One of the best parts of a YJ or CJ springover (SOA) conversion is the massively increased wheel travel. You get more wheel travel because of the axles' increased leverage on the springs, and also because you're moving the axles further away from the body of the Jeep, allowing you to run longer shocks.
Longer shocks are key. More than anything else, shocks turn up again and again as being the limiting factor in suspension travel. They bottom out, they top out, or both!
The physics of shock absorbers are pretty simple: the longer the body of the shock, the more extension it will have. And more extension = more wheel travel. To fit a longer shock into your Jeep, you can do two things:
On a YJ, the front shock towers are the type with an eye-mount on one end and a pin-mount on the other (aka pin-eye). These shocks aren't as common as the type with eye-mounts on both ends (aka eye-eye). In fact, the longest shocks from the Rancho line are exclusively eye-eye. They can be adapted to work in YJ's with the use of special pin-to-eye adapters, but these eat up some of that precious shock length. I made a pair of those adapters for a while after my SOA conversion, before I heard about another, much better option.
Turns out that F-series (F150, 250, etc) Ford trucks use a bolted-on shock tower that has an eye-type mount. These towers are very heavy-duty, stamped out of 3/16" or 1/4" steel, with a second thickness of steel where they bolt to the frame. Two bolts hold them to the frame, and no extra gusseting is required. Dead easy.
$30 poorer, I left Wasney's (a local Ford wrecker) with a pair of these puppies in hand. You can find them on pretty much any F-series pickup with front leaf springs. Trucks with front coils don't have their shock towers integrated with their coil mounts, so pass them by. Mine came off a huge, slowly decaying F-450.
Then came the point of no return. Strategic application of an electric grinder eventually got my YJ's old shock towers off the frame, and a little cleanup grinding and painting made it look like they'd never been there. This job is MUCH easier to do with the fenders removed, since there's weld on the side and top of the frame rails that needs to be ground off. I was doing this at the same time as my engine swap, so the access was excellent, as you can see in the pictures.
Lining up one tower on my frame rail, I found that the two predrilled holes were too low for me to use without the towers interfering with the "roof" of the fender, so I drilled two new 1/2" holes in each tower, each one inch above the original holes, which were spaced 2" apart. If I ever install a 1" body lift, I'll be able to remount the towers using the original holes and get an extra inch of travel.
In order to get the new towers properly positioned, I clamped them to the frame with big C-clamps and installed the shocks. Then I moved the towers as needed to get the shocks more or less vertical, and to get the new holes in the towers centered vertically on the sides of the frame rails. Then I marked and drilled out two 1/2" holes in each frame rail, clear through both sides.
The most elegant way to secure the towers would have been to drill 3/4" holes right through both walls of the frame rails and weld 2-1/2" long steel sleeves into each hole. Lacking a welder, I decided to use 2-1/4" long sleeves positioned inside the frame rails, one for each bolt. With a little creativity, it was possible to get the sleeves inside the frame rails by fishing them in through nearby holes in the sides of the frame rail. With the sleeves in place, the two bolts were installed through the tower, through the frame rail (and sleeves), and then through a small backing plate made of 1/4" c-channel. The nuts went on the other side of the backing plates. I found that factory YJ shackle bolts were ideal for this: good strong grade 8 bolts, with nice wide heads and self-locking nuts. The idea is that this setup will spread the force exerted by the shocks across both sides of the frame rails.
With the towers positioned as I've described above, the tops of the towers clear the inside of the fenders by about 1/4", which is about right in my estimation.
These towers have netted me roughly 4-5" of extra shock length. The picture on the left at the top of this page shows the old tower placed next to the new one, for comparison. Too bad the angle of the photo sucks.
Here's a couple more pictures showing the towers installed:
This really is a pretty simple upgrade, but the results are pretty profound. Those are Rancho 5012's I've got in there, the longest off-the-shelf shocks that Rancho makes, and I think the at-rest extension is pretty good. We'll see how it looks the next time I get it on a ramp, I guess! I have noticed that these towers angle the shocks out slightly more than the factory towers did. It doesn't look like there'll be any interference between them and the tires at full compression, but time will tell.
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