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      06-17-2022, 03:27 AM   #320
BimmerPost Supporting Vendor
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Drives: E92 M3
Join Date: Feb 2014
Location: San Dimas, CA

iTrader: (2)

Resonance vs Vibrations

Hey guys. Just wanted to explain some vibrational "issues" that may occur after installing the driveshaft.

Resonance is actually related to vibration (it's the result of vibration), however, the vibrations you get can be split into two variations:

1) Balance vibrations - This is what a few of you experienced before (thus their car shaking) and was due to the balancing of the tube. This is what we set out to resolve and have now resolved

2) Harmonic vibrations - This isn't related to the balancing of the tube, but your chassis components/setup. As the driveshaft is basically a hollow carbon tube that does not absorb any harmonic vibrations whatsoever (the only parts of the driveshaft that could absorb anything would be the aluminium flanges/CV), this job is basically left up to your chassis bushings (guibo, diff, subframe, transmission, engine etc).

To simplify it, harmonic vibrations can be split into 3 stages:

1) Minimal - Your chassis components are virtually "as new" and do their job in absorbing everything

2) Medium - Your chassis components are starting to show their age thus do not completely absorb everything. This translates into audible resonance like what you may be experiencing. If you have upgraded to harder/solid bushings or mounts, these also do not absorb as much of the vibrations

3) Advanced - Your chassis components need replacing. Not only will you get audible resonance, but actual physical vibrations may be felt as well. The further along the degradation, the more pronounced the audible and/or physical vibrations will be. This is what occured with our previous MT tester, hence it delaying us assembling more pieces due to wanting to diagnose and resolve the issue. After he replaced his transmission mounts and guibo, the issues were resolved. Unfortunately, once you reach this stage, it is a matter of trial & error to pin point which components are shot

Both v1 and v2 had the same harmonic issues as it wasn't really anything to do with the balancing or design of the driveshaft. The sound during coasting/wind-down is due to the hollow nature of the tube (it may actually sound "louder" than during throttle). If you are already experiencing any vibrations in-cabin (non driveshaft related), I'm sure you will notice that vibrations almost always get worse when you lift-off the throttle versus keeping your foot down. This is the same principle.

As always, if you have any questions, please do not hesitate to contact me
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