Member, Sport: Off DSC: On (>50 posts)
Join Date: Oct 2008
Location: Orange County
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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.
2012 S197 Mustang GT Premium, Performance White
2003 E39 M5, Carbon Black Metallic
2007 E90 335i, 6MT, Sparkling Graphite Metallic
2002 E46 325i, 5MT, Topaz Blue Metallic