I've been searching through threads about using a '40 Ford front spring on a spring-behind rearend setup on a Model A. I'd like to verify a couple things and ask a couple others. My trusty (?) Speedway Motors catalog shows dimensions on Posies springs for '40 Fords. For a un-split wishbone they show an eye-to-eye length of 39" with 42 3/8" perch centers. The '40 front spring I have is only about 35 1/2" eye-to-eye when laying on the floor. Would it be typical that it would need to be spread as much as 3 1/2" to hook up the shackles.....I'm thinking that's reasonable. I'm thinking using the 42 3/8" perch center width would be an appropriate width to position and weld rear-mount spring hangars to the rearend? My '40 front spring has 11 leaves including the second-from-main leaf that does a partial wrap around the main leaf eyes. I figured those two would be the foundation to build a spring pack, but on a fenderless Model A Coupe, what might be a good starting point to give a decent spring rate for the weight of the rear of the car? Numbering from the main leaf as being #1, would it be reasonable to then stack up #2 (partial wrap around main leaf eyes) and then #'s 4, 6, 8 and 10" for a 6 leaf spring pack? I just used the possible leaf #'s as a starting point for discussion. Once the approximate spring pack is chosen for a starting point, how much arch would remain when a fenderless Model A coupe is lowered on the wheels? For sake of measuring, let's say from the spring eye centerline to the bottom of the main leaf. Knowing approximately how much the spring would compress and flatten in load would be critical to ending up with a ride height close to what is desired. I do realize that a leaf or two could always be added or taken out to fine tune the ride and ride height. I'd just like to start as close as possible. If someone would have some "real world" numbers as a how-to on this kind of setup, it would save a lot of trial and error and re-work. I guess it's kind of lazy of me, but I figure why re-invent the wheel? Simple approach would be to s**** the spring behind and just use coilovers, but I'd like to stay a bit more traditional if my tentative build actually takes place. Thanks, as always, in advance. Lynn
I would use a So-Cal spring, with perch centers of 44-1/8". A far better ride than the 40 front spring.
For best results, you should measure your spring correctly. Measure from eye to eye, over the arch. This will give you the absolute longest that your spring will elongate to. Your spring perches should be about 1 1/2" farther apart than that dimension. Your plan of using the first two, then every other leaf is a good one, just make sure you use the very top one also. For years, when setting up a ch***is, we would use just the main leaf mounted on the axle to established ride height. The main leaf supporting just the frame would usually be pretty close.
The '40 spring setup used on the rear of a model A that I am familiar with use a flat rear crossmember and not the original. You didn't mention what your plan was.
on a '40 ford axle the spring perches are cast into the axle bells. The wishbone mounts make no difference to the width of the spring hangers? Are you getting confused with '40 ford and '35/'36 ford? '35/'36 wishbones have the spring mount on the back of them and splitting the wishbone would affect the width of the spring.
Jmountainjr....Fabricated frame extension and flat crossmember. Part of my questioning is to determine how much Z needed to get the stance I'd want. Hoping to keep it minimal depending on how the spring will act. weemark...not a '40 rear spring. A '40 front spring to be used on a S-10 2WD rearend. Lynn
raven...are you saying the bottom of a new rear crossmember would be 3" above the top of the Model A frame rail? Put another way, if I were to use 2" X 3" rectangular tubing with the tubing "laying down", that would put the top of the new crossmember 5" above the top of the frame rail. Just wanting to know if I'm on the same page as you. Lynn
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