'41 and earlier Fords had the spring and shackles arranged so that the shackles put the spring in tension, end to end. The spring in its free form is quite a bit shorter than the distance between the perches less the lengths of the shackle. To install or remove the spring here usually requires a "spreader" which pushes out on the ends to flatten it out a bit and make it long enough to engage the shackles. When a spreader is used in manner, there's a lot of force involved which can do lots of damage (particularly to the person using it) if it slips or breaks or whatever. When this spring / shackle arrangement has the weight of the car on the spring, the shackles are on about a 45º angle. Increasing the load causes the spring to flatten out a bit making it effectively longer and making the shackles a bit more vertical. Possibly, they felt that this arrangement wasn't too effective at keeping the body from swaying or leaning when cornering. So, in 1942, they pulled the perch mounts in a bit and lengthened the spring somewhat, so that even with aload, the shackles hang straight down and there's no longer any end to end tension on the spring. Now, the body is free to do all kinds of side to side floating, rocking and rolling. To combat this, they added a Panhard bar which runs horizontally from a bracket on the frame to the perch mount on the other side of the car. This allows the body to move up and down with load and bumps etc and the Panhard bar keeps it from moving sideways. Also, the shackle in the spring was given a large rubber bushing so the spring end of the shackle is a different animal from the previous construction. IMHO, of course!
