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How to stop unibody flex/torsion

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Desert4x4

NAXJA Forum User
Location
Phoenix
So I've spent the last year trying to figure out answers. I can deal with a bit of body flex, but it's really annoying hearing the whole body creaking when the weight shifts from one wheel to the other.

I've added front and rear hitches and Detours unibody Rok sylders (the bolt on style). Nothing changed with the twisting of the body.

I love the Detours Rok Slyder, probably the best thing I've done to my XJ, but for torsional rigidity, physics tells me we need some type of cross bracing between the uni-frails.

It seems to me that the whole body twists like a twizzler when you get it on two wheels (diagonally).

I've read posts saying that even after sleeving both rails and putting in a roll cage, this still exists.

The closest thing I've seen to a "brace" between the rails, is the JKS rear shock mount. But that doesn't even bolt to the rails, and I doubt it would change anything.

Would a bolt in rollcage thats bolted to the floors, even make a difference?
 
For me, the roll-cage made the difference. The stiffeners did not. Now I can have my heep all twisted up on the rocks and still open the hatch and doors normally. Getting the cage tied into as many points as possible makes a world of difference. I don't hear any more creaks and pops.
 
plate frame front to back. Very well tied in cross member. Good bumpers tied in front and rear. track bar cross brace. full cage, like at least a 10 point cage.
 
jrowell said:
For me, the roll-cage made the difference. The stiffeners did not. Now I can have my heep all twisted up on the rocks and still open the hatch and doors normally. Getting the cage tied into as many points as possible makes a world of difference. I don't hear any more creaks and pops.
Click to expand...

Thanks for the reply jrowell. If you don't mind, what kind of cage did you get? Or did you make it yourself?

I remember seeing a picture of a cage that went from tubing to plating at the driver's left knee area, so it was wedged betweeen the side of the car and the dash. Looked kind of clean. Can't find the picture again though.
 
blondejoncherokee said:
plate frame front to back. Very well tied in cross member. Good bumpers tied in front and rear. track bar cross brace. full cage, like at least a 10 point cage.
Click to expand...

Did you notice any less creaking with that track bar brace? I see how it would definitely the front portion of the rails, but since it's in front of the springs, would it do much to keep your hatch from binding up, and door seals from squeaking, ect.

BTW, your cherokee must be pretty stiff with all that!
 
Frame plating bumper to bumper on at least 2 planes, 2x6 replacement rockers with multiple support legs to the plated rails, full cage mounted off the rockers and plating, hybrid design with multiple areas tied back into the body, full halo completely welded to the gutter rails, etc etc
 
ya forgot to mention I run the 2x6 rocker replacement too. foxwar71 is right about the 2 planes minimum front to back.
 
Desert4x4 said:
Thanks for the reply jrowell. If you don't mind, what kind of cage did you get? Or did you make it yourself?

I remember seeing a picture of a cage that went from tubing to plating at the driver's left knee area, so it was wedged betweeen the side of the car and the dash. Looked kind of clean. Can't find the picture again though.
Click to expand...

I made mine. It's a hybrid cage welded in at as many places I could think of.
 
I think best results for chassis stiffening are going to be rocker replacements and a cage that is tied, with sheet metal, to the A, B, C & D pillars. Don't just set the cage in place and weld it to the floor - connect it to everything in sight. Firewall, pillars, the channel across the bottom of the back seat, you name it - add tube & plate things to the plating.
 
yep. I assumed it was obvious by the time you do a cage you already have 2x6 rockers and frame plating. and that its just common sense to tie into the frame as much as possible. I wouldnt trust just going straight into the thin sheet metal in the XJ floor.
 
frame plating is nice, but remember, it's still just a ladder frame even if it's replaced entirely with 1/8 wall box tubing. It'll still twist, just look at an F350 or ram 3500 on the ramp test to see an example... those are full framed trucks and they still twist because they're still just a 2D ladder frame.

You gotta make the chassis effectively 3D (as in, add a well triangulated cage) to actually make it flex/twist less. No way around it. So yeah, plan on a cage if you want it to not do that.
 
kastein said:
frame plating is nice, but remember, it's still just a ladder frame even if it's replaced entirely with 1/8 wall box tubing. It'll still twist, just look at an F350 or ram 3500 on the ramp test to see an example... those are full framed trucks and they still twist because they're still just a 2D ladder frame.

You gotta make the chassis effectively 3D (as in, add a well triangulated cage) to actually make it flex/twist less. No way around it. So yeah, plan on a cage if you want it to not do that.
Click to expand...

Just watched, again, the video of the Dodge vs. Ford pickup flex test: http://www.youtube.com/watch?v=_f3CAnH7WIM

I've actually seen it before. Still amazes me how much the Ford frame flexes. If the XJ did that, it would rip the roof off.

OK. I was thinking back to my physics days, and a 3D type of structure definitely is needed to help isn't it. I guess the $1k Rock Hard cage is the way to go for a non-welder.
 
That is actually exactly the video I was thinking of when I wrote that :thumbup:

That's just the difference between a fully boxed frame and a C channel frame. The XJ unibody is spotwelded stamped sheetmetal, and I don't know about anyone else, but I can't get my hatch to close right if it's flexed out when I open it.
 
I don't even get why people are so hot on frame stiffeners fixing the body flex issue. The only real way to reduce/stop body flex is to do a graphed weld-in cage. If you look at a drift car for example, you'll notice all of the dimpled tie-in plates connecting main tubes to A and B pillars. Trussing the body is what reduces flex. Slapping thicker plates on unibody rails does not much more than give you better anchoring for suspension.

Look at the guys who have stiffeners and really wheel their truck, they still get large amounts of body flex...
 
s14unimog said:
Look at the guys who have stiffeners and really wheel their truck, they still get large amounts of body flex...
Click to expand...

Speak for yourself. Even before I had my cage I had virtually no body flex. No issues with panel gaps or opening doors/hatch.
 
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