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unknown vibration

This is a discussion on unknown vibration within the Internal Engine forums, part of the LSx Technical Help Section category; i'm having a pulsing vibration starting around 2100 rpm,have no idea what this could be,my car runs great,like a beast,but ...

  1. #1
    Junior Member JROBINSON1016's Avatar
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    RED
    1998 TRANS AM

    unknown vibration

    i'm having a pulsing vibration starting around 2100 rpm,have no idea what this could be,my car runs great,like a beast,but the vibration is really bad.
    doesn't seem to affect performance,i've checked mounts,motor & transmission. i can rev it in neutral or park,like i said it starts just above 2k rpm. it isn't a constant steady vibration,it seems to pulse,like some kind of cycle. does anyone have any ideas,this is driving me kra-z.

  2. #2
    Member 346ci's Avatar
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    NBM
    1998 Z-28

    I have this too and have been trying to figure it out for a couple months now, although I don't think it's an internal engine problem

  3. #3
    Junior Member JROBINSON1016's Avatar
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    RED
    1998 TRANS AM

    i don't think it's transmission,i've had mine changed,vibration's still there,has to be something with the motor,i checked my injectors,unplugged one at a time,so that's not it,also checked mounts as i already mentioned. anyone have any ideas?

  4. #4
    Junior Member sjones69's Avatar
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    RED
    1998 Trans Am, A4

    I had a vibration last spring. I replaced the transmission mount (summit prothane) back to a stock one (rubber) and replaced the stall. Took care of my problem.

    Good luck.

  5. #5
    Junior Member JROBINSON1016's Avatar
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    RED
    1998 TRANS AM

    tell me more about the problem you had with your stall convertor,my trans mount is good,no problem there

  6. #6
    Junior Member sjones69's Avatar
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    RED
    1998 Trans Am, A4

    Quote Originally Posted by JROBINSON1016 View Post
    tell me more about the problem you had with your stall convertor,my trans mount is good,no problem there
    I had the tranny rebuilt. Shift kit, new stall, mount. Drove it home and noticed a vibration. didn't noticed it as bad on higher RPM's, really bad around 2000. Driving it down the road at a steady RPM it would vibrate on & off (vibrate 2 seconds, off 2 seconds). Brought it back and the tranny guy replaced the stall, he said it still had a small vibration (I wasn't there to feel it), so he also replaced the prothane mount. I have heard the prothane mounts will transfer some vibration to the frame.
    Once I got it back I haven't had any problems. So mine seemed to be a bad stall, and the tranny mount.
    Hope this helps find your problem.

  7. #7
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    1999 Z28

    I went through this last spring and had the mechanic do the following in order to find it...I had all the tires /wheels balanced - driveshaft balanced - tranny mount inspected - new u joints - brake rotors checked out etc etc and they could find the source of the vibration and they thought perhaps it was the internals of the engine...
    For a chance at narrowing it down while they still had the driveshaft out and the car was on the lift they put the car in drive and gave it some gas and found that the vibration was coming from the tranny, the tranny mount that was put in just before it was parked for the winter was not doing its job in supporting the tranny. It was a brand name unit that was used but I can not remember which one....never the less they put back in a stock tranny mount rather than the polyblabla one and the car ran without the violent shakes any longer and was as good as new. I never would have guessed that a "new" tranny mount would have been the culprit but it was....worth looking into.

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