. #18
    CodyR
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    Man, that's terrible!!

    I'm wondering if the insurance company may try to total it...
    If so, it would be a good one to buy back from them ;-)

  19. #19
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    Yes | No

    Any updates?


    ---------------------------------



    1998 Z3 1.9 - few modifications here and there
    1999 Z3 2.8 - individual edition (British Traditional)
    2003 Z4 2.5i


  20. #20
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    Yes | No

    Not yet.

    I'm still out of town and will not return until Tuesday.

    vc

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