This is my 4th GM 4x4 ('99 1500 silverado, w autotrac) My old '98 and my '04 dmax do not have autotrac, but my wifes '04 trailblazer does have it. Every vehicle except this '99 you can crawel under and manually spin the front drive shaft when the vehicles are in 2x4, the '99 will not spin. It is not stuck in 4x4 (I can easliy tell by driving), and when I push 4x4 hi or auto 4x4 it is audible going into 4x4. Is this normal? I would think that if the front drive shaft does not spin freely, then that means the transfer case is in 4x4, and hence the front axles would spin? That can't be good! I found this condition while trying to locate the source of the drive train noise I get while in 4x4. Rear u joints were replaced, and the front u joints seem ok. Only play in the system is the front yoke out of the rear of the transfer case has some play when you push it up and down (I read this was normal--hence the "clunk" you get dropping it into gear).

Yes its normal for the front shaft to be engaged, part of how the auto 4x4 works.

Yeah the autotrac transfer case clutches are holding the driveline. The first time I changed the oil on my 2000 I was worried too when I couldn't turn the driveline... But I found out is was ok because the autotrac holds it. You might notice under the hood a sticker that says to only run it on a 4 wheel dyno too...

Yea saw that sticker. Guess the auto 4x4 in the trailblazer is different.