Lets talk about the unibody

Well I've been thinking more and more about the unibody lately especially after snapping a welded nut off inside it trying to get the leaf springs off. But it's just been bothering me since it's the one downfall of the xj and lately it seems to me overly complicated/stupid after staring at it all the time while doing this rear axle swap and being a pain in the ass to get the bolts out of the leaf spring mounts. So I've been thinking of what I'll be doing for frame stiffening and such in the future along what to do about this broken off nut, any ideas? I'm getting to it by the hole in the end of the frame rail in the rear and i'm planning to make better leaf springs mounts just not sure how yet. Also I was wanting to see any tricks and upgrades anybodies done to theirs to fix or simplify some stuff involved with it. I've seen plenty of frame stiffening and stuff which I'd like to do but I think it would be overkill/(I got other things to upgrade) being a light wheeler on 31s eventually going to 33s or 35s. But I would like to eventually add in solid cross members at the front rear middle and a couple other areas since I will being working on those areas anyway (bumpers, skidplate, etc.) So what do you think about the unibody and such pros and cons. I like the unibody overall for being simple and as one with the body like a chassis but the strength and complicated areas are the downfalls. I'm hopin for some good things so i can stop being so self conscience about it lol.

Actually, it's "uni-frame" construction since it has full length frame members, even though they're sheet metal. Unibody has subframes bolted on front and rear .

i've seen people plate/ reinforce the area in front, right behind the bumper. a good solid belly pan might add some extra rigidity.

makes curb weight light. (was just comparing to tacos and 4runners and the've got 500# plus on us)

makes headaches when bolts strip out, when stuff bends due to light wieght "frame"rail

makes for fun arguments with dumb people about body lifts. (like one of my old neighbors lol)

makes for less bolts, and less parts. (which i am a fan of)

If you plan on wheeling for the next few years, frame stiffeners from from to rear are not overkill.

cruiser54 said:

Actually, it's "uni-frame" construction since it has full length frame members, even though they're sheet metal. Unibody has subframes bolted on front and rear .

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No, that's not correct.

Original Poster should look around the site a bit, and also search the web. Many threads on the subject of sub-frame reinforcement.
Also, I find nothing "Stupid" about the design; IMO, the XJ has one of the better built chassis you will find.

Some threads you may consider looking at:

http://www.naxja.org/forum/showthread.php?t=6443

http://1997jeepcherokee.blogspot.com/2007/01/frame-stiffeners.html

http://jeepinoutfitters.com/scripts/prodView.asp?idproduct=562

Zuki-Ron said:

Also, I find nothing "Stupid" about the design; IMO, the XJ has one of the better built chassis you will find.

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I agree with you on the design portion, but for a good end product it has to also be built well. This is where IMO Chrysler dropped the ball. More specificlly I'm talking about the welds on the sheetmetal. Most of the flat welds that I've seen are either undercut or too hot (LCA brackets for example). Also there seems to be a lack of spot welds at the seams, as well as a completely lazy use of seam sealer (if at all).

Sure I might be a little Biased, but I have been much more impressed with the Imports that I've worked on. Honda for example has a spot weld on their seams about every 1.5". On the XJ your lucky to see a weld within 4". Chrysler just seemed to halfass the assembly of their product.

On the flip side, I think the XJ is an excellent chassis to work off of and can be one of the best out there if done properly. I wouldn't own one if I didn't think this. :lickout:

Zuki-Ron said:

No, that's not correct.

Original Poster should look around the site a bit, and also search the web. Many threads on the subject of sub-frame reinforcement.
Also, I find nothing "Stupid" about the design; IMO, the XJ has one of the better built chassis you will find.

Some threads you may consider looking at:

http://www.naxja.org/forum/showthread.php?t=6443

http://1997jeepcherokee.blogspot.com/2007/01/frame-stiffeners.html

http://jeepinoutfitters.com/scripts/prodView.asp?idproduct=562

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That's what Jeep called it when they introduced the XJ. As service manager at the local Jeep dealership, we had to watch films at the time of introduction showing the assembly line with the robotic spot welders sticking the "uni-frame" together. They made quite a big deal of it.

I'm not saying it couldn't be improved upon for some of the uses an XJ sees today. I'm sure it could. It was great for what it was originally designed for.

Interesting...

However, my point was that what he is specifically calling "unibody" is what GM used on the NOVA etc.

The fact of the matter is that the XJ frame is of monocoque design where the complete body is structural frame. This is also refered to as "Uni-Body", Uni-Frame", or "Unit-Frame" construction.

GM used a hybrid monocoque design on the NOVA and many others, not quite a true "uni-body" or "uni-frame" construction because they bolted complete front and rear frame sections to the body with isolators. I suspect they did this to absorb road noise, and for ease of assembly.

Monocoque construction is not new. Ford, GM, and Chrysler used it on a number of small and mid sized cars, and vans. The XJ body was designed by Renault. That's right, the same folks who brought us the "LeCar"

I understand. That's why I said the Jeep is uni-frame, not uni-body, like GM cars.

there quite a few products for stiffening of the XJ

tnt customs

HD offroad engineering

temper mental racing

etc.

HD offroad engineering

The only one worth mentioning. Brian is a good guy, his parts fit well and he is a long time member and supporter of the club.

http://www.hdoffroadengineering.com/

Yea that all makes a lot of sense. I totally agree with boostwerks that the unibody (frame) design is good and simple in concept, all it needs is just some support and maybe some mount reconfiguring. I like to think of tube buggy frames being unibodys lol where everything is solid attached. Heres one I like a lot. Oh and did I say stupid? I take that back.

Super mud said:

Yea that all makes a lot of sense. I totally agree with boostwerks that the unibody (frame) design is good and simple in concept, all it needs is just some support and maybe some mount reconfiguring. I like to think of tube buggy frames being unibodys lol where everything is solid attached. Heres one I like a lot. Oh and did I say stupid? I take that back.

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It's funny you mention that because I've also thought that this rig is the best example of good reinforcement without the use of an interior cage. The stiffeners extend from the rear to the front and cover not only the sides of the uniframe but the underside as well. Combined with good stiff crossmembers (front, middle and rear) the chassis will be strong as nails and last a very long time.

Yes, it was and is an excellent design. I don't think the original engineers ever conceived what we would be doing with these rigs after they became plentiful and cheap.