99 Dodge Grand Caravan AWD drive train problem

Hello all. I just purchased a 99 Dodge Grand Caravan AWD with 79K,
from the original owner. The car has been well maintained with all
receipts, except for probably the most important maintenance, the
transmission. I had originally thought the transmission had been
flushed at 46K because there was a BG sticker under the hood. After
reviewing the receipts I determined it was a BG brake line flush
during some brake work. Anyway I have noticed that at between 45-55
MPH when I am applying the accelerator (even lightly) that there is a
washboard like sound and vibration. It almost seems to come from the
back of the vehicle but definitely sounds like the drive train. If I
let off the gas the sounds disappears. The sound/vibration also seems
to appear during low speed acceleration when I am turning the vehicle
(though it is not nearly as pronounced). If I drive in 3 instead of D
(3rd instead 4th) the sound does not appear when doing 45-55. I am
leaning towards the transmission, but wonder if it could be the all
wheel drive system. I have purchased a new Chrysler filter, 10 quarts
of ATF+3, and plan on dropping the pan this evening. I will then
disconnect the cooler line from the trans and try to flush out as much
of the old fluid as possible. Anyway, does this sound like a
transmission problem? The car does not slip and shifts pretty
smoothly.

Thanks,

 

Dropped the pan replaced the filter and let the trans drain for a few
hours. Replaced with 6 quarts of ATF+3. Ran the car for 5 minutes or
so. going through the gears. Dropped pan again and drained. Replaced
with another 5 quarts of ATF+3. Still have the shudder. I swear the
sound seems to come from the rear of the vehicle. But it does not
happen if I am in third gear at the same speed. Only happens in 4th.

Lonnie

 

4th gear only would seem to indict the Torque Converter....

 

I had a similar problem, a noise and vibration under light throttle while in
high gear. It was a few years ago while my '97 was still under warranty so
I don't remember every detail. I could hear and feel it from the driver's
seat, but it was not too bad. It was much worse sitting in the midcabin
seats. The AWD cars have two shafts supported by a bearing. The shaft, I
think the forward one and the bearing were bad. They were replaced under
warranty. If you are not under warranty I would live with it or be prepared
to part with your wallet.