The cardan is used for both tractor and implement drive lines. Rototiller and spaders are examples of where you will see the cardan joint used.
The two types of cardan joints seen at the left are to a Pasquali tractor with an example of long life sealed u-joints below. If grease type, note the orientation before removal.
To remove the u-joints from the yolks, remove the snap rings and find a suitable size socket that is slightly smaller than one of the u-joint caps. Set the yolk on a hydraulic press with support so that you can press the u-joint downward through the yolk. Once pressed through, remove the free cap, then reverse the procedure for the other.
The Cardan or double u-joint is normally fixed on one side only of the drive train. Look at both sides of the cardan, one end will be fixed with a bolt, grub screw or pin and the other end will be a slip joint. Removing the yolk will never be easy, as you will need to line up the drive line with an opening that will allow you to remove the fixture. Do not be discouraged, removal can be a pain.
Once removed, clean the joint really well. Normally caked with grease and dirt, it pays to clean this piece so it looks new. This will facilitate installing the new u-joints.
Axles are usually removed with a slide hammer or press - but you need to know how they are fixed. Goldoni uses threaded axles and no amount of hammering will pull those through. Older Ferrari's use a heat shrink collar to secure them (500 degrees on the kitchen stove element and some fast handling with channel locks). Stuck bearing races: external - use a press, internal - a one inch bead of weld will loosen them up.
Always refer to the manual when replacing axles. If not available, carefully study the parts diagram where applicable.
Now comes the fun part. Depending on the size of the yolk and design, you will need to remove one or both of the applicable caps to reinstall. Carefully remove a cap, ensuring the rubber seal at the bottom of the cap stays with the cap. This will ensure the bearings will not fall out. Work the joint into the yolk and down, then start the cap on the outside of the yolk over the bearing surface. If the joint fits inside the yolk now, you simply need to remove the one cap. If not, both caps (opposite each other) need to be removed. Gently press together and repeat for the other caps.
It can be a bit sketchy putting them back together. Just ensure everything is lined up and straight. If it isn't sliding together nicely, it isn't lined up.