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Full frame

K

Keithmania

NAXJA Forum User
Location
Zanesville, OH USA
Was wondering if anyone had thought about building a full boxed frame and then making mounting points on the existing XJ unibody and mating the 2 together. Would you get any more torsional rigidity with the full frame? Would using the unibody frame rails as the mounting points work?

My sense of it is that it would add lots of rigidity to the existing platform and would allow some greater ability to customize what kind of suspension you want to put under it. Additionally, if the engine mounts were moved from the unibody to the new frame could you not put in an engine that had whatever combination of torque/hp specs you'd want? As long as the engine would fit within the confines of the XJ engine bay.

Just thinking out loud...
 
I suggest something other than wood for your body mounts, or something less than 10 feet tall.

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I am working on replacing my MJ's whole frame with box tubing, but it will be welded to what's left of the cab and fenders, so not what you are looking for. And everyone (so far) who has heard of my plans has said I'm retarded for thinking about it, so take this as you will.
 
Tim_MN: LOL, thanks for the pics.., made my day before I drive out into the wintery night-time blizzard commming at me, headed for work.

Keithmania: Why not sell what you have, get an older full frame Cherokee, or Wagoneer, and join a different forum? My old '79 was, hands down, superior to my '89 XJ. Higher horsepower, rigid frame, strong differentials, comfortable, more carrying capacity, and my mileage with the underpowered 258 was around 20mph, which is about the exact same as my XJ.., but I could do more with the '79, anytime, anywhere, anyhow.., pull a ton and a half of anything for thousands of miles too. Rebuilt the engine at a quarter of a million miles, and really did not need to. Close to 300k on the odo., when the frame gave up to the damned salt. Has a nice engine though, lol.
 
Alaskan89XJ said:
Tim_MN: LOL, thanks for the pics.., made my day before I drive out into the wintery night-time blizzard commming at me, headed for work.

Keithmania: Why not sell what you have, get an older full frame Cherokee, or Wagoneer, and join a different forum? My old '79 was, hands down, superior to my '89 XJ. Higher horsepower, rigid frame, strong differentials, comfortable, more carrying capacity, and my mileage with the underpowered 258 was around 20mph, which is about the exact same as my XJ.., but I could do more with the '79, anytime, anywhere, anyhow.., pull a ton and a half of anything for thousands of miles too. Rebuilt the engine at a quarter of a million miles, and really did not need to. Close to 300k on the odo., when the frame gave up to the damned salt. Has a nice engine though, lol.
Click to expand...

xjs are lighter, quicker, cheaper. the carbed 4.2 in an fsj is terrible in comparison to the more modern fuel injected 4.0. unibodies can be strengthened for abuse. and frames break too. my beat to hell xj with a and b pillar failure is still more rigid than my rust free 78 j10 frame.
 
kastein said:
I am working on replacing my MJ's whole frame with box tubing, but it will be welded to what's left of the cab and fenders, so not what you are looking for. And everyone (so far) who has heard of my plans has said I'm retarded for thinking about it, so take this as you will.
Click to expand...

way too muck work, especially when plating around the existing rails will yield the same strength gains
 
Oh forgot to mention. If you were to get an older Cherokee, just do not get the 360 AMC V8 engine. It's Crap. You can build up a 258 straight six with few after market items such as a 3/4 race cam, etc., 4-barreled carb/manifold, etc. Adapting another make high horse power V8 is within the realm too. In correction to my earlier post, another fellow I knew had the AMC V8, which had the higher horsepower, but less low end torque than the straight 6, so I could out perform his machine in tough places.
I think I have read that some magazine group got 700 horse, plus, or minus out of their XJ 4.0 engine. Good chance that a similar mod. to an AMC straight six would do all that you would ever want to do.., but suffer the gas mileage. But really, my old six would get me anywhere I wanted to go along with most anything else stock out there, including my XJ. Well, my XJ, I am certain, could never match the abilities of my old '79'er. Even in death, it sure looks good in my yard, as a monument to when Americans made American things.., until NAFTA, and GAFTA,(sp?), began to INVADE the parts stores with replica parts, dimmer switches, and such.
 
Alaskan89XJ said:
my XJ, I am certain, could never match the abilities of my old '79'er. .
Click to expand...

im currently building a fsj and im sure it will never be as capable as my cherokee. a lot heavier, and a lot bigger.

will look more badass though.
 
Hey, I could see that with the J-10, as it's a pick'em-up, not a full on station wagon strengthening the entire frame. But whatever, In Ford, Chevy, Dodge, Jeep country.., if you listen very carefully in the quite of night, you can hear them rust. Unibody, HA! If I had bought my '89 in '89, and not in 2010, and had strengthened the entire unibody so-called chassis design flaw, and et al, then maybe it would be in better condition in it's one decade shorter life compared to my Model 17. Same roads, but I would say if I pulled a brand new '79 model 17, and a brand new '89 XJ out of storage and drove each one on alternate days, the 17 would outlast the XJ. Not only that, but I am not racing.., the lighter, faster bit. How fast do you go on one lane forrest trails, rock paths, etc. My 17 would go down the highway at 75 mph all day, or night. How fast do you need to go? Try hauling heavy gear, or a boat, or another vehicle with the XJ without modifying it to all beat out! You know what.., an XJ is just like a boat, a hole in the water in which you toss your money into. In our case, a box on wheels constantly requiring $$$ upgrades to meet the needs that any old good condition Cherokee could perform without the $$$ mods. CHEAPER??? Ok, I am biased.., lol, so what? I've spent a couple of grand for better than OEM XJ suspension, and bumpers, just to approach the OEM Model #17. ...and show much more for real axles, transmissions, transfer cases, propeller shaft mods., braking, and breaking things.., seems the $$$ list is endless.

I think a tubular chassis for an XJ is quite the good deal if done properly. --OR-- plating up around the seams/welds, etc. Seems such a machine could go BAJA on us. Take pics, and vids will 'ya?
 
ktm racer 419 said:
way too muck work, especially when plating around the existing rails will yield the same strength gains
Click to expand...
I'm not gonna put it through FEA and prove it with numbers, but this is wrong... not sure by how much, but it is. Even just plating the frame all the way around leaves you with a C channel capped by a spotwelded piece of 16ga. And I don't have much left to plate, it's rusted through in a couple spots and what's left is just as thin :gee:

Oh, and my floor is gone, so by the time I finish cutting that out, I might as well just stuff box tube under it and weld a new floor on after.
 
Alaskan89XJ said:
Hey, I could see that with the J-10, as it's a pick'em-up, not a full on station wagon strengthening the entire frame. But whatever, In Ford, Chevy, Dodge, Jeep country.., if you listen very carefully in the quite of night, you can hear them rust. Unibody, HA! If I had bought my '89 in '89, and not in 2010, and had strengthened the entire unibody so-called chassis design flaw, and et al, then maybe it would be in better condition in it's one decade shorter life compared to my Model 17. Same roads, but I would say if I pulled a brand new '79 model 17, and a brand new '89 XJ out of storage and drove each one on alternate days, the 17 would outlast the XJ. Not only that, but I am not racing.., the lighter, faster bit. How fast do you go on one lane forrest trails, rock paths, etc. My 17 would go down the highway at 75 mph all day, or night. How fast do you need to go? Try hauling heavy gear, or a boat, or another vehicle with the XJ without modifying it to all beat out! You know what.., an XJ is just like a boat, a hole in the water in which you toss your money into. In our case, a box on wheels constantly requiring $$$ upgrades to meet the needs that any old good condition Cherokee could perform without the $$$ mods. CHEAPER??? Ok, I am biased.., lol, so what? I've spent a couple of grand for better than OEM XJ suspension, and bumpers, just to approach the OEM Model #17. ...and show much more for real axles, transmissions, transfer cases, propeller shaft mods., braking, and breaking things.., seems the $$$ list is endless.

I think a tubular chassis for an XJ is quite the good deal if done properly. --OR-- plating up around the seams/welds, etc. Seems such a machine could go BAJA on us. Take pics, and vids will 'ya?
Click to expand...
im building my fsj to be a go fast rig. not so much technical rockcrawler as i would have a hell of a time fitting it through the same trails my cherokee navigates. a half ton truck is more heavy duty than a quarter ton xj that i cant argue with, but a xj can be made into a much more capable rig offroad for less money is what im saying.
kastein said:
I'm not gonna put it through FEA and prove it with numbers, but this is wrong... not sure by how much, but it is. Even just plating the frame all the way around leaves you with a C channel capped by a spotwelded piece of 16ga. And I don't have much left to plate, it's rusted through in a couple spots and what's left is just as thin :gee:

Oh, and my floor is gone, so by the time I finish cutting that out, I might as well just stuff box tube under it and weld a new floor on after.
Click to expand...

friend of mine had his floors rot out so he tore the remaining bits of floor out and plated his entire rails from the inside. i think even that would be easier to execute than fabricating an entire frame. it was completely boxed as well. i just think making a new frame is a waste of time when we have figured out how to make the existing unibody structure last with stiffeners, cages, and key reinforcements.
 
ktm racer 419 said:
friend of mine had his floors rot out so he tore the remaining bits of floor out and plated his entire rails from the inside. i think even that would be easier to execute than fabricating an entire frame. it was completely boxed as well. i just think making a new frame is a waste of time when we have figured out how to make the existing unibody structure last with stiffeners, cages, and key reinforcements.
Click to expand...
I actually sorta did that on my 96. I sleeved it with 3x6 quarter wall tube with the top cut off, and drilled rosette weld holes through the frame all over the place. Slid the tube on and welded it from the inside while holding it with a c-clamp.

But I'd rather have a frame I can go full retard on without ever damaging, that is sealed completely and won't rust out from the inside, and will probably last forever.

We'll see whether it works out or not. My estimate is approx. 470lbs frame weight (and that's probably a little over.) Shit, I've wheeled it with more crap than that sitting in the back. And that's not including cutting the old junk off, so I can probably save ~150-200lbs there.
 
idt rather treat xjs as disposable vehicles than do that
 
Frame stiffeners and call it a day. Adding a frame under a frame is and always will be ghetto fab.


As for fullsize vs compact. Most trails were I am the most badass fullsize rigs get their asses handed to them by an XJ/TJ/JK/ZJ on 33's with lockers. They are to tall, to wide, to long the list goes on.
 
Once you cage it and tie into the suspension points, you're taking a major load off of the unibody.

Like Sam (ktmracer) said, key reinforcements (like steering box/track bar area) will also help.

I would think it's more work to build a full frame with body mounts, suspension mounts, steering box mounts, etc. then to cage and stiffen the existing unibody.

And Ken, if your rails are rusted that bad it's a lot easier to start over on a new chassis.
 
If I had plenty of money, a well set up shop to work in and lots of time I would get an unmolested XJ and strip it down to the shell. After properly bracing the body I would cut the bottom out of the frame and make some 2 1/2" x 4 1/2" (or whatever size best fits in the existing frame rails) rails to fit the entire length of the chassis. I would also form up some 1 1/2" x 3" rails to go laterally across the frame conforming to the shape of the floorpan and tranny tunnel in 3-4 places. I would make a custom front bulkhead with reinforcements for the steering box and bumper mounting. I would do the same in the rear. Then I would build a custom cage with a full engine cage designed to add to the rigidity of the chassis. This would be a hybrid internal/exo cage. I would build tube fenders front and rear with room for 36" tires. From there I would do up a custom suspension, 4 links front and rear with coilovers. So basically I would build something like a KOH race truck but street legal :D
 
jeeperjohn said:
If I had plenty of money, a well set up shop to work in and lots of time I would get an unmolested XJ and strip it down to the shell. After properly bracing the body I would cut the bottom out of the frame and make some 2 1/2" x 4 1/2" (or whatever size best fits in the existing frame rails) rails to fit the entire length of the chassis. I would also form up some 1 1/2" x 3" rails to go laterally across the frame conforming to the shape of the floorpan and tranny tunnel in 3-4 places. I would make a custom front bulkhead with reinforcements for the steering box and bumper mounting. I would do the same in the rear. Then I would build a custom cage with a full engine cage designed to add to the rigidity of the chassis. This would be a hybrid internal/exo cage. I would build tube fenders front and rear with room for 36" tires. From there I would do up a custom suspension, 4 links front and rear with coilovers. So basically I would build something like a KOH race truck but street legal :D
Click to expand...
this is what I was dreaming up for my next XJ. But there are millions of XJs and they aren't as cool as MJs. And MJs have the bonus of only having to deal with about 3-4 feet of frame rail being attached to the body/floor when you're considering something like this - the rest is already designed to be similar to what I'm planning.

And I happen to have an MJ with very little of its frame or floor left already. If I cut the firewall, inner fender walls, and back of the cab off the frame I could probably lift my cab off today.

PS: not sure what size fits inside the frame rails on an XJ, but 3x6 1/4 wall fits the outside like a glove, at least from the rear crossmember to about the front leaf hangars.
 
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