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I have searched all about SOA and read every where about axle wrap. What exactly is wxle wrap? Also would a trac bar help on an SUA? Thanx people. <IMG SRC="smilies/usa.gif" border="0">
 

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I just had an intimate encounter with axle wrap with my new Spring over.

When you use flat springs that are soft and work well in a Spring over configuration they will bend under power and make the pinion point up and bind.

You can break a pinion or in my case a driveshaft in the progress.

Spring unders do not have this problem because the arched spring under the axle housing does not allow much movement.
 

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Besides using softer, flat springs in a SOA, the other reason that SOAs are associated with axle wrap is that the reason people do them is to run bigger tires. Bigger tires put a longer "lever" arm on the spring and make them more likely to bend as long as the tire doesn't slip. Just moving the spring alone from the bottom to the top doesn't matter, as it has the same torsion rate clamped on top as on bottom. I was dumb enough to actually measure this and there is no difference in spring deflection just due to location.

So to answer your question, if you run the same springs and tires, you won't have any more problem with axle wrap SOA as you had SUA, but it you run a softer spring and/or larger tires a traction bar might be a good idea.

[ 10-03-2001: Message edited by: Pin Head ]
 

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can some explain in some detail the issues of military wrap and its effects when you flip the rear springs? my understanding was this is the force applied when you send power to the rears, and if you have your springs set up right, if you break a main, this force will push the broken end up into the frame, so you can still limp back. if its wrong, the spring will want to pull away from the frame and your f*cked. what am i missing and how does this work. i dont understand fully the replies in the flipped rear springs post, thanks in advance, Matt <IMG SRC="smilies/biggrin.gif" border="0"> <IMG SRC="smilies/usa.gif" border="0">
 

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In short, the military wrap spring is located in the 2nd position on the spring pack, directly below the main leaf. The military wrap of the second leaf wraps loosely but completely around the main leaf eye. In the event you snap a main leaf, the military wrapped second leaf will continue to keep your springs and axles in their proper location to allow you to limp home from the trails. Without this military wrap, the spring has NO way of remaining attached to the solid mount end, and you will be stuck waiting for a replacement set of springs to get you out.
 

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Oooops...to answer the original question.

Axle wrap occurs as power is applied thru the driveshaft to the pinion and then rotated into power into the axleshafts. The resistance of the tires to the ground surface causes the pinion to rotate up rather than transfer that power directly to the ground. Soft springs accentuate this problem, and when the vehicle begins to "hop" a bit due to the low tire pressure and limited traction surfaces we run on, the springs will oscillate and the center section nose/pinion/flange/whatever will rotate up and down rapidly. GENERALLY, you will go BOUNCE, BOUNCE, SNAP....been there, done that, twice. Steep sand hills are a great way to bust pinions....

Oh, and the torque applied to the springs is identical on SUA and SOA applications....its the LOCATION of the torque that creates additional spring wrap.

Terminology: A TRAC BAR is used to locate the axle side to side, much like what's on the front of newer Jeeps, early Broncos, and many many other vehicles. A WRAP BAR is generally a triangulated unit designed to prevent the rotation of the axle housing while still allowing free suspension movement. I've got one teched on my website, and there have been many others done. NONE are pertect in their design, however I have no complaints with mine!
 
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