I've made reference to this method for removing u-joints on here many times over the years since I originally read Big_Mark's post 14 years 
ago. He added some photos to illustrate it that are now gone and I thought it was worth reposting with video.
Here's the original thread where he posted it (not a lot of use without pics to explain, but as credit where it's due):
https://www.cj-8.com/threads/article-u-joint-replacement-procedure-go-to-thread-for-pics.6744/
Here's a non-Jeep video I found that shows how to do it. I have been able to remove every joint/cap in minutes, even some where other folks had failed with pressing them out using the sockets/vice "press" method and were ready to give up.
The key part starts at 1:51, where he shows which part of the shaft to hit while resting the ears of the other side of the shaft or the ends of the u-joint cross on the vice. You're hitting down on the shaft/ear (start really easy--I think he hits it too hard to start) to pop out the top cap. The video shows it really well other than he goes at it pretty hard straight off.
Here are my comments to supplement this:
-You can use rocks/wood/etc to support the ears on other side of the shaft or u-joint cross (be careful and sensible), so this is great for trail repairs. Just be sure the ear on the underside of the shaft you're hitting is hanging in space and not resting on anything.
-IT OFTEN DOESN'T TAKE MUCH FORCE - START EASY, there's no reason to beat the hell out of the shaft if it's not needed, a bigger hammer and less force is ideal IMO. The impact load makes all the difference in this method over pressing them out slowly, so use that to your advantage and only use the force needed. Once the cap moves even a fraction, it usually pops out from there very easily.
-If you have to reuse the u-joint for some reason, this may not be the way to go for the second set of caps because you have to rest the u-joint cross on the vise/blocks (2:03 in the video). If the caps pop out easily, you won't do much visible damage to the bearing surfaces of the cross, but I'd consider it an emergency-only way to go. I'd probably try supporting the shaft on something and then putting a socket on the top cap to hit to drive out the bottom cap. (You can use this for all the caps, but I don't think it works as well/easily if you don't need to worry about reusing the joint.) This video shows the hammer and socket version at 1:33 -
-Watch the needle bearings carefully if you have to reuse the joint--if there's not much lube in the cross, they could scatter when the cap pops up or when you remove the cap from the shaft ear. Doing this over a clean towel or tarp is a good idea (a shirt works in a pinch).
-If using a vice, I try to put a towel on the vice under the shaft just in case it slips through
-Once the new joint is installed, you can use this method LIGHTLY to "seat" the caps back in the ears. (He sort of does this at 13:06, but you can see his tapping doesn't really free the u-joint up enough.) When all clips are in place, you can tap the shafts to push the caps back into the ears so that the cross isn't bound up at all to allow the joint to move as smoothly as possible.
Sometimes you can manage to get the clips in but the cap is pushed against the end of the cross tightly enough to cause interference, so the joint won't feel "smooth" (as you can see in the video around 13:06.) Putting all the ears of the finished shaft back in the vice with a couple VERY, VERY LIGHT taps on all ears will push the caps back and free it up. Even if the joint feels smooth, I like that doing this seats the caps against the clips as well as possible to help ensure the clips stay in place.
Hope this helps folks. I have thanked Big_Mark in my head dozens of times over the years for making me aware of this method and owe him many, many beers in gratitude (he sold his Scrambler and hasn't been on in years.)
