Leaf spring wheel alignment

[Dan Case]

We have measured the wishbones front and rear for four original cars and they were very consistent. All the pieces were laid in fixtures for welding so there should not be a lot of variation.

I have measured the front halves of three chassis and except for what people did to them they were very consistent. Again, all the pieces were clamped into fixtures for welding.

We have measured the road springs also. The eye to eye distance with the main leaves held flat agrees with what A.C. published when the cars were new. The only variable in spring assemblies on a work bench beyond a few thousandths has been the in free camber. All the decades old springs had slightly less free camber than what A.C. described new.

In a period letter to a customer A.C. described how they used a long straight edge against brake rotors front and rear to test suspension alignment during assembly.

For factory road racing front spring main leaf pairs were shortened to obtain a camber the driver and crew desired within some kind of tolerance. For drag racing the lengths of both springs were changed to suit desired outcomes. I would imagine that those making “adjustments” as their every day job had a real good idea how a change in length X changed camber Y.

In well used cars it is not rare to find the four u-bolt holes in spring towers deformed, especially in any car that has been crashed. Deformed or wallowed holes allow users to install road springs crooked such that wheel base on one side is short and one is long. It also messes up other geometries. Shelby American’s racing solution was to put the springs exactly where they wanted them and then weld in hard stops to prevent the springs from twisting laterally on top of towers.

Front wishbones are not very strong and do not really need to be other than they flex easily. How easily, I straighten slightly deformed ones with some dowels and hand /arm pressure. Arms can be flexed and rod ends rotated to get back to factory dimensions in most cases. Shelby American stiffened racing ones by adding cross tubes to make triangles out of the assemblies. That stopped most of the flexible nature of the front wishbones.

There was another issue and that was sometimes the center bolt in a spring was not actually in the center of the eye to eye dimension. I have found that in two springs with offsets. Fortunately the clearance holes in towers are just that clearance holes. I was able to slide errant springs to one side or the other to get the eyes on each side equidistant from the frame.

Don’t forget that the whole chassis in an original Cobra is part of the “suspension”. If all four corners suspension parts were rock solid the chassis as originally made would be flexing all the time in between the corners. Many original car owners have added some type of sleeves full length of their main tubes. That change is a big one for original car dynamics.

Tires. Tires, street or race, before the 1970s were a serious limitation. A box stock street car could not get traction and race cars were not much better. To a point having more power or a better suspension would not have helped on hard rubber skinny tires. Whether the camber was exactly X° or X±1/2° was probably not an issue. I have an old note page from a privateer racer. He stopped if he got within ½° degree agreement between left and right sides front and rear. (Yes, people use to check and tweak caster and camber. One racer published a how to article to make small caster changes in Cobra suspensions front and rear in his club magazine long ago.)

One original Cobra box stock versus one with sleeved frame, hard stopped springs, triangulated front wishbones, custom stronger than anything Shelby’s works did roll bar system, and shorter front spring to get some negative camber as desired are very different on the road and the harder the cars are pushed the more different they behave.