So, there’s a lot of information rolling around how to “properly” convert your spring under Jeep to spring over. After contributing to a thread on one of the many jeep forums, I decided it was time to take the info I’d gathered, and eventually implemented, and put it in one place. This isn’t a how-to, or a start to finish install. It’s just a brain dump of what I learned, and what worked for me. My build was on a YJ.
SOA
Crash course time. Spring Over Axle (SOA) is just what it sounds like, springs go on top of the axle. The Jeep YJ, and CJ came from the assembly line with the springs beneath the axles. This was done for a number of reasons. One of them was to combat axle-wrap. Remember that. Another term I’m going to throw around a lot is Spring Under Axle (SUA).
Issues
Axle Wrap
Moving the springs on top of the axle gives you a wonderfully performing suspension, except for one thing. Axle wrap. The torque of spinning your tires causes your axle to “wrap” your springs around the axle as the axle torques. There are a number of solutions for this, I’ll cover a few.
Steering
Moving the springs above the axle causes one un-deniable issue. Steering linkage. The passenger side, where the drag link connects to the tie rod. Works perfectly when SUA, but when you move the springs above the axle, the drag link hits the passenger side spring.
To fix this, there’s a few solutions. There’s “Crossover” steering, and “hi-steer”. The stock D30 does not support hi-steer as it came from the factory. So you have a few options to consider. I’ll cover those as well.
Drivetrain
This isn’t really SOA specific, but it IS short wheel-base vehicle related. Have you ever looked under a pickup truck? Notice how long the driveshaft is? Several feet, maybe yards depending on the truck. Now look under a Jeep. You have about a foot and a half between your tailcone and your pinion. That means that it doesn’t take much to put your driveshaft at a really steep angle. Steep enough, and you have binding in the u-joints. This causes an annoying vibration in minor cases, which leads to damaged u-joints. In extreme cases it flat out wont work. Your driveshaft ends up too steep and the ears on your driveshaft can even contact the yoke on either end. This is of course bad.
Solutions
There are a number of solutions to all of these issues. Some cheap, some not so cheap. I’ll try to cover as many as I know about. I wont be linking products, just explaining options and benefits/draw backs.
Axle Wrap
Most of the solutions here involve preventing the axle from torquing. There are also a few tricks that help matters.
Some shops sell pre-fabricated spring perches that are really long. This is supposed to prevent axle-wrap by lengthening the perch. This makes the axle a little less likely to twist by extending its contact with the spring. I ran these myself. They did not solve the problem on their own, but they seemed to help.
Traction Bars are a low-tech solution. Also called ladder bars. They’re essentially a triangular tube structure that attach to the top and bottom of the axle, then to the frame. This, if you think about it, is the brute force method of preventing axle-wrap. However, it also doesn’t follow the arc of your springs correctly, which causes binding. They do a great job of preventing axle-wrap.
Bambar, this is a neat idea that I first ran across on Jeepaholics Anonymous. I believe it actually originated there. Anyway, it’s the same concept as the traction bar, except that it’s attached to the center of the axle housing instead of at one end or the other. It’s a really neat concept.
Springs, there’s two little tricks here. First you can take the main leaf, the one with the eyes, from a different spring pack, cut the eyes off, and add it to your leaf pack above the main leaf. This will add strength to the spring pack, without significantly changing your spring rate. The other option is reverse-eye springs. They supposedly help, I do not know why though.
Steering
There are three solutions here. All of which do the trick. Each of escalating expense and performance. First is a bent drag link. Next is crossover, or over/under steering, and then there is true high steer.
The lowest tech and cheapest method is to bend your drag link into an ‘s’ so that it clears the passenger side spring. I’ve seen this done. personally, i think its a bad idea. This weakens your steering, and changes the geometry.
Crossover steering takes your drag link, and moves it above your spring, leaving the tie rod where it is stock. This is the route I went when i did my SOA, it has drawbacks. Mainly two. First is that your D30 is not built for it. You have to drill and tap your passenger side knuckle, or replace the entire knuckle depending on what kit you buy. The other is that the tie-rod is right there in harms way out on the trail. Once you’ve modified (or replaced) your passenger side knuckle, the drag link is then attaches to a new mount provided by the new knuckle or bracket. It works, its cheap.
High Steer replaces both knuckles with modified knuckles, which move all of your steering components above the springs. This is optimal, but expensive! It’s really not worth the expense for a D30, if you’re going to go this route, replace your axles, you’ll be happier.
Drivetrain
You have two routes here. First would be to lower your transmission/tcase with a transfer case drop kit. This angles the drivetrain so that the rear driveshaft is at less of an angle, making it a little less harsh. The problem here is, you lose ground clearance, right where it matters the most, under your belly. This affects your break over angle. I ran this way for years while i was still SUA, I don’t recommend it.
The other option is to install an SYE kit, or replace your transfer case with something with a fixed yoke. this cuts inches off of your tailcone, giving you more room for a longer driveshaft. This is in my opinion the right solution. The SYE is usually stronger, and less prone to failure. It also makes it possible to remove your rear drive shaft, and drive under the power of the front axle in the event of a failure, without leaking your tcase fluid all over the trail!