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  #1  
Old January 16th, 2009, 20:38
themangeraaad themangeraaad is offline
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XJ Unibody rebuild

So I have trimmed my rear fenders as far as I can and probably a bit more than I should have (well without doing some extra welding.. which I didnt do. nuts/bolts all the way ). I knew this could potentially cause issues down the line, but for the time and all it was fine.

Now the XJ isnt the DD, so I am thinking about what to do next. Can anyone tell me how thick the unibody is? I know its probably out there somewhere, but I couldn't find it with a few searches and I am getting tired, got a long day ahead of me tomorrow w/ packing the Uhaul and driving all night tomorrow night, and just want to pass out.

What I am thinking is replacing the unibody frame rails with slightly thicker material, but something with the same dimensions, and making it be full boxed... aka making it more of a frame. Then I could either weld the body back onto this "frame" or I could add some structural support to the body and bolt it on (so it would essentially be a frame). I would probably be doing the floor pans as well since they are rusted out a bit (have makeshift patches in for now which are doing well... but might as well do it right).

Anyone got any advice on this? Good/bad idea? I love my XJ and I just dont want to run into a position where something gives out because the unibody is f**ked, and I figure if I could spend the time making frame stiffeners why not just go all out and redo everything?
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  #2  
Old January 16th, 2009, 21:08
delaminator delaminator is offline
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Re: XJ Unibody rebuild

just go all out and do it then, why are you looking for approval from fellow board members, just do it, document it and have a unique XJ?
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  #3  
Old January 16th, 2009, 21:30
themangeraaad themangeraaad is offline
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Re: XJ Unibody rebuild

Not really looking for approval... More looking for a heads up incase anyone looked into this before and ran into issues that they could pass on before I do something that will lead to my XJ being in a junkyard or becoming a parts rig. And also looking for how thick the walls of the unibody are since my XJ is 400 miles away right now and I cant make any measurements Trying to find out what size I should use to improve strength a reasonable amount, figured stock size would be a good starting point.

So not approval... more along the lines of advice
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  #4  
Old January 16th, 2009, 22:44
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ehall ehall is offline
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Re: XJ Unibody rebuild

somebody posted up pics where they bolted the XJ on top of some other frame, don't remember which it was though.

anyhoo if I was going to go all crazy like that, I'd just cut the damn unirails off and bolt the floorboard to a real frame
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  #5  
Old January 16th, 2009, 23:32
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ZacSquatch ZacSquatch is offline
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Re: XJ Unibody rebuild

Check out advanced fab and see how guys are rebuilding and beefing up their unibodies...

If I were you, i'd just beef up the rails as is, buy or make some stiffners, and box whatever else you can/want/deem nessicary with angle iron or cut open box tube...

Do research this please, it can prove most life saving.
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  #6  
Old January 17th, 2009, 00:25
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emr1101 emr1101 is offline
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Re: XJ Unibody rebuild

Quote:
Originally Posted by themangeraaad View Post
So I have trimmed my rear fenders as far as I can and probably a bit more than I should have (well without doing some extra welding.. which I didnt do. nuts/bolts all the way ). I knew this could potentially cause issues down the line, but for the time and all it was fine.

Now the XJ isnt the DD, so I am thinking about what to do next. Can anyone tell me how thick the unibody is? I know its probably out there somewhere, but I couldn't find it with a few searches and I am getting tired, got a long day ahead of me tomorrow w/ packing the Uhaul and driving all night tomorrow night, and just want to pass out.

What I am thinking is replacing the unibody frame rails with slightly thicker material, but something with the same dimensions, and making it be full boxed... aka making it more of a frame. Then I could either weld the body back onto this "frame" or I could add some structural support to the body and bolt it on (so it would essentially be a frame). I would probably be doing the floor pans as well since they are rusted out a bit (have makeshift patches in for now which are doing well... but might as well do it right).

Anyone got any advice on this? Good/bad idea? I love my XJ and I just dont want to run into a position where something gives out because the unibody is f**ked, and I figure if I could spend the time making frame stiffeners why not just go all out and redo everything?
Unibodys dont really tear to pieces a whole lot, they have very small bends and twists which are bad (caused by hard wheeling, huge axles, doors off, etc...) but the consequences are very small. What you would notice, which is why people worry about unibodys, is the doors not closing right, squeeking, not being able to properly fit control arms and such. Howeever, the problem will NOT be a severe problem. If your unibody is tweaked (read: *slightly* bent or twisted, not major/catastrophic damage) then your screwed. Welding some plates on isnt going to help. If done right it would help if you did it to begin with, but at his point i dont think there is any turning back.

That said you might still be alright.
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  #7  
Old January 17th, 2009, 01:03
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Mr_Random Mr_Random is offline
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Re: XJ Unibody rebuild

There's a guy on comancheclub and jeepforum that is looking to do the same with his XJ, he has some significant research, though. If anything, it'll be easier to find and contact him on comancheclub for any info you can extract.

I've THOUGHT about it, but just as a "what if" for quite a while now, but only the far future will tell what comes of these thoughts...
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  #8  
Old January 17th, 2009, 06:52
whitneyj whitneyj is offline
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Re: XJ Unibody rebuild

I'm a big fan of plating the rails with 3x3x3/16th" angle. I've heard of guys using "C" channel but I think that's overkill. Just plate the rails and build a couple more crossmembers tying both sides together. That would be the best option in my opinion. Anything past that, like building your own frame and bolting/welding the XJ on top of it, would take an immense amount of work that may or may not hold the same structural integrity of plating with Xmembers. Remember the XJ is a unibody, so once you remove the rails, that I would think holds the majority of the XJ together in working form, you've potentially opened a giagantic can of worms.
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  #9  
Old January 17th, 2009, 12:19
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DirtyMJ DirtyMJ is offline
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Re: XJ Unibody rebuild

Quote:
Originally Posted by Mr_Random View Post
There's a guy on comancheclub and jeepforum that is looking to do the same with his XJ, he has some significant research, though. If anything, it'll be easier to find and contact him on comancheclub for any info you can extract.

I'm probably 'that guy'. Long ways to go yet, but this picture is somwhat out of date (doesn't have a floor in the mid section anymore).




Quote:
Originally Posted by themangeraaad
So I have trimmed my rear fenders as far as I can and probably a bit more than I should have (well without doing some extra welding.. which I didnt do. nuts/bolts all the way ). I knew this could potentially cause issues down the line, but for the time and all it was fine.

Now the XJ isnt the DD, so I am thinking about what to do next. Can anyone tell me how thick the unibody is? I know its probably out there somewhere, but I couldn't find it with a few searches and I am getting tired, got a long day ahead of me tomorrow w/ packing the Uhaul and driving all night tomorrow night, and just want to pass out.

What I am thinking is replacing the unibody frame rails with slightly thicker material, but something with the same dimensions, and making it be full boxed... aka making it more of a frame. Then I could either weld the body back onto this "frame" or I could add some structural support to the body and bolt it on (so it would essentially be a frame). I would probably be doing the floor pans as well since they are rusted out a bit (have makeshift patches in for now which are doing well... but might as well do it right).

Anyone got any advice on this? Good/bad idea? I love my XJ and I just dont want to run into a position where something gives out because the unibody is f**ked, and I figure if I could spend the time making frame stiffeners why not just go all out and redo everything?

Unibody (uniframe...) thickness varies. A lot. I'd estimate it's in the area of 16 gauge for most of it. I never bothered to throw calipers on most of what I cut out, but I can use my trusted eyeball. Oh, it IS fully boxed. People will argue that; they're wrong. The floor is quasi-structeral, with the area over the rails being the important part of that. However, the area between the two rails is also important - it adds to the over-all rigidity of the structure. If you want to see an example of a frame that isn't boxed, a chevy 1/2 ton is perfect. Older ones would easily flex bad enough to have the box dent the cab in, and make it so the tail-gate couldn't open.

I thought about welding the body back on, vs bolting... Ultimately I decided to weld it back on. My reasoning is partially that I will never be inclined to remove the body again anyways, since my tranny tunnel will be removeable. Also, it is stronger to weld the whole thing back together as a single assembly. And, honestly, I have replacement rockers which would have made bolting it together so complicated that I didn't see the point. Oh, and I think this might be easier anyways - the factory floor and uniframe rails have some bizzare contours to them, making it hard to replicated exactly the same. By removing the floor and junking it, I can use mostly straight frame rails and save a lot of headaches.

I would question your motive. I've questioned mine. I had cut open my floor and found the inside of the frame rails to be rather rusty. It turned out that the damage was almost entirely confined to the area I had cut open. But, you don't realize that until you've cut the rest of it apart. At that point I was committed, and decided to make the best of it. The build has leaned towards bombproof anyways, as I wanted to build an expedition style rig (35s on D60s, NP241D tcase, links front and rear). The reality is XJ uniframe failures are actually fairly low. They crack in a few places, and get a little warped over time. People act like the world is ending when this happens. They're actually considerably stronger than most vehicles. You can jump a stock XJ and rarely screw things up too bad. Try jumping a stock chevy - I know of somebody who had his fall off the jackstands to the floor (about 3' at most) and it bent the frame to the point that he scrapped it. Likewise, an older toyota frame can easily break between the cab and box if you put a half cord of wood in the back...
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  #10  
Old January 17th, 2009, 14:45
themangeraaad themangeraaad is offline
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Re: XJ Unibody rebuild

Thanks for all the replies, and DirtyMJ, thats kinda where I am coming from. I completely understand that the floor pan of the XJ does, in a way, box the unibody frame rails. My initial motive was, well, it seemed like an interesting project. More importantly, though I figured if designed properly it could add quite a bit of structural integrity. Like you said, I have found *some* rust, but not too much. I am cautious of there being more than I have seen since I opened the rear up a bit at the fenders when I cut it a bit too much, and a bit of water may have got in there, some people said this could lead to LOTS of problems, and while I knew this when I got to that point, I couldnt turn back once there was an opening.. I am not anticipating an excessive amount of rust, but I figured I might as well check it out before I continue to build it and end up breaking something further on down the line.

My major motivator is that I want to go for the best trail rig I can. I want to open my fenders fully, and run 35s or 36s on a 4.5"-5" lift. Keep the center of grav low, large tires, low geared, etc. Throw a shaved 9" or 14 bolt under there, 44 up front, who knows where I would end up. I want, like you said, something bullet/bomb proof. Also, like you said, doing that would open up the option for other mods, aka removeable tranny tunnel, etc. I have an opening above my exhaust/trans x-member on the passenger side since my floor rotted otu there and I just patched it, already had the the removeable area help out a few times with exhaust work and when the transmission x-member nut snapped off in the rail..

Its just kinda a bunch of ideas that pulled together into this idea. It would allow me to strengthen, while cleaning it up, and just doing alot all at once.
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  #11  
Old January 17th, 2009, 20:10
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nosigma nosigma is offline
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Re: XJ Unibody rebuild

After you really wheel the piss out of it you will start to notice cracks in the hatch (if you have the fiberglass hatch), blown spot welds and a need to constantly (like after every trip) tighten the track bar bracket and steering box along with numb steering and some wandering. Sure signs of a chassis that has loosened up.

Step 1: Buy a MIG welder (I went 110V Miller)
Step 2: Buy an old hood and some scrap steel. Practice welding and then welding thick to thin.
Setp3: Buy as set of unibody frame rail stiffeners and weld them on (search on "Get Stiff")

If this makes a night and day difference in how the rig rides and steers then you also need to plate from the front bumper back to the frame rail stiffeners.

Here is how I did it.

http://www.naxja.org/forum/showthread.php?t=978413

You can also buy pre made plates and steering box plates.

Step 4: Weld the front plates on.

This is a big job. Took me a full weekend to do the frame rails and a two very long (like 15hr days) to weld up the front. This was after a full weekend spend cutting plate and several evening drilling about 60 rosette weld holes/bolt holes on each side of the front plates. Plate the bottom of the frame rail too if your really serious about this.

John
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  #12  
Old January 17th, 2009, 21:20
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Mr_Random Mr_Random is offline
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Re: XJ Unibody rebuild

Quote:
Originally Posted by DirtyMJ View Post





Yes, you ARE "that guy"!

My screen name is the same through all three forums, and I've posted in both your threads, so you may notice me.

These plans set forth so incredibly intrigue me... I totally wish I could do exactly the same, but there's no point. Especially for being a pre-college 18-year-old.

Do it and make my dreams come true! Ha.
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  #13  
Old January 17th, 2009, 23:17
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DirtyMJ DirtyMJ is offline
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Re: XJ Unibody rebuild

Quote:
Originally Posted by Mr_Random View Post
Yes, you ARE "that guy"!

My screen name is the same through all three forums, and I've posted in both your threads, so you may notice me.

These plans set forth so incredibly intrigue me... I totally wish I could do exactly the same, but there's no point. Especially for being a pre-college 18-year-old.

Do it and make my dreams come true! Ha.


Yeah, I remembered your name, so I was pretty certain it was me and my silly project you were talking about. The build is posted on a couple forums beside those ones, but I don't post the same information or updates in each.


Oh, themangeraad, you might read this if you want to hear some of my rambling thoughts:
http://www.cherokeetalk.com/forum/showthread.php?t=34

But like I said, I post different things in every forum, but I think that is one of the better explained ones... Or maybe the one on CC. I dunno.

Last edited by DirtyMJ; January 17th, 2009 at 23:36.
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