Any chance somebody can lay it all out for all of us novice's? Maybe pictures or just a step by step?
There are two driveshafts ("propeller shafts" in the service manual) on a 4WD FJC, front and rear. Each of the two driveshafts has two universal joints, one on each end of the driveshaft. The grease zerks are right in the middle of the u-joint spider, and are angled so that you can get a grease gun fitting on them - but because they are angled, the u-joint must be rotated in the right direction so that the zerk is accessible. This is done by turning the driveshaft.
Crawl under the truck with your grease gun and a good work light. A grease gun with a flexible hose rather than a rigid tube is easier to use for this purpose. Using the light, find the zerk and see which way it is pointing. The best place for the zerk to point (IMO) is about horizontal, towards the passenger side of the truck. If you're lucky and the zerk is already pointed that way, push the nozzle end of the grease gun firmly on the zerk as straight as possible until you feel it engage the zerk, and pump until you see grease start to weep out of the dust covers/seals of the needle bearings in the u-joint. If the zerk is not pointing the right way, you'll have to turn the driveshaft (and the u-joints with it) until it is. On the front driveshaft of an auto tranny FJC, you can turn it with your hand while you're under there. For this reason, do the front driveshaft first if you have an auto tranny. For the rear driveshaft of an AT5 truck and both driveshafts of an MT6, you'll have to get out from under the truck, put it in neutral, and roll it forward or back about 6" and try again (don't forget to put it back in gear or "park" and set the parking brake before you get back under the truck). You may have to do this more than once to get the optimal position. the zerks in both u-joints point the same way, so if one has assumed the (right) position
then the other will have too.
Each driveshaft also has one slip yoke each, located on the transmission end or transfer case end of a given drive shaft. The slip yoke is just a splined shaft within a matching-splined tube, that allows extension and contraction of the length of the driveshaft while maintaining torsional rigidity (the driveshaft always turns, no matter if it is extended or contracted). There is one grease zerk on each slip yoke. The zerk is easy to find, as it on the outside of the u-joint. Because it is on the outside, it is much easier to get to and more forgiving of the angle needed to get the grease gun nozzle on it. If the zerks inside the u-joints are aligned, then the slip yoke zerk will be too. DO NOT grease the slip yokes until grease comes out between the shaft and the tube, or you risk hydraulically locking the slip yoke which would not allow any contraction and can be hard on the bearings and seals. Three or four pumps of the grease gun is plenty - it's not a bearing surface, it just needs a little lube.
When you're all done, you should have greased four u-joints and two slip yokes for six zerks total. The service manual also says to check the torque on the u-joint flange bolts while you're down there greasing, but mine have never been loose yet. The torque spec is 65 ft.lbs.