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Uni-Body Cracks and flex..Need Help

E

Explorer 1

NAXJA Forum User
Location
Whittier, Ca
Both my driver's side and passenger's side door have started rubbing at the top front. You can see where the paint had chipped off by the rubbing in these pictures.







Obviously the uni-body is flexing somewhere in the front. I have several modification to this vehicle that have added significant weight. I already have installed T & J's frame stiffners which run along the frame rail the same length as the rock sliders.

I can see a hairline crack running from the roof drip rail to the windsield which indicates that the roof is being pulled down when the vehicle is subject to extreme flexing.

I can replicate the flexing by raising the vehicle on my lift when I place the lift pads on the frame rail just behind the engine compartment. The flex is bad enough that when on the lift, the two front door will not open or close.

Do anyone know where I need to add additional reinforcing to the unibody to counter the flexing?

I don't need guesses, so if you don't know don't speculate.

Thanks in advance for your help.

Fred
Explorer 1
 
Jes said:
A properly designed and implemented roll cage will alleviate your issues.
Click to expand...

This.

Nothing sort of a cage is gunna keep the roof and upper area of the body from m moving around. When I built my cage, I bent up my halo to hug tight to the dip rails. The dip rails are welded to the halo down the entire length of each side. Now the roof and body go nowhere.
 
and you need not go to the expense or complexity of a nascar or nhra cage, and i agree build the hoops close to the body and then join them to the unibody. you could consider hoop behind driver seats and one behind rear seat and then from floor along sides of dash area up to driver area hoop and so on and join and brace as needed. you can also go basic and then add bracing later as your finances allow.
good luck and ask lots of questions!

Jes said:
A properly designed and implemented roll cage will alleviate your issues.
Click to expand...
 
You need to tie the cage into the points where the suspension connects to the body (ideally). This will help take some/most of the load off the body.

Nothing wrong with tying into the drip rails/etc., but I think you'll notice the most improvement from tying into the coil/bumpstop mounts and leaf spring mounts.
 
xwhatever... cage or it's gonna keep happening.

My unibody flexes enough that it slowly wiggles the passenger side of my rear cab glass (MJ) further and further over in the frame until there is a 1/2" gap. That pane isn't even supposed to open, I have to push it back over with a 2x4 every few months.

No matter how much you stiffen the frame rails, they are still mostly in a flat plane, which means they won't do much for torsional rigidity of the chassis. If you want that, you need a cage, and to tie it in to the unibody in a few spots up near the roof. As MoparManiac said, tying it into the suspension mount points will help significantly as well.

Other than that? Weld the doors on I guess. That should stiffen things up a bit, it kept ktm racer 419's 2 door XJ together for a lot longer than that thing should have lasted - after it fell apart so bad that the roof and floor/frame rails kinked at the B pillar and the doors literally wouldn't fit the openings. He had to portapower it back into shape, weld up the cracks, slap the doors back on and weld them on with plate to make it stop taco-ing.

That reminds me, you need to check elsewhere for cracking as well. A few troublesome areas:
* at the bases of the A-pillars, behind the top rear corners of the front fenders
* foxwar71 said his entire trans tunnel was cracked to hell when he pulled his jeep apart
* on 2 doors, the areas around the vent louvres in the B pillar door jamb love to crack
* while you're at it, check the frame by the steering box and track bar mount

I am sure there are other places but it has been too long since I stopped looking at my old XJ for me to remember. The rest of the spots I've seen the unibody crack in are all MJ specific.
 
kastein said:
My unibody flexes enough that it slowly wiggles the passenger side of my rear cab glass (MJ) further and further over in the frame until there is a 1/2" gap. That pane isn't even supposed to open, I have to push it back over with a 2x4 every few months.
Click to expand...


hey! mine does the same thing except on the drivers side :gee:

i've been wondering how to solve the issue but in the mean time i just shove it back over every now and then.
 
I just finished taking the whole thing apart, welding the spots where I found any cracks, replacing all the rubber and then painting the whole thing.......I was so looking forward to getting it back on the trail so I am looking for a way that I won't have to paint it again.

Since I do most of the work myself, progress goes rather slowly....but if I have to add some kind of external bracing I guess I have no option.

Here is what it looks like now after all the work:









Thanks,
Fred
Explorer 1
 
The roof bar should be closer to the roofline and overhanging it a tad to protect the body.

What is the cage attached to on the bottom of each leg?
 
mako my day said:
Pre bent cages? Any more info on this? Do tell more Chris@TJ. Linky no worky
Click to expand...


Yeah that link is having some hick ups lately try it again a little later its hit or miss right now unfortunately . I am 99% sure that Souske is running our cage. He recently said " Still $699? heck of a deal for the best weld in kit on the market" As well as many of the Jeepspeed guys. But like I said pre-bent & pre-notched just need to be welded in and will even tie into our Barnett Performance chassis stiffeners for an even stouter set up. The cage covers A,B,C and D pillars with roof bars going across, with sandwich plate to the floor... I hope this link works we started with our Barnett Performance cage on this build and added from there. http://tandjperformance.com/pics/Steve-Pohls-1999-Jeep-Cherokee-XJ?page=1
 
Last edited:
Thanks for some good advice. Before I commit to any course of action I want to be sure it will work.

I think I will set some lazers lines up and then slowly lift the vehicle so I can measure where the unibody is actually flexing, then see what is available in the market place to correct it. Then if necessary, fab my own solution.

I currently have an internal roll cage, T & J frame rail stiffners, steering box reinforcement ( both sides) and a track bar brace. I just want to be sure before I throw any more money and time at the problem.

Thanks,
Fred
Explorer 1
 
You can't spot reinforce these things....you need to reinforce the whole chassis with plating and caging bumper to bumper to make them last. :doh:
 
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