To weld or not to weld

I'm building a new Jeep from the frame up. It's actually the 3rd frameup except this time I'm starting with a new frame and tub. Actually I just told my wife that I was going to change out 2 parts. The tub and the frame. I got a M38 frame and I've removed all the brackets and mounts (except the machine gun mount heh, heh)and had it sandblasted. I'm going to true it up, although it looks really straight, and weld on a new rear X member/ bumper to replace the original stamped metal one. It will be made from 3/16" 2" x 4" rect. tubing. The front bumper will be made from the same material. My goal is to make this frame rigid. It will be fully boxed. My question is on the front bumper. My questions is, should I weld the front bumper to the frame or bolt it. It seems that welding it would help accomplish getting the rigidity I'm looking for, or would I just be creating a stress point at the welds that will eventually crack. Sorry for being so long winded.

 

Why do you want a rigid frame? Seems every rockcrawler in the world wants more flex not less. I'm sincerely curious.

Henry Ford made the Model T deliberately flexible, and they will go darn near anywhere a Jeep will, and some places a Jeep can't. Fifteen million of them also proved the point that they don't break.

I heard that more recent frames also were riveted, not welded, to avoid creating stress risers. If you really need a rigid frame, maybe you can build a structural roll cage.

Good luck.

Pete

 

I understand what you're saying PeteL, but I don't really agree. Those old Jeep bodies aren't insulated very well where they are bolted to the frame, so when the frame flexes, it stresses the sheetmetal too. Let the suspension do it's job.

 

I agree with Pete. These old JEEP frames where ment to flex. I understand some people don't want them to. But IMHO I would bolt it on.

 

On a jeep that is mainly street driven with some trail duty it prob. will never be a problem. But on a trail only jeep that all it ever does is flex and get beat on it will eventually crack or break. Imagine bending a piece of metal with your hands over and over its going to get weak and break after a while.

If your going to have another x member close to the bumpers like the factory set-up I'd just bolt them on, if not weld 'em.

 

The less bolt-ons the better.

I completely redid my 5 last winter cause the body and frame and driveline were all doing their own thing, it was way outta hand. A couple of years of rockcrawling with 38's trashed the frame. I disassembled the frame-all I had were the two stamped c rails. Cut out the factory boxing at the motor and boxed it front to rear with 3/16. Front winch mount/crossmember, motor mounts/crossmember, tranny mount/crossmember, and rear bumper all welded in. Steering box mount welded on.

When I boxed the frame rails, I made no attempt to controll the warping, because preventing it would have been more work than dealing with it afterwords. Welded all 11 feet down and back and they bowed about 3" in the middle and twisted and...stuff.

It made a HUGE difference in how my 5 feels in the rocks. I have a better sence of when and how bad things are binding up. Don't have to reweld the cracks after every trip (rear hanger of front springs were the worst).

Definately worth all the work.

 

Nice engine mount, CAP. Looks like you have an M38 frame also. Here's the "why" behind my plan. I have no less than 10 weld repairs on my frame. As was mentioned above when the frame flexes, so does the body. Add a little rust at the body mounts and a lot of flex and you get absolutely no support for the frame from the body. My Jeep is 80% trail use. It's flexed out. I have a very soft 4" spring lift with a shackle rev. and it rides like a Cadillac. Well, kinda. Anyway, I'm leaning towards the concept that the suspension should be doing the flexing, not so much the frame. Early Broncos had fully boxed frames and I see alot of them out on the trails here. Difficult trails. Anyway, there is a lot of great ideas to be had on this forum and I'll be posting pics as I get going. It's going to be a long build, but hopefully this will be the last. I plan to finish the frame this winter, set the new tub on and test fit my engine, tranny and T case for the crossmember and engine mounts. Then put it all back in ol Posi and wheel the summer in it. Get the new tub painted, then next winter do the whole enchilada swap-over.

 

Throw the frame away and build one from scratch. It will save you time. ---____--- That is all a frame for a Willys needs to be, made from 2X4 3/16 min. Search on Pirate 4x4 after you purchase a star or use google and pirate4x4.com in the search. There is even a topic of the month on frame building. You can also buy a Matkins or Advanced Frame works frame, but they are big money.

Otherwise weld the bumpers in and FULLy box the frame. Tie the roll cage right through the body into the frame for support. Below is why my frame got sold for next to nothing.
View attachment 15304
While you are at it, lengthen the wheelbase and use YJ springs.

Here is somone elses ideas
http://www.film.queensu.ca/CJ3B/Tech/Frame.html

 

Have any idea how much a frame made from 3/16" 2" x 4" tubing would weigh? The 4' piece i bought for the rear bumper probably weighs 30+ lbs. Matkins doesn't make frames for pre '72 CJ's, but at about $3k a pop for one of theirs, I really don't care. Be carefull how much time you spend on the Pirates site. Before you know it your hat will be on backwards. By the way, that's a great link you posted.

 

Well I can not lift mine, but can move it around by myself and flip it over, etc. Will it break is the better question? I sure hope not.

Haha The only time I ever wear a hat, other than a beanie for warmth, is when welding, and it happens to be a pirate hat that is designed to be worn backwards.

Pirate has some of the most knowledgable offroaders around. I have learned so much searching on that board, but rarely post. When I do it is to help people.

 

I used a different approach. ....Both.

After repairing the frame horns and welding in new shackle mounts, boxed the frame back about a foot or back to the motor mounts. I welded in a (angle) reinforced plate across the frame ends. The plate also serves as my winch mount. This stiffed up the front end. You would be surprised at how much a saginaw can flex the single frame end when running 33's. The bumper was bolt on as it should be.

 

Truckhaven? Isn't there a Truckhaven Trail? It sounds familiar...

Just so that I'm on-topic, steel doesn't have to fatigue when it flexes. Whether constant trail use exceeds the dynamic limit, I don't know. However, we've been through this topic a lot - seems that you either have to go flexy frame (original frame with minimal added steel) or stiff frame and flexy suspension. Not much middle ground.

 

I believe Truckhaven is in So. Cal.

 

I would go flexy suspension. You can adjust how soft or stiff you want your suspension with shocks and springs. The frame is going to flex however much it wants and won't be adjustable. When the frame is flexing it is also stressing the motor mounts, trans mount and body mounts. I vote stiff frame.