There are many different lifts out there on the market these day's. Companies like Rancho Trail Master, Skyjacker, and Pro-Comp have been around for a long time. These kits looked good but the ride quality was something to desire for. (Kidney belts not included.) Old Man Emu was the first company to design a kit that was not only looked good but performance good, too. Their springs were soft allowing a stock like ride while still adding 2.5 inches of lift. There was one problem though. If you wanted more lift you were SOL. Soon after, Rubicon Express filled the need with their Extreme Duty line. These kits came in 2.5 and 4.5. With +35 tires common place there was a need for more.
Now RE also produced a 'Do-It-Yourself' Spring Over Axle (SOA) kit. The SOA reuse the stock leafs so the Jeep had a ride equal to stock. Since the axle housing was now below the leaf spring, anywhere from 5-6" of lift was achieved. Many people consider this the best lift option for leaf spring Jeep without going to a custom multi-link setup.
Now people have been doing SOA's well before RE, but they were the first to package it so a person could buy everything they needed at once. The kit came with the correct length shocks, brake lines and spring perches needed. The only thing the buyer had to supply was the welder and the talent to use it.
Now the SOA does have some drawbacks. Since many use old stock leafs, owners were finding their springs wear out more frequently. Some people started to add extra leafs to the spring pack which boosted in spring rate a bit. Another option was to use a 2.5" lift leaf pack. Because of this problem RE came out with a specially designed 1.5" leafs to help combat premature sagging.
Some thing to consider with a SOA is stability and control. The softer leafs will allow more body sway which can make for an interesting ride on off-camber obstacles. SOA in the rear typically leads to axle wrap where the torque from the drivetrain will twist the leaf spring. This causes a loss in traction and increased wear on the leaf pack. To offset this many add some type of traction bar.
This begs the question; why not use a hybrid of the two? What you get is added stability and no axle wrap while still having decent suspension travel. This type of thinking gave birth to the SOA/SUA setup. A SOA is used up front for added suspension travel while the rear is lifted with SUA for its stability and ability to combat axle wrap.
With a SOA up front, an equivalent amount of lift is needed in the rear. This means a minimum of 5 in the rear. Since 4.5 is the tallest mass-produced leaf, custom leaf springs from places like National Spring Company of Santee, CA or Alcan Spring of Grand Junction, CO would be a good choice. There is another option though. For those who already happen to have a 4" lift spring available, you can still squeeze out a bit more lift. The easiest option would be to use a 1-1.25" shackle lift. Now a lot of people don't like this idea since you will change your pinion angle and reduce your departure angle. Not to mention the longer shackle has to be 2" longer then the stock which could weaken the shackle if not accounted for. Longer shackles tend to have an 'H' design so they are stiffer which means they wont be as flexible as the stock shackle.
The other option is to weld on a new shackle hanger below the frame. This will still rotate the pinion and will change the departure angle but will allow the use of a stock height shackle. The rear hanger needs to be 2.5" wide which is the same size as the CJ's rear hanger. CJ's have bolt on hangers so they are a ready source of parts. Warrior, MORE and other make replacement hangers for CJ's that will work fine on an YJ.
Depending on your setup, you will most likely need to convert the transfer case over to a SYE and perhaps a CV driveshaft if the angle is bad. The Jeep we used had a XJ Dana 44 rear axle which brought the pinion high enough to still use the stock driveshaft. Sooner or later this will be replaced with a fixed yoke though.
There are some other things you will need to do once the rear is lifted. The brake line will need to be extended. Also the emergency brake cable on the driver side will need to be changed. Some drill a lower hole in the e-brake bracket on the frame. This allows for a bit more drop. Another option is to exchange the cable for one that is longer. One source is from Cherokee, TJ or Grand. These use a center-pull E-brakes with two equal length cables. Swapping out the short YJ cable for the new one will give you an extra foot in length.
With the easy stuff is done the front will need some attention. Stock rear 5 pack leafs were used on the front to raise the spring rate a bit. Stock rear leafs are 5 pack while the front are usually 4 pack. Perches are a bit of a problem on the stock Dana 30 housing. The driver side perch needs to sit over the lip of the housing sleeve. This can be fixed two ways. One is to reshape a standard perch to fit over the larger arch in the housing. The other option is to use specially designed perches from RE or MORE. These perches are slightly offset to they are able to sit on the axle tube.
Now that you have the perches, where do you mount them? Well, we did it the easy way and put the new perches parallel to the old ones. First we leveled the pinion then measured the angle for the stock perches and duplicated them for the new ones. This kept the stock pinion angle so the U-joints would be happy. The stock steering works fine with a 1" dropped pitman arm and the RE perches on stock leafs. The problem area is the drag link contacting the passenger side leaf spring at a full turn. If this happens then a slight S bend in the drag-link might be necessary.
Once the perches are welded in place, everything can go back on. To extend the front brake line there are a few options. The easiest would be to switch over to braided stainless steel lines. A cheaper option would be to use longer OEM lines from another vehicle. 1987 3.4 Ton Chevy P20 or similar will add 4 compared to the stock lines. A cheaper solution would be to relocate the stock lines under the frame. This adds 4-6 of length to the stock lines.
http://www.4bangerjp.com/forums/viewtopic.php?t=11Here are some things to note. The suspension and ride will be soft. With the added lift and extra weight, the Jeep will pitch forward under hard braking. There will be some bump steer if you use the stock steering. How much will depend on the height of the springs and how bad the front end geometry looks. It might be good to reconnect the track bar for daily driving. Now that the suspension is softer and the Jeep is taller there will be more body roll. You may want to reconnect the front sway bar to make it a bit more drivable. Braking can be interesting especially with a Detroit Locker in the rear. In short, take it easy until you're used to how the Jeep handles again.
