Inspecting your driveshafts frequently is a good idea, especially if you play in the rocks, mud, or water. You want to put the parking brake on and put your Jeep in Neutral. Now climb under there and start twisting. You want to feel for any give, slop, or looseness. Replace any U-joints that exhibit any of these symptoms. Also, look for dents in the driveshaft tubing, missing weights, and these little tangs on the yokes. If these are broken the U-joint is probably off center in the yoke and your driveshaft is gonna poop out sooner rather than later.