Frame Boxing Advice On 73 Cj5

I need some help concerning how to tie in my new box plates with the factory boxing in the front half of the frame. Looking down at the framerails you can see that the rails sort of step down and get thinner before getting to the factory box plates. Now the question is is how do I tie the plates together??

 

On mine, I went behind the existing boxing. It gives you a bit of a shelf to weld to, rather than laying the bead out on the corner. It’s sorta hard to see...

 

How far should I go back behind the existing box??

 

What’s your intended use?
I’m in the camp of “if you’re going to plate any, plate it all” because wherever you stop if partially done, the frame will flex from there back, and not flex where you plated, and cracks will develop where they meet.

Notice that the factory boxing around the engine is a much thinner material than the frame itself. I believe this was done to allow some give, rather than making that section solid. Even with the thinner material, I’ve seen cracks develop at both ends of that boxing.

 

Oops I meant like how far the new plate should go back behind the old plate? My bad haha. I am planning on boxing the whole rest of the frame since I do intend to beat on the Jeep alot

 

It doesn’t need to be much. Maybe 1/4”? 1/2”?

 

Actually, you could take it in far enough to get a stitch in the big gaps in the corners where the factory boxing ends.

 

Gotcha. Thank you for the help I really appreciate it!

 

So I need some more help. Bear with me

Looking at the middle section of the frame. (The longest section) and I was wondering if it really needed the full length of box plate? i was thinking I’d box the area around the spring hanger, continue the factory box just a little bit up front, and then add a little piece in the corner underneath the first crossmember that’s behind the spring hanger just to tie it in better. And then run a strap inbetween the two inner spring hangers on the underside of the frame and run the strap a couple inches past them.

I’m still leaving the rear half of frame fully boxed. Would I run into issues with that being fully boxed and the middle just reinforced strategically?

On one of these threads I saw that Tim said the factory baja racers were only strapped and I don’t plan on going full baja mode with it so it should hold up?

I’ve never done something this extensive before so I am still very much learning so bear with me lol


sorta like this. It’s a rough drawing haha

 

Keep in mind that the racers probably had cages incorporated into them that took a lot of the flex out of the frame. They only had to worry about the spring mounts and steering box ripping off, or the entire thing folding on a hard landing.

As a reference, I have a 13(?) point cage in my 3b that runs from frame-end to frame-end, and only the front frame horns are boxed. I’ve put more air under those tires than most people here would believe is possible in a jeep, and I don’t think I’ve ever had a single frame crack in 20+ years. As long as you think about what’s happening on the whole frame when a pressure point is applied to one spot, and how that pressure is transferred through the unit, and where one strong point meets a weaker point, you’ll start to see where the problem points could be.

Try what you think will work, and just keep an eye on it. Watch for cracks around any ends of welds; that’s where any stressors will be. If you need to go back in and re-engineer any spots, it happens.

 

That’s what I was thinking sort of trail and error. I am planning on tying the cage in at some point but using rubber or poly mounts instead of straight to the frame.

My main concern is the front third and the back third of the frame being completely boxed, while the middle is just strapped and boxed in a couple strategic areas.

My thinking is that the middle area will allow for a little bit of flex while keeping the important parts like the spring hanger and that first crossmember towards the back firmly attached

 

The best way to make this happen without incident is to make the transition smooth by fishmouthing the plates. It’ll give rigidity to the spring mounts while still allowing some flex. Here’s one I did a few years ago like that.

 

Perfect that’s exactly what I was envisioning