Anyone solve the 3k Vibration? - Page 27 - BMW M5 Forum and M6 Forums

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Old 3rd November 2009, 01:08   #261
nightkrawler
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Originally Posted by vantaam5 View Post
One of us has to find it out,I think!
BTW,the problem I pmed you about I solved(DIS)!

Have the car tomorrow on a four stamp lift and try to locate the way of the vibrations!
yes, we have to figure this out as it is driving me crazy. get in the car and have your helper raise you up on the lift. get the rpms up where you feel the vibration and then have your helper pry on the exhaust, motor mounting, tranny etc and see if it has any change on the vibration. i dont understand why when we jack up the front end it goes away, this dosent make any sense. what is changing when the front wheels are off the ground?
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Old 3rd November 2009, 09:57   #262
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Quote:
Originally Posted by nightkrawler View Post
yes, we have to figure this out as it is driving me crazy. get in the car and have your helper raise you up on the lift. get the rpms up where you feel the vibration and then have your helper pry on the exhaust, motor mounting, tranny etc and see if it has any change on the vibration. i dont understand why when we jack up the front end it goes away, this dosent make any sense. what is changing when the front wheels are off the ground?
I think I posted somewhere earlier in this thread a wild theory on that the wheels in the air could act as vibration dampers
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Old 3rd November 2009, 10:24   #263
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Quote:
Originally Posted by nightkrawler View Post
yes, we have to figure this out as it is driving me crazy. get in the car and have your helper raise you up on the lift. get the rpms up where you feel the vibration and then have your helper pry on the exhaust, motor mounting, tranny etc and see if it has any change on the vibration. i dont understand why when we jack up the front end it goes away, this dosent make any sense. what is changing when the front wheels are off the ground?
The only explanation I have that it is submitted through the subframe and suspension parts in front...
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Old 3rd November 2009, 13:09   #264
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iirc when i was using the vibration analyzer i took readings from the subframe and i got none.
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Old 3rd November 2009, 21:54   #265
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Could not detect vibrations on subframe!Coulöd detect vibrations from the gearboxmount to the body
But change 2k ago tranny mounts...
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Old 4th November 2009, 02:24   #266
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Originally Posted by vantaam5 View Post
Could not detect vibrations on subframe!Coulöd detect vibrations from the gearboxmount to the body
But change 2k ago tranny mounts...
explain better please, how did you "detect" the vibration? i guess everyone else has given up so i guess its up to us to figure this out.

when i was using the vibration analyzer i also picked up vibrations on the tranny crossmember. idk how they are being transmitted through the rubber mounts to the body. if this is definitely the route the vibration is being transferred from then prehaps we need a different type of mount. prehaps something custom fabricated.

we may be on to something here. when the front end is jacked up the engine/transmission should be tilting forward slightly. this is probably taking pressure off the tranny mounts hence why the vibration is gone.

Last edited by nightkrawler; 4th November 2009 at 02:24.
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Old 4th November 2009, 12:12   #267
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Due to no fancy measuring stuff around,I used a screwdriver and felt them in my hands because they were so pronounced!
Would be intersting to know if it is different with the Rogue mounts!
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Old 4th November 2009, 13:23   #268
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Due to no fancy measuring stuff around,I used a screwdriver and felt them in my hands because they were so pronounced!
Would be intersting to know if it is different with the Rogue mounts!
i believe we are getting close here, i dont know why i didnt pursue this route a long time ago. now the question is what is the problem with the factory mounts? are they too soft or too hard? i would assume that the harder the mount material, the more vibration it is going to transfer. ie a solid aluminum mount would probably be 10x worse.

so what do we do... prehaps try various mounts from different cars? there are many other bmws that use the same style transmission mount. so im thinking here what car would bmw engineer where any sort of vibration would be unacceptable...? E65 7 series maybe? the E65 mounts look to be the same design as the M5 mounts, im going to get a set for the hell of it as they are pretty cheap. im also going to call uuc/rouge and ask them about various mounts. here is the e65 mount.
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Old 4th November 2009, 14:55   #269
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This is a great idea,nightcrawler!
For checking if too stiff,I try to getan aluminium block,drill a hole through it and mount it stiff to the tranny/mount!
Will do tomorrow and keep you updated!
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Old 4th November 2009, 20:53   #270
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Could the mounts be overtorqued? I know that when I bought UUC mounts for my E46, the instructions were very particular about the torque specs. I think it was something like 14 ft-lbs, or just slightly tighter than finger tight. When I installed them, I overtorqued them (and not by much!) and there were vibrations all throughout the rev range. I can't imagine the factory mounts are much different WRT torque specs, though I don't have a bentley on hand so I can't confirm.

Also, the tranny can't be preloaded when the mounts are tightened. The car needs to be level, started and revved while the mounts are loose, then tightened to spec.

Lastly, the black UUC mounts, which are the softest ones they have available, were much much stiffer than stock. Even when properly torqued, there was a (minor) increase in vibration. I doubt that stiffer mounts will make the vibrations go away, but using softer mounts from "softer" cars like the E65 sounds promising.
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