4 Wheel Drive/SUVs: AWD and tires, reputable shop, 4wd vehicle

Question
I purchased a used '94 Aerostar E-AWD. I know this is not even close to an off-road vehicle, but as  i have never owned any AWD/4WD vehicle before any advice will help. The AWD was disconected (unplugged at transfer case)at purchase. After plugging it in everything seemed fine until 15 minutes at highway speed. Vehicle started a pretty severe vibration, almost like hitting grooved pavement. Stopped after 5 seconds. When it stopped it felt sort of like there was a torqueing tension released from the frame. I could actually feel a kick from the right side of my seat. This repeated again after 2 or 3 more miles until I exited expressway and unplugged TC again. The vehicle has mis-matched tires -205/75/14 in front and 195/75/14 in rear. Could this be the cause?  

Answer
Paul,

In any AWD, or 4-Wheel drive, it's extremely important that the tires be a matched set.  If they are not, you will be putting unequal torque on the transfer case.  This can put the transfer case in a bind, and tear up the internal components.  I would suggest that you have the transfer case checked out at a reputable shop, preferably one that specializes in 4-Wheel drives.  I'm not sure why the AWD was disconnected, but in some situations, that can be hard on the TC.

In any case, my suggestion, would be to install a set of matched tires, and keep the AWD hooked up.

Carl