A friend of mine has a 1995 Geo Tracker 1.6 liter, 8 valve, with manual transmission. Recently this vehicle has started popping out of 4WD, back into 2WD. This is happening at speed, anywhere between 20 and 40 mph. Straight line driving down the road. The transfer case shifter feels and operates as normal. This Tracker is about as stock as they come. Mileage is about 125,000 miles. Any help here would be appreciated. I told her that somebody here would probably have an answer for this problem.

   Sincerely,
   Nine Pine 

Could be 1 of 2 things ... (that I can think of immediately)

There are a couple of bolts that control the pressure of the detent balls that hold the shifter in place. It might be one of those has loosened. They are on the top of the tcase and can be accessed by pulling the tcase shifter boot ...

It also could be that a motor mount is wornout and causing the drivetrain to flex more under torque. If that happens, the tcase shifter could be hitting the tunnel and knocking it outta 4wd.

or the shifter boot is bunched up causing this, or the metal plate that holds the shifter boot in place needs to be flipped around so its not so close to the shifter.

That was the cause of mine....