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    HELP! My Boxster shakes, but why??

    Experiencing a strange shaking in my 986 (2003/70.000km) at certain speeds.
    I previously wrote about my Falken winter tires that caused rattling in the rear suspension at around 130 kph, but now that I have changed to 18" carrera S summer rims and SP9000 rubber, I thought it would go away. The shaking is still there albeit in a different manner.

    When I take the cold car out in the morning, it always feels like Im driving on rippled asphalt the first 1-2 km. Then it gradually fades.
    But when the car is warm and I take it to the freeway it begins shaking mildly or vibrating from the rear at recurring intervals.
    Example: going 130 kph. A mild but noticable shaking appears from the rear. It fades in and fades out again after 2 seconds. It's gone for 2 seconds then it comes back the same way.
    Like in a rythm pattern.
    The speed of the vibration changes if I go slower or faster.

    Feels like vibrations in the chassis or from the engine, and I'm beginning to fear that it could be the engine suspension or some such.

    Before taking it to the shop and getting raped I'd like to hear you guys' opinion on this.

    Is it a vibration from the engine?
    Could it be my suspension?
    Anything to do with the wheels/brakes?

    Any help would be appreciated.

    Re: HELP! My Boxster shakes, but why??

    Could be the disc.

    Re: HELP! My Boxster shakes, but why??

    Could be the driver

    Re: HELP! My Boxster shakes, but why??

    just a few guesses/
    1) engine brace problem
    2) wheel aligment?
    3) wheel / centre rings (if they hv any) not fitted properly
    4) damaged suspension from speed hump crashes.

    I had similar prob with my old car.
    it turned out to be the idiots at the tyre store didnt put my aftermarket wheels on my Mini Cooper properly.

    Re: HELP! My Boxster shakes, but why??

    Yeah, I still suspect the wheel alignment/balancing since the new tires were fitted by the same people who fitted my (vibrating) winter tires.

    It's not a really violent vibration, just a damn annoying and disturbing one. Feels like getting an involuntary massage from underneath the car.
    (Perfect lay-up for any sordid massage-jokes...so bringem on! )

    Re: HELP! My Boxster shakes, but why??

    Quote:
    dreamcar said:
    Could be the driver



    I am the prefect driver...in fact, I may be the perfect human being, so that pretty much rules myself out.


    Re: HELP! My Boxster shakes, but why??

    Try wheel balancing as the first item. But take them to a different tire dealer. That would be the cheapest and most likely problem.

    Re: HELP! My Boxster shakes, but why??

    The fact that the vibration fades in and out suggest to me that it is not balancing. These days balancing is all done automatically on a machine, so it is hard for even the thickest work experience boy to get it wrong. The variation in frequency with speed and the fading in and out may point at a resonant frequency being set off at various different speeds. To me this suggests suspension mounting bush wear or any form of rubber bush mounted at the joints in the rear axle/suspension links.

    The onset of vibration fading in and out is caused by two frequencies not quite the same (like two props on an aircraft going at slightly different speeds), so that explains the variation due to speed, but also that the (for example) suspension mounts could be worn different amounts and therfore have different resonant frequencies (same as a glass humming when you rub the rim).

    I'd get it into the garage for a look.

    Hope it isn't serious.

    Re: HELP! My Boxster shakes, but why??

    Thx, JZ.
    Same thoughts I had regarding the out-of-tune vibrating.
    I will be going to the shop, I just wanted to get some qualified input before I go there. Wanna make sure I dont get to pay for a problem that isnt there.

    Re: HELP! My Boxster shakes, but why??

    One item to add to all the other good suggestions is wheel ball bearings, which is harder to feel if the back wheels are the source of the vibration. This problem appeared on my Boxster S once. I tried to isolate the problem first by doing a wheel balancing and checking the tire for irregularities. Nothing fixed. Next a 4-wheel alignment. Problem still there. Then ball bearing. Bingo. Problem solved.

    Re: HELP! My Boxster shakes, but why??

    Steering rack and front end joints.

    or your tires flat spot easy from cold and heat up slow to full round.

    or one tire or more is NOT ROUND !!!!!

    Good luck !!!!

    Re: HELP! My Boxster shakes, but why??

    I had a similar problem on my 986 a while back. It turned out to be a nail that punctured the tire but also sealed it. I drove the car like this for over a month with no air leak. When I left it for the annual service I indicated the slight vibration (it was not always on and nor happened at the same speed).

    They removed the tire and plugged the tire.

     
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