The rules for checking the pinion bearings on a rear axle also apply to a front axle, along with some potential problems for the steering knuckles. Check that there is a thin coating of grease covering the knuckle balls from top to bottom. Accumulations of crud on the knuckle balls can indicate one of two things. Grease indicates that the knuckle seals/wipers are shot. Gear oil indicates that the seal inside the axle tube. Either problem requires complete disassembly of the knuckles. If the balls are dry, they've been run improperly lubricated for quite a while and at least the upper knuckle bearings will be destroyed. If the tire can be grabbed by the top and rocked back and forth, either the wheel bearing is loose, or the knuckle bearings are shot. Get someone else to try and rock the wheel and watch if it's moving relative to the knuckle or if the knuckle is moving relative to the axle tube. Quite often if the wheel bearings are loose, they are simply in need of re-packing and adjustment.
On a loose surface (not pavement) lock the hubs and put the transfer case into 4WD. Then drive slowly in a circle to the left and to the right. If a rhythmic clicking noise comes from the front end, the Birfields are worn and need replacement.