I replaced engine & Tranny mounts on the SDL recently but still had some vibration felt through the accelerator pedal at certain highway speeds. My mechanic tightened up a locking nut on the driveshaft joint (not exactly sure where) that wasn't loose but could be tightened about half a turn. That eliminated about 40% of the vibration. Replacing both the Rubber Donut flex couplings and the Centre Bearing improved it another 40-50%. The one flex coupling was so hard it was like concrete - no flex at all
Gear changes and overall smoothness are much improved.
I figure the remaining vibration may be down to engine mount shocks that were not replaced with the mounts themselves, or some small binding of the driveshaft universal joint due to operating in a slightly different position after the tranny mount renewal. Could also be related to rear subframe mounts, which are still on my 'to do' list - I'm working my way rearwards
