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soa

Discussion in '40- & 55-Series Tech' started by rusty40, Mar 10, 2003.

  1. rusty40

    rusty40

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    when doing spring over on a cruiser it seems alot of people use the dodge spring perches are they bad for axle wrap?

    I was thinking longer perches made from 2 1/2" sqaure pipe with the cutouts for the axle tube would make axle wrap less likeley anyone tried this?? I was thinking maybe 6 inches long might work good?
     
  2. woody

    woody Internet Fireman Staff Member

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    Axle wrap should be controlled by a wrap bar, not by the spring perches.
     
  3. Halo3

    Halo3

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    To go along with what Woody said...and beings that I keep seeing a lot of little threads on this...

    Axle wrap is caused by the axle trying to spin in the opposite direction from the direction of travel. The primary concern in this is that the top-most leaf of the spring pack gets tweaked pretty bad.

    In a SOA application, your spring perch is underneath the shortest leaves of the spring pack. Thus, longer spring perches will have little, to no, impact on minimizing the deformation of the upper leaf/leaves caused by axle wrap. Which is why SUA vehicles are less susceptible to axle wrap.

    Now, if this is still clear as mud, follow along with this practical application excercise...it was passed down to me by an old time four-wheeler & hot-rod builder. It is a generic mock-up of a live axle w/leaf springs.

    Get two rubberbands (thick ones are easier to use & better for the visualization), a pen or pencil, and a little bit of tape, glue, or rubber cement.

    Lay the rubberbands down on a flat surface, about 2" apart from each other. Now lay the pen or pencil across the rubber bands; this should form an H-shape. Then you will want to glue or tape the pencil to the rubber bands.

    Once you have everything assembled, and the glue or rubber cement has cured, loosely loop the rubber bands around the thumb & pointer finger of your left hand. Now, ignoring the top part of the rubber band, think of the bottom arching portion of the rubber bands as your leaf springs...with the pen/pencil obviously being the axle assembly. When you mash on the accelerator of a vehicle, there is some greater or lesser tendency for the axle to spin in the opposite direction of your travel. To simulate this, spin the pen/pencil a quarter turn or so, and watch what happens to the rubber bands. You should notice that the forward side...in comparison to direction of travel...will have a tendency to wrap up into an S-shape. The backside of the leaf spring will have the tendency to bow downward & outward....rear leaf springs typically have the shackle in the back...which helps minimize the S-shaped flexing that the frontside of the leaf/leaves experience.

    Hope that helps...
     
  4. rusty40

    rusty40

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    I guess I will be making a wrap bar

    I was just looking and the factory crossmember behind the t-case and it is rustin where it passes through the drivers side frame rail

    there is actually a hole thru at the bottom!

    maybee I should be repairing this or making a whole new one ::) anyone tried this yet?
     
  5. bernefj60

    bernefj60

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    Actually, this isn't *entirely* accurate.

    True, longer perches will not make as much difference as a traction (or anti-wrap) bar will. However, all things being equal, i'd go for the longer, square tube shackles rather than the dodge perches.

    Here's why.

    When we did the SO on my 40, we used con-ferr (i think - this was about 6 years ago) spring pads, and i remember thinking that they were awfully small. I also had some trouble with axle wrap.

    So, when we did the SO on my 60, we made our own out of square tube, and made them about 2 1/2 longer than stock.

    So, my perches in the rear extend about 1 1/4" further on each side than the orginal.

    So the question is: Does this prevent axle wrap. Well, i haven't had any trouble yet and I haven't found a good design or any need for a traction bar yet. I suspect when i finally break something, i'll have found the need.

    More than axle wrap, to me the larger pads help spread the load better. Which equates to better stability, etc, especially with a 60. With a 40 being so much lighter in the rear, i can't see how it wouldn't be a good thing.

    Just my .02, not disagreeing, just offering another perspective based on personal experience.

    Rob
     
  6. cruzer

    cruzer

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    There is no reason you can't fab one up. When you go with a Toybox you need to move the crossmember back if you use a 2F....sounds like a good excuse for a toybox to me :D...but serously you can make one that will work in there...as long as there is enough frame left to weld to. :eek:

    Stew
     
  7. Halo3

    Halo3

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    The reason I say that longer spring perches will have minimal effect on axle wrap is that the bottom leaf of a spring pack generally has more curve to it than the equivalent position on top of the top leaf. Given this, the main deterent that can be found is properly torquing the U-bolts to minimize the "rocking" that can be experienced, as you likely won't be able to tighten them enough to get the arched lower leaf to conform to your standard, nice, flat spring perch.

    One of my buddies got into this debate with me (we both know enough mechanically to be dangerous to ourselves...if not others ::)) while I was doing my 4" Skyjacker lift. In the end, we took a couple pieces of cardboard, traced & cut-out the arch of the lower leaf, and then positioned it in its respective place on the top of the upper leaf....you could see the decidedly "harder" curve of the lower spring leaf....i.e. the top leaf has a "flatter" surface to mate with the spring perch.

    Now, having said all of that, there are custom SOA spring packs out there that take this into account, and therefore have nice flat mating surfaces built into the lower leaf. Alternatively, many four-wheeling shops will custom make spring perches that match the arch of the lower leaf...once again, making for a nice mating between the two.
     
  8. 73fj

    73fj Tho at sumbitch in ayer!

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    i used 12" perches on my soa. to help control axle wrap i installed the overload spring from a mid 90"s ford f-150 to give me a flatter surface for the perches to sit on. with a 350 4.56 gears and a big right foot i have had zero problems