Welding Center Frame Stiffeners

Ok, me and friend got center frame stiffeners, we are doing one of the jeeps now.

1. is it true the factory frame has a zinc coating?

2. how have you all tied in the legs for a rocker rail, i.e. slider? drill and tap threads into the stiffener, or weld nuts to stiffener. I figure just drill and tap 3/16 inch thick is more than enough for a fine pitch bolt to give enough threads.

3. we will be adding a weld on nut for extra bolts for the tranny mount cross bar. both of us have run into stripped factory threads, this will give us additional cross bar bolts.

4. Any other advice?

Can't speak for your year, but my 2000 is.

Yep sure is. My sliders are welded. No need to have them bolt on if you don’t have to in my opinion.

I've drilled and tapped into all 3 of my XJ center sections. I used 3/8"-16 bolts with no issues at all.

Try and get the metal as clean as possible. I've used various methods to get rid of the undercoating first. I've tried a heat gun, flap discs, wire wheels, etc. On my 99, I did front to rear and used a heat gun with a putty knife. It was slow, but it worked. I then used acetone to clean up the residue I don't have a favorite on taking off the undercoating. Just use what works best for you.

After the undercoating was removed, I used flap discs to grind off the paint. One thing I did notice was that you'll get down to what you think is bare metal, it looks gray and like bare metal, but it must be the zinc coating. You have to go a little farther than that. You'll see what i mean if you look closely.

In the hard to reach corners and such, I used a die grinder with smaller bits and burrs. You can use small putty knifes, screwdrivers, or anything else small to scrap in those hard to reach areas. After it was all ground down, I cleaned it with acetone again, and started to weld.

It takes a while and you have to be patient. Take your time, and most of all make sure your weld areas are clean. You'll have the most trouble with your welds if they are not clean.

Every-time I weld something, I can always hear my old high school shop teacher, Mr. Post. He always said, "if you're welding something, it must be scrupulously clean!" I hear that to this day.

ok, great advice, thanks!

now here is a thought, leave the factory zinc coating and weld thru it? weld thru paints are often zinc loaded, so the thin factory layer of zinc aint much different I would think. sure the weld wont be as clean as if you take all the zinc off, but if you use weld thru primer anyway, why remove the zinc plating? It is not like these welds must be perfect, pin hole free, as if we are welding on a nuclear reactor vessel. Id think the factory applied zinc plating is far better adhered and makes a better corrosion inhibitor than a rattle canned weld thru primer that Id apply. I will put the weld thru primer on the stiffener, as they are bare steel.

Any thoughts or experiences welding thru the factory zinc? (factory paint, under coating and such removed of course)

Take your time, remove undercoating: Heat, scrapper, super goo gone pro works great for left over smears. Follow with acetone or such.

Once thats cleaned off, spend lots of time making sure the stiffener fits as close as possible (clamps, jacks.....) Then mark the areas you plan to weld ONLY. Dont skimp this step, ide even recommend mocking it up again after youve marked and removed it.

Sand said areas but not too far, the metal is thin as it is. Look for clean good metal, it doesnt take much to get there.

I tried upol gold weld primer. It was pissed attempting to weld through it so I scrapped it off all areas that I was welding and left it on the mass surface area to protect the stiffeners.

Go Slow, be patient and MOST IMPORTANTLY! Wear a respirator if you plan on burning through any nasty metal primers or zinc on the body!!!

1990JEEPXJ said:

Yep sure is. My sliders are welded. No need to have them bolt on if you don’t have to in my opinion.

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That is interesting, I had heard it was not good to weld the rock sliders on, rather bolt them, cause they can be damaged and if welded not as easy to replace. It was likened to not welding my front bumper to the frame, it will stay a bolt on bumper.

But, hey that was just an inter net opinion I read, and I am learning this jeep stuff, first time.

Got to give this some thought. pros, cons?

We, me and a friend both got XJs, and both got the stiffeners to install, he had sliders already, and I bought a pair, same as his. I got drop control arm brackets to deal with around the frame stiffener, his is stock control arm bracket. We got his stiffeners trial fitted yesterday, we marked places we will add weld nuts for tranny cross bar mounting bolts to supplement the stock weld nuts, thus cross bar will be held with four bolts per side, two stock, two added.
after weld nuts installed, brush paint inside of stiffener with two part DP epoxy, leaving bare area in weld zones. two coats. after last DP epoxy coat cures, rattle can weld thru zinc on bare weld areas. outside of stiffener remains bare.
clean off the paint and under coat off frame in weld zones, then apply zinc weld thru rattle can primer to the bare weld zones.

Refit the stiffener stiffener and weld it on. after which wire brush the weld areas, and paint the the exterior of stiffener, and bare frame areas with two coats DP epoxy.

I am not a fan of using sealer chalk around the seams at all. It will never remain sealed, water, salt water, dirt, etc will enter the frame and and work it's way into the double layer created by the stiffener. Far better to have a free flowing pathway from top of stiffener to bottom, a bottom drain so that the double layer space can be easily and fully flushed with a garden house.
If you got every thing sealed up, yet some how water, perhaps salty water gets in, you will not be able to rinse it well, if at all if the top is all sealed and there are few drain holes.

If you see salted roads, drive on an ocean beach, wheel near the Great Salt Lake, or many salt rich deserts in California (Saline Valley, were even the dry dust is corrosive and must be thoroughly rinsed out of the frames when you get home) then you NEED I think to be able to readily flush the space between the stiffener and frame, and use of sealers along the edges inhibits good flushing. What you all think about that, dumb idea? :confused1


THANKS!:bunny:

If it is sealed how will anything get in there?

Whoever mentioned the zinc metal looking like bare frame has me worried about mine. I had almost no undercoating to scrape. Just hit it with a flap disc until it looked like bare metal then primed it with cheap weld through primer. Haven’t welded the sliders on though.

89Mock said:

If it is sealed how will anything get in there?

Whoever mentioned the zinc metal looking like bare frame has me worried about mine. I had almost no undercoating to scrape. Just hit it with a flap disc until it looked like bare metal then primed it with cheap weld through primer. Haven’t welded the sliders on though.

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water can get inside the factory frame, it readily flows thru the front bumper end, which is open, then there are drain holes, and bolt holes in the factory frame. these will give access to water getting in between., Now one can seal every hole, seal every bolt head that sticks thru, and seal around the perimeter of every factory drain hole that lines up with the stiffener drain hole. But if there is any leakage between, that leakage will be trapped and cant be rinsed out effectivily.
Now you go wheeling and drag the stiffener over a rock, or come down hard and dent it. if the stiffener gets bent, the sealing maybe compromised, so water gets in, but without drains, how does it get out?

I just dont see trying to keep it water tight as an option, as there are too many ways for water to get in, and regular wheeling use will likely cause a sealant failure. it just takes one leak, and specially if the water or dust is salty and you will have trapped water, it wont drain as the drains are sealed it cant be flushed out.

thats my concern with sealing it, sealing it prevents flushing it out, and sealing wont be or wont remain perfect me thinks

Wear earplugs when welding, nothing like a little weld spatter in the ear canal. just use a flap wheel until you see sparks then weld. Weld the rock rails direct to stiffeners and paint.

stop over thinking it.

As Brian stated, stop over-thinking it.

I welded up my rocker sliders after cutting out a great deal of sheet metal to make room for it. I believe I used 2x3" or 2x4" .120 wall rec tubing and I welded those suckers in back in 2005. After a decade and a half of wheeling, with plenty of slams down on the sliders, there is no issue with welding them in. They are more secure being welded in anyways than several bolts could do.

I did tie them in to my reinforced frame rails with 1.5" HREW .120 wall tubing, as well as a full roll cage made of the same material also being tied in to the frame rails... all has been great for over a decade.

You definitely want to clean the welding area down to bare metal. None of that "I can weld through zinc crap". You want your welds to be clean and free from contaminants. It's not about welding up a nuclear anything. Contaminants can cause welds to fail, so you don't want anything in them.

Do it once and do it the right way!!!

I've done 4 sets of stiffeners, some mid, others the full frame. There are only a handful of things to actually care about. 1) clean base material. Get all the schmoo off, to bare metal. 2) get the stiffeners to fit tight with no gaps if possible. 3) a good weld to properly bond the stiffener to the frame means good welds with no defects. Primers and stuff aren't going to do anything for you, but you can use weld-tgrough primer if you want. 4) use body seam sealer to cover any gaps and to weather seal the stiffener from the frame. It's nasty stuff but it will do the job. 5) spray the finished, sealed stiffeners with undercoating or another robust spray.

Don't overthink this. It's a welding project on a 20-30 year old vehicle, not a space shuttle. Your tolerances are whatever you can bridge with a welder, and if you seal the stiffeners property with body seam sealer and paint you'll probably be better off than stock for corrosion anyway.

In addition to what everyone is saying... be aware you are welding 2 different pieces of metal with different thicknesses, quite different!!!

So keep the heat of your arc primarily on the thicker material and drag the puddle over to the thin unibody frame quicker than you keep it on the thick stuff, otherwise, you'll get lots of burn through. After you start welding, you'll catch on to just how long you can keep the puddle on the thinner material.

Black1990jeep said:

water can get inside the factory frame, it readily flows thru the front bumper end, which is open, then there are drain holes, and bolt holes in the factory frame. these will give access to water getting in between., Now one can seal every hole, seal every bolt head that sticks thru, and seal around the perimeter of every factory drain hole that lines up with the stiffener drain hole. But if there is any leakage between, that leakage will be trapped and cant be rinsed out effectivily.
Now you go wheeling and drag the stiffener over a rock, or come down hard and dent it. if the stiffener gets bent, the sealing maybe compromised, so water gets in, but without drains, how does it get out?

I just dont see trying to keep it water tight as an option, as there are too many ways for water to get in, and regular wheeling use will likely cause a sealant failure. it just takes one leak, and specially if the water or dust is salty and you will have trapped water, it wont drain as the drains are sealed it cant be flushed out.

thats my concern with sealing it, sealing it prevents flushing it out, and sealing wont be or wont remain perfect me thinks

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Gotcha.


Post up what weld settings you use. Probably shouldn’t try 17 volts and 120 wire feed speed.

Will let you know how it comes out It is a Miller Welder: Millermatic 212 autoset, Ar/CO2 0.03 wire. Maybe start welding this weekend. yeah we will be doing practice welds on same thickness materials.

I dont know about zinc. ive noticed what I thought was galvanized hair dust when I welded on mine.

I do not like welding galvanized bad juju

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That 212 is a nice machine id try it set at1/8" auto set but id likely turn wire speed down a fudge and maybe voltage.

Run the puddle on frame stifner mostly going side to kinda smearing it on the sheet metal frame. Be careful you will shoot some wire into the frame but youl fix it and figure it out.

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Black1990jeep said:

Will let you know how it comes out It is a Miller Welder: Millermatic 212 autoset, Ar/CO2 0.03 wire. Maybe start welding this weekend. yeah we will be doing practice welds on same thickness materials.

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So how did it go?

89Mock said:

So how did it go?

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First XJ is done with welding, it came out fairly well. friends son learned to weld and did the job with my help, this was his dads xj. We will do mine hopefully soon, got some other things going on first for my xj.

As this was his first weld project, we had to clean up some spots with grinder, but he didnt blow any big holes thru the body, nor start a big fire, and the welds although some spots are not pretty, the welds are secure,

What stiffeners did you go with? How was the fitment? Your buddy already had sliders?
Did he have to cut his sliders mounting legs that go to the unibody and take 1/8" out of em and re weld them back to the sliders? Id definitely weld the slider to the stiffeners, the other option is what? Bolt on? Nah.