if a 37 ford straight axle is angled 7 degrees back should I angle the spring the same? this is going to be a spring behind setup. I did a search but I know I didn't put in the right search words to find the answer.
Are you planing to mount the spring to split bones? Usually you do have to mount your cross member with the degree you hope to achieve. HRP
Be patient. Put every thing together. See what it looks like. If the caster ends up any where between 4 & 7 degrees wait to be able to take it for a spin to see how it handles, then go from there.
Yes, to avoid spring bind at the perches and shackles, the axle and the spring should be at the same angle. Spring-over or spring-behind, no difference.
Your spring should be mounted so that its flat surface is parallel to the ground. The spring carries the weight of the vehicle. This weight of the vehicle is perpendicular to the ground. By using a swivel style perch mount you will be able to adjust the caster curve that you wish without effecting the spring bind or the spring shackle twist.