IO,
Your comments are always appreciated as they usually cause me to check my initial calculations to insure that we have not gone down a potentially dangerous path.
First, our car has a front end weight of slightly less than 400 lbs static, which would make each the load on the two rod ends that support the front of the car 200 lbs. The rod ends are 7/16 inch diameter with 7/16 shanks. This makes the thread root diameter of .390 inches. Using these loads and dimensions and the dimension from the C/L of the ball to the back of the lock nut is 1 inch, the maximum bending stress is 33,460 psi and using a material yield strength of 67,000 psi and tensile strength of 100,000 psi gives a safety factor to yield of 2:1 and to the material tensile strength of 3:1. This is based upon the normalized properties of 4130 at yield of 67,000 psi and tensile strength of 100,000 psi. Pretty standard material properties. Rough salt, pot holes etc could certainly provide the potential for these components to see loads possibly in excess of our estimated loads and possibly cause bending or in the worst case complete failure but these are not the typical conditions that we see at Bonneville.
We also keep a close eye on the rod ends for any corrosion, and keep them coated with Gibbs oil for protection. We also keep the extended length of the rod end to the back of the lock nut as short as possible to minimize the bending moment and we periodically change the rod ends to keep them fresh. We also only use rod ends that are of the highest quality and constructed from 4130 and have rolled threads. I do agree that using a rod end in the load configuration we are is not optimal but by using quality parts and sizing them to provide sufficient safety along with the proper cleaning and protection from corrosion and periodical replacement the application will work.
IO,
In response to your last post, the function of the upper triangular link is to proved lateral location of the axle and provide the upper link of a parallelogram (in side view) to located the axle and set caster. This link also sets the roll center height for the axle which is pretty meaningless, in my opinion, for a car designed to run in a straight line on a smooth surface. Maximum suspension travel is approx 3 inches which also limits any possible side motion of the axle on one wheel deflections.
Rex