Quote:
Originally Posted by BavarianFanatic
Try depressing the clutch when it occurs to see if there's any change. If there is, it's the driveline - motor, trans or driveshaft. If there isn't, it's the diff, axles, bearings or wheels/tires.
I have a feeling there's an error stacking issue. Components are well within spec individually, but are out of spec as an assembly.
My 335 is buttery smooth. A great number of the components are common to both models.
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Thanks for the advice. No change in Neutral. I understand your comment about tolerance stack - but don't think that's the case here. If that was the case, replacing key components (diff, prop shaft, etc.) should have made a bigger difference than they did. I believe it's a specification issue. If you look underneath, there's a dynamic damper on the rear subframe (43 Hz) and another on the rear diff (80 Hz on MT; 40 Hz on AT). There are labels on the parts that indicate the frequency. I believe these (one or both) are either out of spec from the supplier or tuned incorrectly. These vibration dampers are usually tuned just for this kind of driveline resonance. Unfortunately at the field service level (dealer, BMW NA tech support) there's not much that can be done to troubleshoot other than order new parts and do some trial & error parts swapping. But if the spec if wrong, that won't make much difference.