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Discussion Starter #1 (Edited)
Has anybody ever just chopped off the bottom section of the frame rail, leaving the 2 vertical pieces, drilled holes along the existing sheet metal frame for rosette welds, then just put square/rectangle tube inside of the stock frame and welded it up for strengthening, instead of plating the outside of the stock frame? The last time I did a Cherokee I plated the outside and it worked all right, but it seems if you could put in an existing shape it would be structurally stronger.
 

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I like the idea never seen it before
best of both worlds unibody on frame construction & just add 200lbs
 

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definatley sounds like a good idea. I need to do some reinforcing this summer before i start wheelin my newest XJ very hard. I might try this, if I do I will definatley post some pics!
 

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Reinforcing the XJ needs to be looked at as a whole. By reinforcing something, you simply transfer a week point somewhere else in the chassis. However, most that plate there frames with sufficiant material and do it correctly rarley have failures. Did your plating fail?

To answer the acctual question, yes there are some that have done similar mods. As far as I know it worked fine. But froma logical standpoint is it really worth the extra work to aquire a minimal strenght increase? To me...no.
 

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Unless u r going to go hole hog, cut the uinibody "frame" off, build a compleat sub frame and do body mounts... I would say no as well

Smart frame plateing and crossmember will be ur best bet
 

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Discussion Starter #6 (Edited)
My frame plating didn't fail, I'm just looking for a better way to do it next time. I'm going to be very weight-conscious with the MJ, and I'm considering using 1/8" thick box tube instead of the 4"x6" 1/4" wall box tube that I cut in half last time and used on the outside. My design goal is not the biggest, baddest hard-core rig weighing 5000 lbs. on 40's, but rather to turn the MJ into a small, fast, cheap side-by-side/Rockcrawler hybrid. Seems thinner wall box tube would provide more structure and a stiffer chassis compared to welded together plates. Granted it wouldn't provide the dent resistance of 1/4", but this idea could be done with thicker tube as well for those with different design goals. At least in my head the idea seems to require about the same amount of work as the method I used last time. Once cutting off the bottom of the stock rails, you could simply slide the box tube up and back down to shape it right before finally welding it to the chassis. Since I'll be redoing the suspensions anyways, the fact that a lot of the suspension bracketry will be cut off doesn't factor in. You could do it in sections like a lot of people plate the outside, preferably doing as long a section as possible before welding it to the unibody.
 

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I'm considering using 1/8" thick box tube instead of the 4"x6" 1/4" wall box tube that I cut in half last time and used on the outside.

At least in my head the idea seems to require about the same amount of work as the method I used last time.

Once cutting off the bottom of the stock rails, you could simply slide the box tube up and back down to shape it right before finally welding it to the chassis. Since I'll be redoing the suspensions anyways, the fact that a lot of the suspension bracketry will be cut off doesn't factor in. You could do it in sections like a lot of people plate the outside, preferably doing as long a section as possible before welding it to the unibody.
1st line: 1/4 was overkill to begin with. However the same idea in 1/8 is proablably plently sufficient, designed and exicuted correctly.

Line 2: Meehhhh....Id say both take a considerable amount of time.

Line 3: Good plan...do it. Report back in the TOTM for unibody reinforcement. :p
 

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Reinforcing the XJ needs to be looked at as a whole. By reinforcing something, you simply transfer a week point somewhere else in the chassis. However, most that plate there frames with sufficiant material and do it correctly rarley have failures. Did your plating fail?

To answer the acctual question, yes there are some that have done similar mods. As far as I know it worked fine. But froma logical standpoint is it really worth the extra work to aquire a minimal strenght increase? To me...no.

x2, your just gusseting a beer can as it is, plate around the outside and youll be okay
 

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Have you ever seen the inside of the "frame rails"? There are multiple other pieces inside of them in different spots, they are not just hollow = way more work to clean them out and put it inside. If its done right on the outside it will be plenty strong and lighter
 

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Well

I was thinking about drilling large holes like 1andahalf inch in the subframe and welding in tubes that would be like bushing mounts and putting rubber bushings in there with a bolt that goes through those into a u channel steel frame??
Get the idea

kinda think like dimples with steel tube inside through the frames sideways
 

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every time you wanted to weld something to the frame, you'd have to cut the uniframe out of the way to get to the good metal. so that kinda kills the "it looks cleaner"
 

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Mine's plated in 1/8"...

as for cutting the uniframe off and running body mounts.... i've tried it... the best way to do it has already been done and the guy has a build thead here, i wanna say his name is 2doorx4... the build is a red 2 door that he completely gutted everything from the bottom of the pillars and basically did a rocker replacement with 2x6x.188 and built in from there...


like i said.. just cutting the uniframe off isn't enough, the floor GREATLY relies on those frame rails for structure..

here's some pics of my attempt/superfail





 

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As mentioned, the stock rails are not straight on the inside. There's a lot of all sorts of crap inside them that needs to be cut off if you want to fit a box tube inside there. And as said, if you need to weld anything on the rails, you'd need to cut off the stock sheetmetal so you can weld in the box tube. I recommend either plating or cutting off everything and using box steel.


I did mine a bit in the same way as OnetonXJ.. my uniframe rails were pretty rusty in some areas, and living in Finland where most people coat the unibodies with thick rubbery undercoating which is next to impossible to clean out easily, I cut off everything and did a new "frame" fomr box steel.

Far from finished here, but you get the point. ..and this is no way the easiest method, in the end I'm pretty sure removing undercoating + plating would've been easier and faster :shaking:



 

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here's how i did mine, i plated the front and had tnt frame stiffie's on it from before when i did boatsides. So i chopped off the unibody just before the front spring hanger and sleaved the new frame rails about 3 1/2 feet and rosette welded them thru the unibody and stiffie's, i then cut up the inside and of the rails and pulled them in and welded it, turned out great, once the tube work is all done it should never tear apart.



 

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here's how i did mine, i plated the front and had tnt frame stiffie's on it from before when i did boatsides. So i chopped off the unibody just before the front spring hanger and sleaved the new frame rails about 3 1/2 feet and rosette welded them thru the unibody and stiffie's, i then cut up the inside and of the rails and pulled them in and welded it, turned out great, once the tube work is all done it should never tear apart.



Did you get this finished?
 
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