In a front spring-over application,...
In a front spring-over application, the position of the spring pack complicates the drag link mount on the axle. Avoid running a goofy S-shaped bend in the drag link to attach it to the tie rod or steering knuckle. The only correct way to do it is to run some sort of crossover steering arm on the top of the passenger-side knuckle to raise the drag link mount high enough to prevent spring pack interference.
Christian Hazel Says
For me, the biggest advantage to doing a spring-over is the ability to run a flat leaf spring. You can get nearly equal compression and droop from a flat spring, allowing for a cush ride and some impressive wheel travel from a modest lift height. Spring-over setups that use lift springs scare me because the center of gravity is raised so much. I've never understood why a Wrangler or CJ needed to be lifted 7 inches or more unless all you're doing is going in a flat, straight line through a mud pit. I also like supple spring packs, such as the factory 5-leaf Wrangler rear springs. Granted, the softer packs exacerbate the axle wrap problem in a spring-over, but it's been my experience that nearly any moderately-soft pack you run is going to wrap to some degree when used with big tires. And if you're using a pack that's thick and heavy enough not to wrap, you're going to be limiting your wheel travel, so why not just go for an easier spring-under setup?
That's why nowadays I prefer a spring-under suspension to a spring-over. They're easy, with no need for a complicated crossover steering arm to accommodate the drag link, no traction bars to counter axle wrap, and a huge selection of ready-made off-the-shelf and custom applications available for the choosing. That's not to say spring-under systems aren't without their caveats. For starters, the more highly-arched spring packs will require longer shackles because the spring has the potential to grow much more than a flat leaf spring. You'll also need to be wary of your axle U-bolts and leafs, as they'll be more vulnerable to damage from trail obstacles. And the spring-under will still require nearly all of the same brake line, driveshaft, and shock corrections and considerations as the spring-over. But at the end of the day, a properly selected spring-under suspension can offer nearly the same travel and comfort as a spring-over setup, but with a whole lot less fuss and muss.
Pete Trasborg Says
For me, being a guy with a moderate income and an overabundance of Jeeps, the important thing is the ability to build the spring-over lift as you go. Yeah, we aren't supposed to talk about it, but the reality is most of us are on budgets, and building a little at a time can be the only option we have available. Once you accept the fact that to make it work correctly you'll likely spend the same as you would for a spring-under lift, you can move forward.
Consider the need for the fabrication tools such as a welder, grinder and reciprocating saw at the very least and right away you are in the $500-$1,000 ballpark. Or, maybe you just bribe a buddy with beer and pizza until the job is done. Even if you have all the tools and steel needed, you will still need longer shocks, longer brake lines, a slip-yoke eliminator, driveshafts, and so on. Buying that stuff piecemeal is more expensive than in a kit.
If you are just mud-running, you can get away with lowering brake lines, and relocating shock mounts, or doing away with them entirely. That is, until you've got the cash for the right parts. Look, it won't handle well on-road, especially with no shocks, but around town it'll be fine, and some poor handling for a little while is better than a blown motor from a deep mud pit.
That said, I agree with Cappa about blowing up driveshafts. I've done it myself plenty of times thanks to my short-term cost-cutting methods and just flat-out not running a traction bar of any type. The other thing with using stock leaf springs in a spring-over configuration is that the springs will sag pretty quickly, and while I can likely find stock YJ springs for free, I have gotten really adept at swapping them out, and, if you use new u-bolts each time like you should, there are additional hidden costs there.
I used to be a fan of spring-under lifts just because I could put them together as the bank account allowed. Now I'm more inclined to cut sheetmetal before going through with a spring-over conversion.
Longer shocks, brake lines,...
Longer shocks, brake lines, and swaybar links will be on the list for either a spring-over or spring-under suspension. You'll also need to match your shock length to your suspension travel, taking note of how much droop is permissible before your driveshafts bind or separate. The use of shorter shocks as a limiting device is acceptable, but don't forget the dropped bumpstops to keep the shocks from bottoming on compression.
Whether spring-over or under,...
Whether spring-over or under, a good spring pack will employ niceties such as these military-wrap main eyes, meaning the second spring wraps around the main eye spring for more resistance to axle wrap and a measure of security in case the main leaf breaks.
Running some type of U-bolt...
Running some type of U-bolt flip setup, such as this example from Dynatrac, can help keep your spring-under suspension from getting hung up or damaged on trail obstacles.