By: Ron Hollatz
Recently I got the chance to try another new product developed by Curt Hildebrand and marketed by Tera Manufacturing. Ive been running a set of Curts Revolver Shackles for the past couple of years on Project Money Pit with great success. The added suspension travel really helps me get through rocky terrain. The new products, Z-Boxes, were designed to complement Revolver Shackles by reducing the stress on leaf springs by allowing them to pivot away from the frame. Besides increasing the travel of the springs, the reduced stress will also extend the life of the springs. The Z-Boxes are available for both the front and rear of Jeep YJs equipped with Revolver Shackles. I was only able to use a set for the rear of my YJ, because I have a shackle reversal in the front. While the Revolver shackles are an easy bolt-on project, the Z-Boxes require modifications that can not be reversed.
Since the old spring hangers need to be removed, the first step is to make accurate measurements of where the springs are located in relation to the frame. In order to maintain proper suspension geometry, these measurements are critical. We measured from the shackle mount to the center of the spring hanger and marked the position on the frame. This needs to be done on both sides of the Jeep. Now that we knew where the Z-Boxes needed to go, we were ready to begin.
|Lowering the axle to disconnect the rear springs||Meauring for the correct mounting position||Minor trimming of the body mounts was required|
The installation starts off easy enough. We lifted the rear of my YJ with a fork-lift to get it high enough in the air to remove the rear springs from their hangers. The springs were then unbolted and lowered out of the way. It was then time to remove the old spring hangers. This is the point of no return. Once the spring hangers are removed, there is no going back. We used a torch to cut the old hangers off, being careful not to weaken the frame by heating it up too much. An angle grinder was then used to clean up the frame and provide a smooth mounting surface for the Z-Boxes. The upper portion of the Z-Boxes consists of a channel that fits over the frame. One of the body mounts on each side needed to be trimmed to allow the Z-Boxes to slide onto the frame. This was easily done with the angle grinder.
Now we were ready to mount the Z-Boxes. Since our measurements were based on the center of the spring bolt, we bolted the springs to the Z-Boxes first. Then, using a floor-jack, we positioned the Z-Boxes using the marks we made on the frame. The Z-Boxes are designed to be mounted using a pair of 7/16" bolts through the frame. Unfortunately, we neglected to make sure the drill was in the shop before we started the install. Our solution was to stitch weld the Z-Boxes to the frame. This was done slowly to avoid and damage to the frame by overheating it. All that was left to do now was to apply a good coat of paint to avoid rust.
With the rear of the Jeep still in the air, it was easy to see how the Z-Boxes work. With the Revolver Shackles unfolded, the springs were still flat due to the Z-boxes. It also became apparent that a limiting strap would be required to keep my drive-shaft from binding when the rear axle dropped. Under normal use this shouldn't be a problem since only one wheel would drop at a time.
|Testfitting the Z-Box||We chose to weld the Z-Boxes instead of bolting them on||Mounted and ready to flex|
The first real test of the Z-Boxes came at the Easter Jeep Safari in Moab. Right away I noticed my YJ felt smoother crawling over rocks. The Z-Boxes worked as designed to reduce the stress on the leaf springs and allowed the suspension to travel with less bind than before. Of course I did not follow my own advice of putting a limiting strap on the rear axle. On a loose bumpy section of trail I gave it a bit too much gas causing the rear end to bounce over some rocks and bind the drive-shaft. Luckily all that was damaged was the pinion yoke. The only complaint I have about the Z-Boxes is they can be noisy on bumpy sections of trail. I spoke with Curt Hildebrand about this, and he recommended having one of the plates sprayed with Rhino Lining as a cushion. The Z-Boxes I have were from the first production run at Teraflex, and I've been told the noise issue has been addressed.
When I first saw the design of the Z-Boxes, I was concerned with how they might react to side hills. After trying them out in Moab, I've decided my YJ didn't feel any different than it did without the Z-Boxes. The same can be said for performance on the street. While my Jeep doesn't get driven much on the road, I haven't felt any negative handling as a result of the Z-Boxes. I'm sure this is helped by the upper wishbone installed on my rear suspension to reduce spring hop and limit side-to-side movement of the rear axle. Due to the amount of lift and suspension modifications on my Jeep, I don't drive it like a race car anyway. Overall, I feel the Z-Boxes work well with my suspension setup.