You would think since Yukon makes the 4340's and the Super Joints that they would work flawlessly right out of the package. That is not the case so this post will be dedicated to the installation of Super Joints into the Yukon 4340 chromoly axle. There are several videos on this if you googled it so I won't get into too much detail. What you really need know is, the videos you see make this look like a little/ very minor filing to the axle and its simple. That is not the case. You will need to file the axle very good. I was told Yukon is aware of these issues and filing/grinding will not void the warranty on the axles.
Step one is to file the flanges on the axles very good every surface the joint will contact. While you need to do a lot of filing you want to be careful not to take the hole in the flange out of round or gouge it in places.
Next step is installing the joint into your axle. Once it's in you'll need to put the clips on.
Now the joint is in one axle: grease the caps, grease the O rings you'll install in the caps, and grease the hole in the axle flange.
Now stick the caps on being careful the O ring stays seated. For this you'll need to make sure the joint is pushed out towards your cap as far as possible.
Keeping the cap level, hit the cap down onto the joint. Be sure you strike flush with the hammer. You don't want to damage the threads for the grease zerk, and clip caps to joint (pic below).
Now repeat the process to combine your inner and outer axles.
Clips
Finish by installing grease zerks and greasing joints.
Now that it is all assembled, work the axle to ensure it moves freely on the joints. If it feels stiff give it a few taps with the hammer on the axle flanges and continue to work.