There is no better Jeep to turn into a garage project than a ’41-’68 flatfender. At about 10 feet long and less than 5 feet wide, these early Jeeps can fit in even the smallest one-car garage or carport, leaving just enough room to spin wrenches. They are easy to work on and aftermarket components are relatively inexpensive and accessible. Everything from new steel bodies to complete factory transmissions are available. There are only a few components you can’t find new, but these used parts can often be found for free or extremely cheap in online classifieds. Complete parts Jeeps for a few hundred dollars are not uncommon. We were lucky enough to happen upon a free rolling chassis that we decided to turn into a running and driving Jeep. Our multi-part project will cover many flatfender and general 4x4 tips and tricks that we’ve learned over the years. We’ll show detailed info and images of our frame, custom suspension, steering, body, and swapped-in drivetrain. Our project will start with the frame, which is the backbone of every older Jeep.
For the era, the original Jeep frames were very durable. The later frames feature more factory reinforcement and boxing in critical areas than the earlier frames. Unfortunately, the newest flatfender frame you can find will be nearly 50 years old. Rust, accidents, abuse, hack repairs, and modifications plague many flatfender frames. Finding a good one to start with can be a bit of a task, and most will require some welding and fabrication to bring them back to life. Throttle Down Kustoms offers new frames for those who aren’t ready to take on frame repair. Our frame had some minor rust damage, but it was still square and serviceable.
Step By Step
Before you put any time into a frame, measure crossways from corner to corner on each side to see if it is square and not diamond shaped from an accident. Check to see that the front and rear of the frame are level and that the frame is not twisted. Inspect it carefully for any major damage that will be difficult or impossible to repair.
This was some of the worst rust on our frame. Mud, salt, and water can get inside of the front portion of the factory boxed area, which causes rust to eat the frame from the inside out. It’s virtually impossible to completely seal out water and debris, so it’s best to make sure that the water and sediment has somewhere to drain out.
Our Jeep will be receiving a swapped-in engine and custom suspension, so most of the factory frame brackets were not needed. Our compact Miller Spectrum 375 X-treme plasma cutter made quick work of the offending brackets, but you could use a torch or an angle grinder in a pinch.
With the Miller plasma cutter, we can surgically remove the rivet heads holding the brackets to the frame. This saves time and allows the brackets to be reused if need be. Grinding and torching can sometimes damage the bracket.
The flatfender leaf-spring mounts are both welded and riveted to the frame. Be careful when cutting these off. If yours are damaged and need to be replaced, you can source almost every factory flatfender suspension and engine bracket from Omix-Ada.
Look everywhere for cracks in the frame. You’ll most likely find them around crossmembers and suspension brackets like this. Mark all of the cracks with a paint or Sharpie pen so they can be properly repaired.
Inspect the frame for any missing or loose rivets. Remove the loose rivets and fill the holes with fine-thread Grade 5 or Grade 8 bolts and locking nuts with washers.
After removing the welded- and bolted-on tow hitch from the rear bumper area of our frame, we were left with this rusty mess. We used a 41⁄2-inch angle grinder to clean it up.
We fabricated a 3⁄16-inch-steel plate to reinforce and rebuild our rusted-out hitch area. Be sure to grind out all of the old paint and grime before trying to weld in new metal.
Any cracks that you find should be ground out with a grinder or die grinder. This allows for full weld penetration. It’s also a good idea to drill a small hole at the end of the crack prior to welding and grinding the area smooth. This will stop the crack from spreading.
Filling unnecessary and excessive boltholes with a welder can be a lot easier if you clamp a chunk of aluminum or brass to the backside of the hole you are working on. This helps dissipate heat more quickly so you can fill the hole without actually burning it bigger.
We like to box the entire flattie frame for increased strength and durability. You can make this job a lot easier by first making cardboard templates. They should fit inside the frame for strength. They can be then be traced to steel plate and cut out. Anything more than 10- to 11-gauge steel is a little excessive. Adding holes with reinforcement dimples is more work, but it also allows the use of thinner material to get the same rigidity. Dimple-die holes allow convenient access to the inside of the frame, too.
We decided it was well worth the couple hundred bucks to have the entire frame sandblasted. This saved us from spending a lot of time behind the grinder with a sanding wheel. It gives you a clean solid surface to weld to.
We marked the rusty spots that needed to be cut out. Consider using shapes and sizes that are easy to fill rather than random shapes.
We used our Miller Spectrum 375 X-treme plasma cutter to remove the rust hole. Make sure you get into the non-rusted thicker material where you can throw down a solid weld. Once the cancer hole is cut out, you can clean it up with a grinder. Measure for a replacement piece that fits tightly.
We use a Harbor Freight Multipurpose Magnet Holder to locate the replacement piece. Tack weld all four corners of the replacement piece, remove the magnet, and fully weld the entire perimeter.
Once the repaired area cools, you can grind it smooth and then hit it with a fine grit sanding wheel. We also drilled out the broken bolt pictured and were able to save the threads in the frame.
Our frame had the factory boxing around the engine area. It’s very thin sheet steel, so we covered it with 10-gauge steel plate and stitch welded it in place. This provides a more solid mounting point for our aftermarket motor mounts. When overlapping reinforcement plates, create a V-notched or fish-mouthed end as pictured. This helps prevent cracks in the area. Since we are using a short engine, we decided to retain the large factory tubular front crossmember.
When boxing the frame, it’s best not to fully weld the entire length. Welding only small sections is perfectly acceptable, and preferred. If a crack does start, it won’t continue on down the weld. We weld 1.5-inch sections with about 3-4 inches in between. Sometimes you have to alter the frequency to compensate for crossmembers. Stagger the welds on the opposite side of the boxing plate for the most strength and rigidity.
The flatfender front frame horns are critical. Inspect them for cracks and bends very carefully. This area almost always has damage from rust, an accident, a dropped tow bar, or butch fabrication. We were lucky and only needed to box the frame horns and fix a few cracks. Extreme damage may call for the frame horns to be removed and replaced with rectangular tube.
In the next instalment of our Garage Project GPW, we’ll attack the suspension. Here’s a sneak peek of what we are up to.