[urq] Shaking in the rain - 87 5ktq

[Dave C]

I just returned from a trip to Florida and Georgia in the 87 5ktq
where the monsoon season was in full swing.  A problem developed
during hi-speed driving on roads with accumulated water ... the car
would develop a violent shudder like an out of balance washing
machine.  It seemed to be coming from under the middle of the car.
Taking my foot off the accelerator or shifting in to neutral made no
difference.  Slowing down would cause the shuddering to slow down.
I'd coast to a stop, wait briefly, then go on and all would be normal
until I'd pass through more water and this would bring it on again.
Brief water wouldn't do it .... many minutes of high speed water on
the road would
bring it on.  Wet roads, spray, and normal rain were no problem,
torrential downpours with inch deep water on the road would bring it
on.

It kind of felt like the center drive shaft was out of balance or
alignment.  I looked at the driveshaft, carrier bearing, etc and all
appear normal.  But what do I know?  There are 140k miles on the car
and as far as I know there has never been any work done on the
driveshaft, carrier bearing, etc.  The center U-jouint was greased the
U-joint within the past month.

Any ideas?
- -
Dave C.