TOTM: Unibody Improvements

[rstrucks]

Frames, we don't need no stinking frames! Well, they'd be nice to have but we don't need them.

Bracing, plating, reinforcing, cage tie ins, etc..... What helps your unibody live a longer life? Let's hold off on the full on "tubed out" tech as we will cover that topic before too long.

[JohnBoulderCO]

WJ's are stiffer to start off with then a ZJ.

Adding Clayton's long arm kit gives you a "sub-frame" which helps a bit.

[OverkillZJ]

Claytons subframe helps, so do bumpers and sliders - but my belief is that unless you build some kind of structural cage to keep it square, eventually it will turn into a tin can. The only reason I buggied my first ZJ, is it was driving crooked, the doors were inches from lining up, and there was just no way to repair the damage. Cutting it up, we found cracks in almost every structural "corner" of the unibody.

[moparrr07]

the wj unibody was designed and then further redesigned by porsche who said when they were done with it, it was equal to a full frame strength,

theres always room for improvment, unibody or full frame

[slim616]

The only way I've found out to improve it, is to start with something with a frame

But to be honest between the cage which was tied into a sleeved rail ive had no issues with the unibody other then typical b.s. of having to use/tie into it. Prior to that my unibody used to flex so much that non of my doors worked.

[chadjans]

and then further redesigned by porsche
who said when they were done with it, it was equal to a full frame strength,

What are your sources for this info?

[moparrr07]

What are your sources for this info?

i saw it on wikipeida and i didnt believe it, so i searched, i found it stated on a couple sites but this one seems to have the most info....

cool reading

http://findarticles.com/p/articles/m...20846019/pg_2/

[moparrr07]

i mean just because something has a "full frame" doesnt mean its all that great, ever flex out an late 80s ranger? full frame and i can guarantee it twist way more than a stock zj

like i said there is alway room for improvment

[blackbeer]

Seems like as good a place as any to bring up the TNT frame sleeves vs claytons sub frame...
Off the bat claytons go under the uni and are thicker material where as TNT sleeve the outer side and bottom but are thinner.
I've heard support for both in my opinion I like the TNT design for welding sliders/boatsides or cage tie in going all the way up the uni is nice. I don't think claytons can be much stronger? Thoughts? Corrections or comments. I've seen some amazing home mad jobs done but none that make extra sets.. Takers?

[Steel City ZJ]

Seems like as good a place as any to bring up the TNT frame sleeves vs claytons sub frame...
Off the bat claytons go under the uni and are thicker material where as TNT sleeve the outer side and bottom but are thinner.
I've heard support for both in my opinion I like the TNT design for welding sliders/boatsides or cage tie in going all the way up the uni is nice. I don't think claytons can be much stronger? Thoughts? Corrections or comments. I've seen some amazing home mad jobs done but none that make extra sets.. Takers?

I posed this question not to long ago to some friends and it was never really answered. I just ordered the Clayton rear LA upgrade which comes with the stiffeners so I'm interested to see if I notice a change

[AgitatedPancake]

I really like the TnT stiffeners. They offer extra clearance under the frame rails where claytons sticks down, and go further front to back to offer protection. I plasma'd out some evenly spaced holes in Andy's TnT stiffeners so I could weld it to the unibody with some nice even weld spacing, it should have a hard time removing itself haha!



In this one you can see out of the entire TnT suspension, pretty much none of it rests directly below the frame rails like Claytons, where he has LCA mounts underneath the frame rail. This design saves you a few inches of clearance where it's important. On my WJ I've hammered the ever living piss out of all my LCA mounts and the Claytons subframe connectors

[SirFuego]

This is a relevant post Maxx made about Elliott's thread mentioning an FEA that Kraqa did regarding frame stiffeners.

found it on elliott's build over on nc4x4

All ZJ's/XJ's/WJ's/KJ's are unibody, meaning the frame and body are in itself one piece. It is a cheaper way of mass producing vehicles which is all Daimler Chrysler cares about. Trying to design suspension around this can be very tricky but thanks the the popularity of the 4x4 sport almost every approach has been conceived and executed. Manipulating the unibody is inevitable when building one of the afformentioned rigs into a capable crawler. For all information on welding related to the unibody, please take a moment to read the Unibody Welding Bible. Thanks to a good friend of mine Kris Fraser for the comprehensive research on unibody strengths and how to modify them.


Option A: Sleeve the frame rail with chopped 4x4 3/16". Plug weld throughout. This is pretty easy to do with the correct tools. This is pictured below. Graphically shown: Green area being the ZJ frame and the orange part being new sleeve.



Option B: Weld a smaller size SUBFRAME onto bottom of existing unibody. This is what the Clayton kit uses. Links are not as easily mountable to this type of setup and you lose approx 1" of clearance at the frame. Also a pic is shown below.




The plate on the ends are used for the analasys. The force to the frame rail is applied to the 2" portion sticking off the right side. The frame rail is anchored and the opposing end from where the force is applied. The force is 1000LB. This is the deformed DIY Sleeve (option 1).


And here is the subframe (option 2).


If you look at the numbers to the right of the framerails you can see that the subframe actually moves less. This was surprising to me. These aren't exactly the same forces applied while wheeling but it gives you an idea of its strength. Tests on torsional rigidity would need to be run to get a more comprehensive analysis of its true strength. (Thanks to Kris for crunching the numbers on software I can't afford. )

I know this is probably boring for 99% of the readers on here but this kind of stuff really fascinates me and I'm sure someone will have a good appreciation for it. I will update this thread tomorrow as more work is getting done.

[rstrucks]

I'll try to post some pics later of the small amount of unibody plating/bracing that I have done. For now I will say that I have not had the issues many others seem to have. I have never not had a door shut or line up and the body of my ZJ does not feel tired or worn out or make too many noises when wheeling. Granted, I don't wheel mine as much or as hard as others but I do wheel it. Adding the cage last year and tying everything together has helped keep the unibody feeling solid.

For the most part I think the biggest advantage to having a true frame is having a strong and convenient place to add mounts and brackets. Just because you have a frame doesn't mean that you don't have to worry about stress cracks and fatigue either.

[SirFuego]

I know that bumpers were a previous TOTM, but I'm posting it here, because I seriously think that if done properly, a bumper could also help to strengthen the unibody.

When you are working with the bumpers, you are able to sleeve inside of the frame. I think this is important because it makes the bumper mount much stronger and also less prone to getting stress cracks in the unibody. My primary motivation for thinking that this really helps is that despite the abuse my ZJ has been subjected to, the unibody around the bumpers hasn't cracked yet despite this internal sleeving being the only real reinforcement that has been done to the front and rear of my rig (in reference to the pre-roll cage stage of my rig -- my rear "bumper" is now just a piece of 2x4 welded to the rear unibody channels due to the dovetail/bob and the cage obviously strengthens everything, but I won't get into that since that's not the focus), but the bumper I posted here is living on in O'Tools new 5.9 ZJ.

Of course this method of internal sleeving is really only possible for the bumpers, so this isn't going to replace any of the other plating/subframe ideas already mentioned.

Front
In the front, if you want a very tight fit of the internal sleeve, you will need to cut out the front crossmember. An air chisel is your friend to get remove the stock nut serts.


With a little grinding an notching of the steel tube, you can get a 5x2 to fit snugly.




Once you get the bumper designed the way you want it (my front bumper is intentionally very simple-looking, but there is no reason you can't just use the same concepts for a more aesthetic bumper), you can drill some holes and weld in some nuts in the internal sleeve. The way my buddy designed the bumper, the entire thing is actually one single piece -- including the internal sleeves. It's such a tight fit that he needed a sledgehammer to get it in. He joked that it's in there so tight that I could probably winch without bolting it in -- and to get it off, I'd probably need to remove the bolts, hook the bumper to a tree and floor it in reverse a few times to get it out. And of course he went overkill with grade 8 bolts:


Rear
A similar idea for the rear was developed that was actually a hybrid of the way ZJ and XJ rear mounts. A 2x4 was sleeved and notched (around the gas filler tube) into the rear frame rail and mounted using the "ZJ" style mounts that the trailer hitch uses. He then welded some angle iron at the end of the sleeve, drilled some holes, and made some nut plates to mount it "XJ style:

[downtowncb]

Hell on a ZJ even the tow hitch is structurally integral. I was rearended in the Polar Bear about a month ago, I took off the tow hitch and gas tank skid to get the damaged bumper out and start designing a steel bumper. In the mean time I'm driving around without a rear bumper or tow hitch and if I park on the SLIGHTEST of hills the tailgate won't close properly. I'm suprised how bad it actually is, it's pretty pathetic.

For the sake of sharing my frame plating again. I plated from the cab forward on the outside and from the cab to the motor mounts on the inside in .125" plate.

[Kauzi Zj]

So, Im not looking for facts and technical data, but how many of you think this is a necessity for a DD/Expedition Trail/part time Crawler, thats only going to be mildly modified(compared to some of you on here)?

[OverkillZJ]

My ZJ on 6" lift, long arms, rocker protection, stiff bumpers, etc - was essentially wheeled like an expedition rig. And eventually I had to cut it up because it was so tweaked it was no longer square. Given that as with 3-5 years of wheeling on it, but it's not like I was always crawling rock gardens or jumping the rig. The unibody just gave up the fight. I intend to brace the hell out of the 5.9 to prevent that from happening, it still has doors that line up!

[Kauzi Zj]

Well, I won a set from Moonworks, so once I get them, I will get them installed. I just wasnt sure ho "needed" they are.

[SB406]

I think the key is to add strength BEFORE it gets all screwed up. If you wait until it's rotted out or smashed, you are doing a repair, not adding strength. Remeber, shapes add strength, but smashed is not a shape.

We had to add a lot of metal to Jared's ZJ in order to fix the weakened floor structure, and add additional strength for repeat abuse (cage).
Remember, cars like ZJ's were designed with the intention to take 1 really good hit, and fold up. As long as the occupants walked away, it was a success. In the wheeling world, we expect our vehicles to take multiple really good hits, drive out of it, and run the obstacle again.

[Jeeptech01]

Subscribing for when I have a spare min or two.

[chadjans]

So, Im not looking for facts and technical data, but how many of you think this is a necessity for a DD/Expedition Trail/part time Crawler, thats only going to be mildly modified(compared to some of you on here)?

This made me laugh.

Doesn't the already been posted "facts and techincal data" show that frame rail plating is a "necessity?"

[FearTheDentist]

Doesn't the already been posted "facts and techincal data" show that frame rail plating is a "necessity?"

I don't have anything like the technical\fabricating background to have an "informed opinion" on this, but I do have an observation. From what I've seen the majority of unibody rigs wheeled in the manner Kauzi is describing have no unibody plating with the posible exception of the frame rail stiffener in a Clayton's kit. I haven't seen many such rigs develop issues resulting from over-stressing the unibody- this seems to be reserved primarily for boneheads like myself who beat the snot out of their rigs. Matt's experience above may suggest otherwise, but I suspect his rig saw a lot more use than is typical, and I doubt he took the bypasses very often. SO- maybe from a "purist" point of view plating is necessary for all unibody rigs in this application, by my practical experiece says that it's hardly neccesary for the average Joe.

On a seperate note- A concern I've always had with unibody plating is that by plating in one area, aren't we creating a stress concentrator in another? It seems like you would be focusing the stresses on smaller sections of the unibody, and thus could actually increase the chance of a failure. I think my reasoning is flawed, as this obviously isn't a problem in the real world, but I'm curious what your thoughts on this are.

[chadjans]

Plating is moving around the weak points. With that being said, plating ZJ is a necessity. The control arm mounts tear off, the rear near the gas tank cracks, the areas around the motor mounts cracks and the steering box area tears around the bolt holes. The areas around the middle are the strongest because of the structure around it. The areas at the peripheries are the weakest and MUST be addressed.

I have seen all these issues first hand either with some on my rig or Kevin’s and others. I have yet to see any issues with a WJ, I guess because Porsche has touched the engineering. Although I do know HalfDoc’s and Justin’s doors are starting to change characteristics in opening and closing.

A systems approach is the best way to address the issues. Which is why I beleive the Clayton's kit has been successful. But a cage with tie ins and some sort of frame rail stiffener and plating at the ends will tighten up the characteristics of the rig substantially.

[AgitatedPancake]

My WJ has held up pretty damn well with Claytons. I've had to rebend the top of my doors a couple of times to make them follow the body lines again, but never had issues opening or closing them. I also have the forward most part of both frame rails plated on the inside, supporting the power steering box and other main structures.

I will tell you where I have some flexing that has become a pretty serious issue. The rear frame rails, at the frame side sway bar brackets. Back when I had a 4" lift I had an upgraded swaybar, well over time the frame rails cracked at the mounts for the sway bar brackets. I removed the sway bar and didn't really worry about it, until this last year. I took a couple massive hits on my rear bumper in which the frame rails flexed up to the point where it slightly bent the floor, and the top of my bumper hit my hatch and actually cracked a tail light. It sprung back to the normal position, but to do that damage the bumper had to move 2"+ vertically up into the hatch, and it's definately not the bumper itself doing the moving, the frame rails are hinging at the cracked point. I hope to have them plated before KOH

[squashman702]

And of course he went overkill with grade 8 bolts:

Not to nitpick, but the rearmost bolt won't do much . . . supposed to be 3*(bolt's diameter) worth of material between the hole for it and the edge according to what I've read. Highly unlikely that the bumper would go anywhere with the other bolts holding it in, however.

What did you do to strengthen the steering box portion of the unibody? Did you tie it into the bumper at all? We just build a bumper for my buddy's XJ, and plated the outer unibody rail and tied it all in with the steering box bolts, which is why I ask.