Re: BigKev's 1937 115-C Convertible Coupe

Posted by DavidPackard On 2023/1/12 18:35:04

The comment about the same springs is odd to me in that the parts books has two different springs for all 22nd to 54th series cars. Not the same spring for every series car, but for any one brake configuration there were two different springs. Having said that once the material is selected there are only a few characteristics that make one coil spring ‘stiffer’ than another. The wire diameter, number of coils, and mean diameter of the coils are variables that change the fundamental stiffness (pounds force per inch deflection). Since there is no reason to have different spring rates in a brake drum application I would bet the stiffness is the same for both the primary and secondary application. The only variable left is the initial preload which is determined by the difference between the installed and uninstalled length of the spring. The only difference between the two springs may be the uninstalled length . . . and not by a lot . . . maybe something like 1/8 inch.

If I was in the business of making brake springs I would advocate using the same stiffness (wire, coil count, outer diameter), and make the difference in the uninstalled length. In that way I could have my winding machines running full speed ahead, and manage filling purchase orders at the hook bending production step. Let’s not forget the different color paint. The ’54 shop manual associates an orange spring for the primary shoe, and a yellow spring for the secondary shoe. Some seventy years later I wouldn’t expect the supply chain to use the same Packard color codes, but if there is a difference in the springs I would expect two different colors . . . and that difference may only be the length . . . shorter is the secondary.

The artwork that Howard posted (bottom of page 209) shows the ‘extra’ spring on the secondary side, so if the ‘extra’ brackets are on the trailing half of the backing plate then I think those ‘extra’ springs are there to ensure the primary shoe moves first.

dp