"Frame" stiffeners

Everyone knows that the unibody of the cherokee is a weak link. They are made of thin material and will crack and bend with stress. Some people have thrashed on them to the point of having a permanent sag to their whole xj chassis. Think of it like a wet piece of cardboard that sags in the middle when supported only at two ends. Eventually it will fold right in half. Well, I have plans to build a radius style long arm front suspension that will be based off the crossmember and I wanted a sturdier platform to mount my new crossmember to. I also like the added rigity to keep down the creaks and groans of the unibody.

I made my frame rails from 3x3x3/16" material. It is important to remember that when welding your reinforcements to the unibody that you keep down the heat buildup. The best way to do this is to "stitch weld" the metal to the unibody. I did mine with approximately 1-2 inches of weld leaving 3-4 inches between welds. I also cut holes in the stiffeners to distribute the load from the crossmember and suspension more evenly. Most people just drill some half inch holes and do rosette welds. I have heard this works just as well and serves the same purpose. Many guys will also tell you to not do a full length weld along the rails because it will act as a track for a developing crack to follow. I don't have first hand experience with this, but I figure that the stitch welding is plenty of weld surface to hold everything in place. Below are a few pictures of what I did.Here is my angle iron before I cut the holes and welded it in.

You will have to make two cuts (notches) in the angle to facilitate the bends of the unibody. My reinforcements only run from the rear suspension mounts to the front lower control arm mount, but I have seen many people run them the full length of the undibody frame rails all the way from the rear bumper to the steering box mount. If I had the whole thing stripped down to that point I think it would be a much better modification. This will have to do for me though.

Here are a few pictures of the finished product. As you can see from the pictures I also welded two nuts under the angle on each side in addition to the threaded inserts already in place in the stock unibody. These extra bolts will be used for attaching the new crossmember and suspension mounts.