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High Speed Engine Vibration With New Mounts (M30)

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    High Speed Engine Vibration With New Mounts (M30)

    I noticed after some time on the stock M20 mounts that my M30 had compressed and stretched out my passenger side mount. The motor was sitting on my steering rack a bit, oil pan is fine and pretty sure the rack is fine too...

    Exactly the same situation as this thread: http://www.r3vlimited.com/board/showthread.php?t=398836
    From the recommendations there I replaced the mounts with new revshift 80A polys for the M20.

    I also used some thick washers in there to make sure the engine wouldn't sit on my steering rack again. I raised it maybe .5 to 1cm

    It seems to sit there just fine, but immediately after installing the new mounts I noticed some vibrations coming from the engine bay. From the driver's perspective, the shaking is right in the middle of the firewall, basically where the radio is. It only happens at freeway speeds (60-70mph, haven't gone faster recently for this reason) and when the engine is under load.

    The vibration was not present before I changed the mounts. My driveshaft U-Joints were fine last I checked and the two shaft halves were aligned properly before reinstall (way back when I swapped my 2.93 open for an LSD and noticed my old driveshaft joints were stuck), giubo and CSB have probably 1000 miles on them at most.

    Is it possible that I used too many washers and that my engine sits too high now? Would that alone cause vibration? I double checked my firewall clearance and I couldn't see or feel anything making contact. Or is this just my life now with poly mounts? It gets bad enough that my radio starts sliding out of its housing (yeah, yeah, I need to secure it...).

    Thanks as always.

    #2
    Urethane bushings, even 80A hardness, are going to be firmer than the OEM rubber bushings. So some increase in NVH (noise, vibration, and harshness) is to be expected. That being said, I have some 80A mounts made by a R3v member and there is little to no NVH that I can feel. I would double check that the engine isn't touching anything like the oil pan, steering rack, transmission tunnel, firewall, etc.

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      #3
      it's going to be vibraty as shit with anything through bolt.
      Doesn't matter what the mount material is.

      you're probably rubbing on something but if you want a nice non race-only mount
      get the ie ones. very nice. i like.

      btw my oil pan i think actually touches the steering rack that's not making it vibrating.

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        #4
        Hmm. Alright, thanks for the feedback. I'll take a look and see if anything else might be hitting the body, maybe the transmission? There's a few things that need fixing on the car before I take it out again but next time I do I'll try and get some video of it or something, and you can tell me if I'm just being a baby and not to worry.

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          #5
          I'm a little embarrassed but just in case someone somehow gets this problem, I discovered the other day the engine was hitting the hood when closed... :curse:
          I over-corrected I guess, but still preferable to hitting my steering rack. All it took was taking off the AFM's plastic cover and it's fine now.

          Now I'm just curious why my engine shakes so darn much. It sounds a little misfire-y, though not severely, seems down on power, and runs crazy rich right now. Am I missing a cylinder perhaps? But anyway, that's another problem...

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