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Technical Question about mix-matching springs ( Model A Roadster )

Discussion in 'Traditional Hot Rods' started by crazycasey, Jun 6, 2021.

  1. So, I’m trying to get the rear of my Model A chassis down a bit, and I’ve got a couple of different springs at my disposal. One, which I believe is a reproduction, is a 6 leaf reverse eye spring with a very tall profile. The other is a spring that I bought as an original “roadster spring”, but might just be something that somebody re-contoured at some point. The reverse eye spring is what was on the car already, and I was going to use it with the Tardel technique of cutting down and swapping underneath the top three leaves.

    But after I yanked the top of the spring pack, and laid it next to “roadster” spring, I noticed exactly how much lower that spring seems.

    01819BAF-B3BC-4BD3-A742-51E96575FDD8.jpeg

    So what I’m thinking about doing now, is using my reverse eye main leaf, followed by the the #2, and #3 leaves (counting from the main leaf up) from the “roadster spring”, and then moving the top three leaves, cut down, underneath, as per the Tardel book. I’m not really worried about the car being too low.

    Here are the two “roadster spring” leaves on top of the reverse eye main:

    41586E11-6AB3-4534-B4BA-BA16DE3A3FAE.jpeg

    My worry, I guess, is that the shape of those middle two leaves is going to put too much stress in one spot on the main leaf, since it hasn’t been contoured to match. Is that a valid concern, or will it just sort itself out?

    Thanks,

    Casey
     
  2. Nevermind...I think I answered my own question:

    C7B33217-DF1A-481E-831F-D8696B5F1890.jpeg

    While I’m sure that with weight on the car that main leaf would flex into the next two, I think that it would absolutely be putting all the pressure in one place (well...two places), instead of using the whole length of the spring. Somebody please correct me if I’m wrong. I don’t think think this is a good idea, though...
     
  3. At first glance it looks like you have an A spring and a T spring. Two different shapes.
    Ford used different leaf counts between heavier and lighter cars, but the shape was all the same.
     
    stillrunners likes this.

  4. I thought there was a width difference between T and A, no?
     

  5. lake_harley
    Joined: Jun 4, 2017
    Posts: 2,160

    lake_harley
    Member

    T is 2" - A is 2 1/4"

    Lynn
     
  6. I'm pretty sure roadster springs have a different arch.
     
  7. That’s what I thought. These are both 2-1/4”.

    Different than this spring, or different than a coupe spring?

    Regardless, this seems to be a self-fulfilling prophecy; I assembled the spring how I mentioned, and it was bottoming out with just my weight bouncing up and down on the rear crossmember. And comparing main leafs, this “roadster” spring would need wider perch centers to have any significant travel.

    Guess I’ll do the reverse eye spring per Tardel.
     
  8. Last edited: Jun 7, 2021
    crazycasey likes this.
  9. woodiewagon46
    Joined: Mar 14, 2013
    Posts: 2,269

    woodiewagon46
    Member
    from New York

    There were six different rear springs used on the Model A during it's production run. All have the part number A-5560 followed by a letter, B thru F. The roadster spring had seven leaves and the part number is A-5560-C. It came stock with a "dummy" leaf or spacer making it eight leaves thick to fit into the rear crossmember. The number four leaf was made of thinner stock measuring .220-.230. Depending on the body style the springs ranged from seven leaves to 13 leaves that were used on some Canadian cars. There is a complete description with measurements in the Model A Judging standards as every spring has different thickness of leaves ranging from .220 up to .310.
     
    warbird1 likes this.
  10. lake_harley
    Joined: Jun 4, 2017
    Posts: 2,160

    lake_harley
    Member

    FWIW...here's a photo of a T spring I just sold. 2" wide and 43 1/2" eye to eye width, and 12 1/4" height measured from a line between the eyes to the underside of the spring pack. Seems to me that the spring you have in your first photo, if it's 2 1/4" wide, is one that someone re-shaped to resemble a T spring. I hope this helps in some way.

    Lynn


    20210604_153135.jpg
     
    panhead_pete and crazycasey like this.
  11. That diagram is super handy...

    Interesting. So, neither of my spring packs are the correct thickness then. The aftermarket pack has 6 leaves all 0.260” thick, and the T-wannabe spring has 6 leaves of varying thickness.

    That’s exactly what this is a copy of Lynn...thanks for posting it.
     
  12. So, if I had moved the top three leaves of my 6 leaf pack underneath as per the Tardel book, my new pack would only effectively be made up of three springs (doing the suspending), and the correct thickness once I steal two more “dummies” out of the faux T-spring. I’m thinking that might end up being too soft. Has anybody played around with that few effective leaves in a roadster? I’d like the car to be low, but not a bottoming out mess...
     
  13. I've played around with a lot of combos. On my truck. My old coupe. And a roadster
    4 seemed no way. 5 seem soft. I think 6 is the magic number on a roadster and maybe a fenderless A coupe . I run 7 in my truck and have still hauled a flathead v8 in it. It has an A springs.com reverse eye.

    I could be wrong. But from what I remember A-springs.com offers a reverse eye spring for roadsters and then one for all the other body styles. That is because of the arch difference.
     

  14. So, when you say 4, you mean 4 long “effective” leaves (which is what is lid out in the Tardel book)? And you’re saying that was no-way too soft!?

    Was that starting with a roadster spring? And was that OEM or aftermarket?

    Sorry to ask so many questions. Basically, I only have 6 springs right now, and the top one isn’t doing anything to speak of. The rear end doesn’t move when I bounce on it with my 200-ish lbs. Moving it underneath the pack will lower the car a 1/4”, but won’t really affect the rate. But this is probably also a coupe spring...pretty high arch.

    I’d say I’d just experiment, but I only have so many leaves to cut and move under before I’m past the point of no return...
     
    Last edited: Jun 8, 2021
  15. alchemy
    Joined: Sep 27, 2002
    Posts: 20,407

    alchemy
    Member

    Pretty sure you will need at least six leaves in your spring, even if it's just a light roadster. Yes the top short leaf is needed. Finding a matching set of leaves is very important, as if they don't have the same arch, each leaf will spend half it's time working against the other arch, and the rest of the time holding the car up. Since Model A springs have a bunch of different alternatives, I'd recommend starting with a known good spring rather than piecing one together.

    Now, this idea of cutting up leaves to use as spacers is absolutely dumb to me. I don't care who originally preached this as the "best way", it's a waste of good material. As you know, you are going to have to do some experimentation to get your car riding right. What happens when you need that leaf back that you cut up for a spacer?

    If your lower tie bars on the spring clamps don't reach far enough up to firmly hold the spring, then add a little metal to the top of the tie bar. Cut a small rectangle of steel (1/4" thick , 3/8", 1/2", whatever) the same size as the bar, tack weld it to the top of the bar, and tighten it up. If the car rides smooth and sits right after you have a few hundred miles on it, then pull the tie bars out and make that weld permanent.
     
    lake_harley likes this.
  16. I hear what you’re saying about wasting good material and getting stuck without enough leaves, but I’ve got to disagree with the 6 leaf minimum assessment, because that’s the way I was running this chassis previously, with a rumble seat COUPE body on it, and not only did it sit like a 4x4, but the damn thing was rigid, and bounced over bumps.

    Here it is empty (note this is how it sat with a frame width rear step and a comically large 7.50x16 rear tire):

    75A55463-ED07-406D-941A-C2EE23DD21D3.jpeg

    And here it is with 500 extra pounds in it (no noticeable change in ride height):

    6AEC239F-326F-46B9-8398-05C87F5E6534.jpeg

    Again, that’s 6 leaves, straight up. And I would have thought the thing was bound up, but I pulled the spring pack apart and set the frame on the main leaf, and it has a full range of travel with minimum effort. But perhaps the leaf contour is just too aggressive. I have no idea who made this spring...

    But I’ve since switched to a 7.00x16 rear tire, and installed a dropped front axle, so now the chassis has a massive rear fender opening gap and really bad stink-bug rake. I haven’t dropped the roadster body on it yet...

    When you said 6 leaves, were you talking about 90 year old originals? Maybe they’ve sacked out some over the years...there sure do seem to be a lot of folks on the HAMB following the Tardel book like it’s the (actual) Bible, and that recipe is four main leaves with the originally lower dummy and top three cut down leaves underneath. And he’s talking about doing this on an original roadster spring...and potentially “profiling” the spring a bit lower from there, if necessary...
     
  17. Yes I thought 4 was way to soft....

    One thing that really makes a difference in performance is I have chamfered, polished and graphite spray to all the leaves. When they move easy and as intended I think they need a little more spring than say just bolting 4 or so together. With my truck set up like the Tardel book, and my spring prep i could cycle the rear end through the whole range of motion with my weight. I'm 275 pounds.
     

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