2000 4wd blazer, 4wd not engaging. did the homemade posilock but still no 4wd. 3 position button works and seems to shift tcase. i can hear clicking from the tcase and 4lo gears engage but no power to front. what would cause the front drive shaft to not turn in 4wd, or could the shifting mechanism in the front diff be messed up. no grinding noises or pops or cluncks. any ideas? im new, so go slow.