Thread: MII cross member advice on my frame

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Guys, I've decided I'm going to replace the hacked in MII stock cross member in my frame with a new fabricated style. This sounds pretty straight forward. However, I'm concerned that by the time I get the old one cut out, I'll find that whom ever installed it more than likely hacked up the frame pretty well too. So, I'm trying to decide if I would be better off purchasing a bolt in cross member or weld in one. I'm leaning towards a bolt in for a couple reasons. One, there will be more material to work with on it due to the sleeve that goes inside the frame rail. Two, I can bolt it on the frame and then repair my frame and have the correct geometry with out any guess work. My biggest concern with using a weld in style is that it's going to take a lot of work to get the frame rails fixed to get the correct geometry and have the joint be strong. Since I'll have a heavy engine and plan to add a supercharger later, I want it strong from the begining.

According to Speedway, their bolt in cross member is stronger than a weld in unit. It is also set up to be used without strud rods which is the style of control arms I have. So what are your guys's opinions on this? Here are some pics of my front cross member now.

what you have is stronger than any of the sheet metal xmembers unless it is a fatman . i have replaced 4 of them due to fatigue cracks.

Originally Posted by shine

what you have is stronger than any of the sheet metal xmembers unless it is a fatman . i have replaced 4 of them due to fatigue cracks.

Even with all the nice big gaps underneath and bad welds? What makes a Fatman better than say the speedway unit? From the research I've done, they're both made from 1/4" material.

Speedway, Heidts, and a number of other companies make some very nice crossmembers, they are made from either 10ga, 1/4" or 3/16" steel plate, not sheet metal.... The main part of the crossmember starts life as a piece of 10ga. wall 1 1/2" X3" or 4" rectangular tubing cut and trimmed to fit for some of the crossmembers, the rest start as steel plate and bent to the correct configuration. They are also jig welded, either MIG or TIG depending on your preference and your checkbook! The hats are also 10ga. steel or larger, and stamped out with a huge press. I've used many of them and have never had a problem. My experience with Fatman stuff was never very good....guess it depends on who you talk to. Personally, I prefer the weld in units and I always add a gusset or two as well as boxing the frame rails from the front to at least the transmission crossmember with 10 ga. steel. Any units I've ever seen that crack or fail have always ended up being installer error.....

fatmans are 5/16 wall tubing . if there is another out there i have not seen it . most others a made from 3/16 , in some cases less , flat plate welded together.
the original crossmember is stamped with a rolled edge for strength and also has an added plate where the lower a-arm bolts on . while the installation of his leaves something to be desired it could be saved with some clean up .
another option would be a fatman stub to replace the front frame section. i just did this on a 37 that had an older mll kit under it . it was the early version that kept the strut rods with the 1/2 plate mount so it fatigue cracked in numerous places .
tried to upload pics but they are pretty large.

I guess I don't see where 5/16" wall tubing is any sort of advantage, the crossmember is only as strong as the frame it's attached to and I don't see why anything this side of a semi would need a frame or crossmember that thick! Ya , the old stuff with the stamped steel arms and the strut rod aren't that great, but the op already made it clear he has the tubular a-arms that don't require a strut rod.... My thing has always been that the construction technique and detail is far more important then the mass and bulk of the material used!!! All of the crossmembers should have extra gussets to the lower a-arm attachment point, IMO one is not enough, but again, no reason to make that gusset any thicker then the structure it's welded to. I was around when Fatman was new, and their fitment and geometry was questionable at best. I'm sure they've improved over the years, but IMO they aren't the best unit on the market but do offer an acceptable product at a decent price....

Unfortunately, many of these IFS kits have been installed by folks less then qualified to do it, and many are lacking in the knowledge of basic fabrication techniques, but that's what the market wants so that's what the market gets!!!! I much prefer building with round tube, and seldom (if ever) use anything thicker then .083" wall and have never had any trouble. But a "first timer" using lightweight material would have fits trying to make it structurally sound! My point is, all of the MII suspension package manufacturers are playing in a very competitive market (price wise) and many have resorted to questionable materials (larger, thicker, bigger, etc.) as a selling point! But, then they also have to try to make their components "idiot proof" for the at home d-i-y guy who may or may not have the necessary expertise to do the build/install correctly..... As with many things involved in a build, there is seldom a clear cut winner in the "this is the best" product wars, and it comes down to preference and past experiences with a supplier......

You can definitely look at the pics of my frame and see what Dave is saying about the DIYers installing these. Now, like I said earlier, I'm no pro fabricator, but I do the best job I can. On this front end install I want it to be the best it can be, and I'll be doing it. I know I can get a new cross member set in where it needs to be. My biggest concern is how much of the frame is still there? You can see where they hacked a huge portion of the frame out and never put anything back in there. In my mind now this area is weaker now than what it was initially. I'm going to have a 750lb 354 Hemi, a 46rh trans, and some day at least a 671 on top of it. I don't want to have any issues later.

With all this said, I did think about buying new rails or a complete frame. That sounds like a novel idea, but the money is tight, and that much money will go farther if I fix my frame. (But those new frames look so sweet. LOL) We're expecting another kiddo this summer, and I'm going to be trying to buy a house within the next 2 years. So my plan is to get the remaining old cars and trucks I have running and at least drivable before we get to the house point. This car will be seeing the main part of the project funds. My 72 chevy is really close, and my other truck, well it can wait. My Vette runs and drives, just needs some roll cage changes, and maybe new wheels. Anyhow, this car will need lots of money thrown into it and I'm just trying to make smart choices here. It seems a lot of places are making MII cross members, but most of them don't look like they are as nice as others. Thanks for the help and info guys. Keep it comin. LOL

My suggestion on the '40 would be to get the car set and leveled, then install some bracing and cross pieces clamped to the frame rails so that things don't start jumping around when you remove the junk that is in there now!!! You might even want to consider some sort of fixture on the front of the rails to secure them and get everything square and level before the old crossmember is removed and the new installed! Measure, measure, measure!!!! I do see what you mean about the bolt in being a consideration....if there are enough of the original attachment points left on the rails that you will have valid reference points????

Originally Posted by Dave Severson

My suggestion on the '40 would be to get the car set and leveled, then install some bracing and cross pieces clamped to the frame rails so that things don't start jumping around when you remove the junk that is in there now!!! You might even want to consider some sort of fixture on the front of the rails to secure them and get everything square and level before the old crossmember is removed and the new installed! Measure, measure, measure!!!! I do see what you mean about the bolt in being a consideration....if there are enough of the original attachment points left on the rails that you will have valid reference points????

I was thinking of getting some 2x3 tubing and laying it under the car. Position the car at a good working height in the air, supported by stands. Put the 2x3 sticks under the car from front to back. I'll cut 2x3 up and position them under the car. Tack them to the frame. Probably have 4 on each side where I can. One in front of the front cross member and one behind it on either side for sure. I used to straighten semi frames for a living, and the semi frame racks are like this.

Yes on the point of will there be any reference points worth a hoot. Now I can fix the lower frame rail flanges, then re notch them for a new weld in cross member and gusset according. I'm just scared thinking that these guys cut it not once, but at least twice and you just can't see how much is missing yet. Granted the bolt in kit is more $$$. The bolt on kit has the extra flange on the upper half. This will help beef it up and give a place for more bracing and such.

Now that you guys see the front end work, the x member has had it's own share of hacking. My plan at the moment is to get a speedway tubular x member for it. I wasn't going to, but mine has been hacked, tacked, twisted to clear exhaust, and what ever. I really will be wasting my time I believe by repairing the old one. The tubular speedway one looks so nice, and it should gain some room for stuff being that it is tube construction.

i'm afraid you will find out there is very little of the original frame rail left .

the 37 i did this summer was so busted up that it was faster and much less work to just hack it off and replace it .

Shine, that looks very nice! Does this stub bolt right in the original frame rails just below where the front body mount area where the 2 half inch or so bolts are? That X member looks nice too. Does fatman sell them as a kit, or?

well that would be a case of overkill . the stub slips inside the frame and welds . the bolts are for my piece of mind. i make the xmember to allow more room for the overdrive .

Shine, do you have any more pics of the stub, and x member? What does the stub cost?

Wow holly cow! I called Fatman and they're high out of their minds! They want $1250 for the stub. After looking at it more, their stub is just 2"x3" 1/4" wall rectangle tube with the ends trimmed like stock rails. So basically I could do the same thing with 2x3 and a good MII cross member for literally half of that. Crazy stuff there.