As I do this as my very first "real" 3D print project I learned allot during this.
Axle_rear_Pinion_Ujoint gave me the most trouble as I repeatedly broke the top part during my attemt to screw in the grub screws. I finally printed them "upside down with support" which worked best for me.
As you can see on the second picture I also broke a half axle as I got carried away and played with the freshly assembled part a little bit too intensive :) This is when I realized what MrCrankyface meant when he said that longer screws will add to the sctructure of the part. I am using longer screws there now and till now no more breaks.
I also run a full threading process on all holes before attempting to use screws. Bought a tap and I am very happy with the results. Without tap even with the upside down print I needed multiple attempts to successfully mount the U-joint parts.
Also I found that my printer was very inaccurate and I managed to fine tune it to get better results. What I saw is that useing the grub screws in the U-joint setup, I had not enought space to thread them in deep enough to make them "dissapear" for the rotation to be smooth. This is partly related to the axle housing being printed without support I guess.
Well, I shortened the grub screws and it works for me, but you maybe want to use support for the axle housing.
I used 80% infill on all load bearing parts and 40% infill on the housing.
When I started the ball bearings did not slide smoothly into their position, this was also due to my printer being inaccurate. With my improved setup I can simply slide the ball bearings over like in the manufacturing videos from MrCrankyface.
MrCrankyface, thanks allot for this, I learned very much here.
40% Infill for the axle housing
80% Infill for the load bearing parts
Axle_rear_Pinion_Ujoint. Printing upside down with support worked for me.