With thanks to AlfaGTV6.com
Driveshaft:
Bad centering bearings. There are three.
Bad center support (or bearing)
Bad donut
Bent driveshaft
Bad driveshaft (poorly made)
Overcentering of the center or rear bearing
Missing bushing in the donut (rear only)
Too much grease (clogged vent hole)
Bent front flange.
Worn front flange.
Improper hardware (mismatched bolts, washers, nuts)
Center yoke improperly aligned after center support changed
Bent nose or tail area
Missing weight (or 'extra' weight)
Improperly installed donuts
Misaligned driveshaft (generally has to do with engine or transmission)
Engine:
Engine mounts 'stressed' in some fashion
Flywheel missing bushing for the front alignment bushing
Bent bolts on the flywheel
Engine twisted on its mounts
Transmission:
Bad rear mount
Bad front mount
Stressed front mount(s)
Transaxle mounts installed improperly (cut off bottom plate on GTV6)
Bad clutch (out of balance)
Improperly adjusted 'pinion' stop (gap should be ~1/8", use drill bits to measure, roll them in.
Warped clutch housing
HA HA where to start
take your pick.
very good info there
Wow, that's quite the list.
I had a donut fly off recently (scared the pants off me, after the rubber piece flew off at ~5000rpm and bounced off the road right back up on the floor, huge noise - throught the prop shaft had fallen off or something), when the new donut was installed it was a few mil too big and knocked against the handbrake cable under load. Weird.
Thanks for the list, might come in handy one day.