crossmember reinforcement/more clearance mod

[Cresso]

I don't doubt that a flat crossmember will flex. How bout any flat stock crossmember failures?

(deja vu)


Notice that I've never disagreed with anything said here. What I'm asking for here is more than an educated guess based on what people expect flat stock to do. I'm asking for someone who ran a flat stock crossmember to show us how it failed. Flex does NOT equal failure. flex equals flex. Over a long period of time, flex will fatigue metal until it fails. What period of time is that? What is the mode of failure when it happens to a crossmember like this?

Anyone with answers or am I gonna get more spobi? =)

 

[RCP Phx]

My 20 old son is just starting to listen now too!Its a wonderful life.These arent guesses but real life design issues!

 

[vintagespeed]

Unbelievable this guy. No one has any idea because no one would build one like that. Hello? Why dont you whip one up & show us all the pics of how great it works. Talk about vibes.....and I wonder how many dents it's going to put in his hood? Any guesses on the number of rear ujoints he goes through?

 

[2xtreme]

I appologize if my previous post made so much trouble. I applogize, after doing a little looking at the photos I have of other cross members I would have bent each side of the cross member up (making a U channel). I thougth (I have not checked on mine) that the trans mount sits basically flush with the frame rails? Maybe I am wrong. I know that I have seen several pics of them and they are flush with the frame rails, maybe they did more work than what it looks like??

Michael

 

[Bent]

The failure of the flat stock crossmember would not be itself. The flex that it would allow dependant upon it's thickness. By thickness, I mean within the realm of reasonable definition. In other words, exclude 2" wide by 3" thick. I think you get my point since you are trying to limit hight. "Metal" by by defenition will flex and return to it's original shape within the limits of molecular structure. In this case, the crossmember is not the "weak link". That could be your frame rails over time, transmision or any other component that would rely on what was a ridgid structure. If you are looking ONLY for the failure to occur on the solid flat stock, you may have to replace alot of other things around it many times before that may ever happen. I'm as much for over kill as the next guy. But first I like to find out which way the barrel is pointed.

 

[Kejtar]

cool.... this is what I was looking for:
pic1
pic 2 Now I can start planning for my second project Maybe I'll have it ready for Moab?


Btw.... flex means extra travel so that your shafts, tcase and ujoints will be working overtime as you're going over bumps and rocks so even if the crossmember survives you're more then likely going to damage something else. Furthermore if you're going to have the middle of the crossmember flexing in and out I can already see it loosening nuts/bolts that support it as well as braking the nutzerts inside...

Kejtar

 

[RCP Phx]

Now Im confused,thats a stock crossmember????

 

[Cresso]

Whew, this is painful. I'm not disagreeing with anyone. I'm not saying a flat stock crossmember will work. I just want indisputable proof that it WON'T work. I haven't seen that yet. This is sorta like the guys on JU saying a Cherokee will fold in half if you take the doors out. I don't know that taking the doors out won't fold it, but I'd never say taking your doors out WILL fold it unless I've seen it happen. Please, no one take this personally.

 

[BrettM]

Whew, this is painful. I'm not disagreeing with anyone. I'm not saying a flat stock crossmember will work. I just want indisputable proof that it WON'T work. I haven't seen that yet. This is sorta like the guys on JU saying a Cherokee will fold in half if you take the doors out. I don't know that taking the doors out won't fold it, but I'd never say taking your doors out WILL fold it unless I've seen it happen. Please, no one take this personally.

That's like saying "will wood work for making control arms?" then after everyone says "NO!" asking "show me proof?"

No-one has done it because it would be stupid. You won't break the crossmember, but your drivetrain was meant to be held pretty much stationary (maybe a few 1/16ths movement in the motor and tranny mounts). If you start letting stuff flex around you WILL have major problems.

If you want to use flatbar, I would suggest at least an inch thick.

 

[XJZ]

"This is sorta like the guys on JU saying a Cherokee will fold in half if you take the doors out. I don't know that taking the doors out won't fold it, but I'd never say taking your doors out WILL fold it unless I've seen it happen."


Dude, you are the perfect exemplification of JU. But I like the irony.

 

[Goatman]

Alright, like Jim said, you won't get a testimony on someone's flat crossmember that failed because it's so obvious that it won't work that no one (at least around here) would build one. The reason you want it as flat as possible is for ground clearance, which also means that it may have to support a major part of the vehicle's weight at some point.......which means it needs to be built with some structure. So, whether you're satisfied with the answer or not......that's the answer. For reference sake, I have bent the sh!t out of a stock crossmember, bent it up in the middle nearly two inches and the t-case was banging on the floor.

BTW, if you only believe what you see, then you can only learn from experience. There isn't enough time in our lives to experience everything, so sometimes we just need to figure things out.

I see Kejtar posted links to my crossmember. It's very easy to make, and plenty strong enough. It's been on there for three to four years with plenty of hardcore use, and it hasn't bent yet. I don't think the bottom of the trans mount is flush with the bottom of the frame rails, it looks like it's lower by a little bit. You also want a little thickness in the crossmember so the trans mount studs are up inside the crossmember, or they'll get the crap beat out of them.

To make mine, I cut the bottom off of a stock crossmember, just below the seam line, with a cutting torch. Then a piece of flat 1/4" was attached, and you can see how it bends up a little on the ends. I did add some support along the edge on top to increase it's strength, and had to clearance for the front driveline.

Here's a link to pics again, the two of the crossmember are at the bottom: http://fototime.com/inv/DFCDB9A8BDAF591

 

[JnJ]

First off mine is flat, and the t-case does not hit the tranny tunnel. I started with 1/4"x6" flat stock, during fitting test I bolted that alone up. The weight of the drive train caused it to bow. Now I'm no genius, but even I could figure out this is bad, so I used some angle on the back and front side to make it good and stiff.
If you really want to see a flat stock crossmember fail, I think you'll have to do it yourself, I don't believe the folks here are foolish enough to try it.

 

[Kejtar]

I just want indisputable proof that it WON'T work.

Umm.... ok... lets put it this way: you have been given the "mechanical" reasons why this would be bad. If you want proof then I really do suggest you make one and then report on results after 3 months of use, 6 months of use and a year of use if you make it that far. Be prepared though to suffer the consequences of a domino effect failure of components: from potential pumkpin problems to unjoints, drive shaft, transfer case and tranny/engine (a flexing crossmember will make the engine constantly rotate). Keep in mind that your failure can even include a fan through the radiator if you flex enough!!

Kejtar

 

[Ted Z]

it may work....but the torque from the drivetrain and the extra weight of the drivetrain pushing down on it when ya hit a speed bump or pothole even, will make it useless very quickly. And the concensus of the group is standard fab "rules" you basically don't use flat for anything but mounting plates and gussets... same reason bridges are not just a flat piece of concrete or metal. in designing anything you must design with a "safety" factor in mind, keeping the item being designed 2-3 times stronger than it needs to be.

 

[TLange]

I don't have a digital camera or a photo to show you how I did mine. I'll try to explain it the best that I can.

I used 1x2 retanguar tubing, 1/8" wall. I welded two pieces side by side and flat. This gave a cross member that is 4" wide, 1" tall and goes from uni-frame rail to uni-frame rail. I then took two 6" long pieces and welded those to the ends of the cross member in such a way that it kind of looks like a TC lowering kit. These two short peices are cut at 45 degrees on the ends so the bolts that go into the uni-frame sit inside the tube, not exposing them to rocks. The ends of the cross member are cut 45 degree as well just to make it better and maybe help keep the corners from snagging on stuff. The tranny mount sits right on top of the crossmember. I have 1" holes cut through the bottom wall of the CM and 3/8" hole drilled through the top for the tranny mount, again, protecting the bolt heads from rocks. I also have the Mopar TC skid mounted to it.

The stock CM hangs down around 3" and the the tranny mount sits 1/4" below the uni-frame. My CM hangs down 2" and the tranny mount sit 1" below the uniframe. It gave me an extra inch of clearance and at the same time a 3/4" TC drop relieving driveline angles slightly.

Why did I use two 1x2 pieces instead of a single 1x4 piece? Two 1x2 pieces welded side by side is much stronger then a single 1x4 piece. You've got four vertical walls instead of two.

I've hit it hard several times and high centered on it a few with no damage. It's been on my Jeep for about 3 years.

 

[4ward]

Here's a few shots of mine.

Here you can see the initial construction:

A little farther along:

Finished (sort of):

As you can see, the driveshaft cutout was on the wrong side of the crossmember. I cut the other side out and welded that chunk into the incorrect hole. All I can say is this was one of those 2 am been drinkin and workin' on the jeep projects.

I ran straight across the frame rails, didn't allow for the 3/16" +- drop that the stock one allows for. It's nothing that can't be overcome with a shim One of these days, I'll actually make up a batch and sell them.

Sean

 

[Kejtar]

I like it!!!!!

 

[vintagespeed]

LOL, just flip the picture horizontally and it'll be great for your advertisements. Looks pretty good beef wise.

 

[Rev Den]

indisputable proof that it WON'T work.

OK....I have been holding off on posting on this, due to pride....but here it goes.

My buddy and I replaced the stock crossmember on his CJ-7 with a flat piece of 1/2" diamond plate. 2 weeks later we replaced it after getting cracks at every bolt hole, except the 2 bolts that broke off. Chalk this up to ignorance, and youth.

If the folkes on THIS board say it won't work, trust them. Chances are SOMEONE has tried it.

KnuckleDome (Name changed to protect the stupid)

 

[RNMedic]

okay Sean I am gonna add that to my wish list. My I need to learn how to weld.!!!!!