For the rear, first I pounded the cracks flat where they had spidered and flared and then I cut into the cracks with a thin cut off wheel to get a nice groove to weld into. After welding I hit it with a flap wheel till it was reasonably flat again.
After that, I knew I wanted to beef up the area, so I took some 3/16" plates (I could have used 1/8") and prepared to make a fish plate for the bumper tie-in points. I rummaged through the recycling and grabbed a cereal box. I picked up the trick of making templates out of poster board and transferring it to metal before cutting from watching fab shows on TV. Who says ya can't learn from television? I stuck the cardboard to the bumper with magnets and traced the outline from the back side including the holes for the bumper.
After that, I cut it out and transferred it to the steel plate. Oh, I wish I had a plasma cutter! It took forever to hog out the holes with an angle grinder. I was going to use a hole saw to cut out the middle hole for welding purposes, but I gave that up and just used a 3/4" drill bit and called it good.
I painted the back side and the frame cross member, removed the paint where I was going to weld, and then stitched it up with the 220V MIG welder. Pay attention to the plates as to side to side and front to back, cuz it is kinda easy to get them mixed up and put one on wrong, the left plate on the right or flipped around, etc.
Jeep Frame Repair: Say no to cracks
By Mike Troy
To repair the front, I cleaned up the area with a flap wheel and an angle grinder. I cut the ragged hole into a cleaner square shape and made a plate out of 1/4 wall steel...might have been 3/16th, but it was at least as thick as the old frame steel. After that, I set the new section in place and tack welded it straight and square. I used a ball peen hammer to get the frame edge down into the plate so the gap was minimal for welding. I carefully measured off the passenger side frame section to get the loaction of the welded in nut. I wanted to be able to bolt up an off-the-shelf bumper if I decide to do that, so keeping the stock mounting dimensions was important. I marked it with a center punch and drilled, checking a few times to be very sure I was where I wanted to be.
Once there, I set a nut under the plate and bolted it up with a temporary bolt to hold it centered in the new hole. I tacked the nut and removed the bolt. It all looked good so I welded it all in very solid . A bit of paint and voila, stronger than new.
A bit of paint and we are good. After I get the shackles out of the way in the rear, I will brace the crossmember where it extends beyond the frame like a wing. That area is prone to bending under stress.
Now what if the break is more serious than that? Let us look back into the archives of C4x4 at a frame repair of a CJ7 owned by Mike Cross (A Tale of Two Jeeps). CJ frames are not boxed like the YJ frame is, so they tend to flex more and fail after years of hard use. Mike had his fail on the trail and thanks to a friend's Premier Power Welder, he got off the trail and home, but the fix still needed to happen.
Mike is an excellent fabricator and he made up these cool fish plates to reinforce the weak section of frame. Mike just loves to put big holes in stuff like those plates, but besides being cool it allows him to weld the plate in the cutout areas.
In all cases, the surface should be well prepared with paint, grease, rust, etc removed for a good weld. Use a welder that is capable of penetrating the thickness of steel you are working with. One trick I have heard about is to drill a small hole at the end of each crack before welding things up as this tends to stop the crack from running on. Since this was all getting plated, this was not done.
The stress and strain of wheelin' puts a lot of force into the steel in a Jeep. Make it a regular regimen to slide under your rig and have a look at the frame in key areas such as around the steering box, spring hangers, body mounts, etc. Better to find out now before it fails on the trail.
