Berlina driveshaft vibration

["Watry, Andrew (LNG-SFR)" <Andrew.Watry@domain.elided>]

I know it's a time-honored topic, but I wonder if anyone has had this
specific apparent driveshaft vibration problem.  My 2000 Berlina has a
rumble/vibration in the driveline only in one circumstance: at relatively
high speed, like above 50 MPH on the freeway, and only when the gas is
feathered so that the car is neither accelerating nor decelerating, but just
holding steady with the lightest throttle.  Getting back on the gas, or
letting the car coast fully against the gears, makes the rumble disappear.
I have the rear driveshaft piece out and at least one U-joint is bad, so
I'll start there.  I know there are other steps to go through, including
checking that the trans and pinion yokes are not loose, and have also heard
that pinion shaft can be running fore and aft in the diff. casing, creating
this kind of situation.  But I wonder if anyone has experienced and solved
this specific problem without going through the full, expensive range of
driveshaft remedies.  Donut is new, carrier bearing and rubber seem good,
trans mount is good, ball on output shaft and front bushing seem good, etc.
Thanks for any experiences.

Andrew Watry
Berlina Register
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