How much thought do you actually give to the leaf springs in your hot rod--that is, if your car even has them to begin with. Those who have their rods built probably wouldn't think twice about the springs, unless for some reason those springs were not performing up to par. But then that puts you back to square one and having to know the ins and outs of spring basics. That's where POSIES comes into the picture, as they've been working with hot rod leaf applications for years, and know a thing or two about springs.
For the most part, most people may take for granted what exactly a spring does. Basically, leafs locate the axle they are suspending, be it an I-beam or even a rearend. Secondly, the springs obviously support the weight of the vehicle, and in doing so provide the ride height. Lastly (in conjunction with shock absorbers, tires, etc.), they control the ride quality of the vehicle. Along with the performance aspects, they provide adequate stability and resistance to side sway and rollover, and resist cornering effects in turns.
Additionally, proper leaf springs are designed to transfer forces from braking and driving between frame and axle, as well as resist wrap-up caused by drive and brake torque, and, on I-beam type applications, maintain proper caster and camber.
Hopefully it's common knowledge that there's more than one spring for the various Ford I-beam/tube axle applications. First off, there are different OE lengths for Model T, Model A, '32, '33-34, '35-40, '41-48. That's a lot of different spring lengths to have to remember, but fortunately, POSIES has grouped everything together into two separate designations: '28-34 (for which they offer four different applications) and '35-48 (with eight applications). Okay, so that makes it a little easier, but just knowing what year chassis you have doesn't automatically tell you what spring you need.
Consider the type of axle you have--stock or aftermarket--and take measurements from perch centerlines, and that will narrow everything down for you. For the earlier years, most stock axles will measure out in the neighborhood of 36 inches, while different aftermarket axles will vary between 36 1/2 and 34 1/2 inches. Now, because of their makeup (spring in front), later axles measure differently due to various wishbone perch widths, from 36 1/2 all the way to 42 1/2 inches. Another thing you have to take into consideration is the use of standard or reversed-eye springs--do you have enough travel for lower, reversed-eye leafs or not? (You will need to factor in the actual drop of your axle, the weight of your engine, etc.)
On top of the tons of applications POSIES offers in transverse leafs, they also have their new Ellipta Slide Kit, a quarter-elliptic spring set perfect for old-timey hot rods with that dirt-track flair. The kit consists of a pair of rolled and tapered springs with Super Slide buttons, adjustable 4-inch mounting stubs, shackles, and hardware. The Ellipta Slide can be utilized for rearend use, as well.
Once you get everything all figured out, the knowledgeable staff at POSIES will keep you steered in the right direction with the proper spring for your application, and once you've got it mounted correctly in your car, look forward to a smoother ride from there on out. POSIES was grateful enough to supply us with photos and illustrations dealing with various spring options, measurements, and tips that should help you figure out the right application for your situation. For more information, don't hesitate to give POSIES a call.
For each application, Posies offers OEM-type springs with stock eyes (left); lowered sprin
A trademark of POSIES springs, the low-friction, moly-nylon buttons (sliders) aid in the p
Here's a handy diagram, courtesy of Posies, that should help you understand how certain me
To measure for a spring using your axle, measure between the centerlines of the spring per
To measure for a spring using the perches, measure between the centerlines of spring perch
Measuring for '35-48 springs is the same as measuring from perches. Although it must be no