ok here we go
170000 miles on a 6 speed
recently changed both driveshafts, a week later I'm on my way to work, cruising at 45mph.. my tach redlined, I'm thinking it popped outta gear. Nope, it's in gear, just no gears are engaged. Towed her home thinking tranny was mush, jacked her up and spun the wheels everything seemed good, no crunchy sounds or binding. Put her on the ground and voila, gears... took her for a spin and all was good. Next day decide to do another test,2 miles from home, again no gears ... no pending sounds of doom, clutch is not slipping and has full range of movement..
now you can hear movement in the case when it's in gear, nothing bad just a quiet whirrr....

so so all this is quite bewildering, what the heck is going on here?? Could the new driveshafts have something to do with this?? Damage to the diff??? I have to pull the engine and split the trannie off to find the issue I'm sure, but was hoping someone had any idea what this could possibly be...

again no clonks, grinding or banging going on, just no power to the wheels

 

When installing the driveshafts, if you failed to ensure the driver side is fully pushed in so the circlip is engage, it can damage the splines as they have insufficient engagement. I think it happen to someone here. In his case the damage was at the end of the spline shaft so once he realize it, he got it to work. I was so worry I immediately went and checked mine, but mine installed by untrained Maestro mechanic, is all good.

 

Moving you to the Stock Problems/Issues area.

Suggest you jack the car up and see how close the axles are to the transfer case. I am thinking there should be no more than a 1/4" gap.

 

Given your symptom, there are only a few possibilities that make sense. Drive axle not fully seated. Shift linkage problem. Clutch not engaging.