So I decided that after 240k miles I needed to replace my front U-joints in the front hubs. So I jacked the truck up, put it on a jack stand, took off the tire the brake caliper the rotor and the hub. After I got all this off I grabbed the front axle shaft and there is a ton of slop in it. I can grab the shaft and it will actually move up and down about half an inch either way. It's also not just the axle shaft but after the u-joint the shaft going into the differential has slop in it too. It will move up and down also. What is the problem here and what do I do about it? The truck runs fine until 4wd is engaged.

 

pull the wheel bearing out and check the inside bearing that the axle rides in if bad replace it, should just drive out. 2nd make sure the 4x4 hub hasn't got any slack on the inside where the axle end rides into. 3rd replace axle u joints if has slack in joints and last replace the big hub seals on the axles. You can take just the axles into a ford dealer if you don't have the special driver to install them on the axles. They shouldn't charge much to just replace the axle hub seals. make sure all wheel bearing O-rings are ok, if not replace them. Also on your axle end make sure the part that rides on the wheel bearing inner bearing hasn't got chewed up if it has may have to replace the axle end.