hillbilleous

i just recently picked up a 2003 trailblazer with the 4.2l 6cyl. and the 4 wheel drive doesn't work. I do know the transfer case is working and shifting into gear and I also know the front axle actuator is working. The problem I have is the shift fork in the front differential doesn't seem to move far enough to lock the front axles. The front diff. also looks very scary to remove and pull apart being how it is part of the oil pan (looks like one big chunk of aluminium). Anyone have any info. or input that could solve my demise?