47-55.1 Crack in the cross member

[hogfarm]

Finally got around to fixing the crack in my cross member. First picture is the crack, I put a couple little weld on it just to hold it until I could get it fixed.
Second pic it after grinding out the tack weld and pulling it all together, went right back to where it should have been.
Third pic is tacking in new support.
I never did get pictures of the completed project, but ground the welds and finished welding, it just got to hot and I forget

[Rickysnickers]

As a suggestion, you might think about welding a plate, fishplating, that crack so there's just more than a single weld holding it together. And yes, I see the plate under the crossmember as well.

[dsraven]

I'm with snickers on that one. smooth the weld out and weld a fish plate over the area. google what a fishplate should look like as there are many different theories on it. all the welders i have seen that fishplate a crack used a rectangle with the corners cut off and tapered and then they bolted or welded the long sides down the cut off edges but left the ends unwelded. they say it is for stress relief so the frame doesn't crack next to the fishplate. I would do both sides of the frame because if one side cracked then the other side is likely under the same type of stress so it may also need some help.
just a suggestion. it's your truck so you gotta do what you want, as long as it is safe to be on the road with everybody else's family.

[_Ogre]

good job pulling it back together! as others have mentioned, i'd plate it, otherwise it will crack again

[mr48chev]

Outside of the roads you have to drive on i'm wondering if metal fatigue caused that.

I'd be inclined to cut a plate that covered the whole corner of the crossmember with a hole for the bolt for the control arm to go through.

I'd be taking a hard look at and maybe replacing the strut rod bushings too. If the bushings are soft or loose that would let the control arm move.

Back a few years ago when you used the stock MII control arms with the aftermarket crossmember more often than not guys often heated and bent the strut rod to get it to a spot where they could weld the bracket to the frame and changed the geomentry of the control arm and strut' pivot points. The hole in the strut rod bracket should be Centered on line with the lower control arm bolt.

[hogfarm]

I agree fish plates or the idea mr48 has. I do not have a lift in my shop, I took the truck on a trailer to my friends shop to do the repairs. It was hurry up and get it done. now that the truck is back here I can fab up the parts, and when I take it down to have the mufflers redone, the guy there would be able to weld them in for me. getting little to old to be crawling round on the floor.

[hogfarm]

P.S. I know when it broke. I did not relize at the time but I had a jack under that corner and had jacked it up way to far to fit jack stand under frame. heard a boom and I thought the jack had slipped. It's all clear now

[_Ogre]

You should have been able to jack up your truck far enough to flip it on the roof without having anything break. Period. Jacking it up may have finished the break, but it was already broken by then.

[hogfarm]

Originally Posted by _Ogre

You should have been able to jack up your truck far enough to flip it on the roof without having anything break. Period. Jacking it up may have finished the break, but it was already broken by then.

I'm sure the crack was already there but the twisting from the jack finished it off, just glad it did not happen going down the road

[leegreen]

I'm with Mr48: metal fatigue caused that curved crack, even if the original weld followed that same curve. I'd look for reasons that the lower control arm would be bending the ends of the cross member front-back before going further to just weld it all stronger.

For further reinforcement, a plate that includes the hole and ties to the new lower plate on the cross member, as Mr48 shows, but taper it along the crossmember to avoid creating a stress point
Reweld those cold welds between the new lowerplate and cross member,
they are not critical welds but they are also the first welds any inspector looking under the truck will see.

[mr48chev]

They do sell a strut replacement that works a lot more like the backleg of a control arm and allows smoother movement up and down without binding.

[hogfarm]

Mr48
I need to take some more pictures tomorrow, explain to me strut?

[mr48chev]

I'm not sure that the 76 Mustang II front end that I have out in the pile of stuff still has the struts on it so I'll doodle up a drawing that I hope explains it.

Ford used the struts on a number of cars in the 60's and 70's and they tend to work pretty well unless someone dinks with them and changes thier geomentry.

The concept here is that the spot where the bushing that holds the strut in the back should be perfectly centered on the line though the center of the bolt that the control arm pivots on.

The issue is that back in the 80's a lot of guys used to heat and bend the strut so it in their opinion better lined up with the frame. That changed the geometry but from what I have read in the past it put the control arm in a bind more than anything else and I don't know if it would cause stress on that area. That may have another cause.

[leegreen]

this is an original MII cross member and subframe. the strut Mr48 is talking about is circled. I can see the bushing end of it in your second picture. If you can get pictures showing how it aligns with the lower control arm bolt it might help. Also check the bushing it in good shape

[dsraven]

the original MII suspensions that were using the original narrow stamped steel lower control arm from the car used a strut to locate the control arm in a fore to aft configuration. like the radius arm does on a for twin I beam truck. this is because the control arm has a narrow fottprint at the inner end, unlike the newer aftermarket MII setups that use a wider mount on the inner end. the rod that would bolt onto the control arm near the ball joint end would end at the frame behind the cross member on each side with a flexible style joint to allow the arm to fles some as the suspension moves up and down. google images will have a better explanation since a picture says a thousand words.
here is a quick diagram from an instruction sheet I found online that shows it.
https://www.classicperform.com/Instr...-48-Ford-2.htm

[mr48chev]

That Tubular strut rod with the bushing on the end is the original that I showed the Speedway knockoff of in post 11. Those worked pretty good and solved a problem when they came out.

I've got a buddy who's son owns one of the up and coming rod building shops in the PNW and is getting well known in the whole US who lost count of how many of the original MII front ends he put under cars and trucks in the 80's and 90's. Possibly starting in the 70's. He pretty well cleaned the wrecking yards in the area out of Pinto, Bobcat and MII front suspension setups in those days.

You could walk into the Ford dealership parts counter and buy a complete new crossmember for 111,-- around 1980.
The upper ball joint is the same one that is used in every Full size Ford from 1958 unil 1978 including Lincoln MKIV. I pointed that out to a couple of guys who said that the ball joints on the MII were too weak to have on hot rods.

[hogfarm]

I have been gone,but will get more pictures tomorrow

[hogfarm]

A few more pictures

[hogfarm]

And a couple more, I need to get the truck on a lift to weld the fish plates on. But headed to Alaska for a couple weeks then the truck is number 1 on my list

[mr48chev]

That sway bar looks like it is putting a lot of pressure on the the lower control arm pushing it back.

Is the bracket that holds the the sway bar bent? as smashed on a curb or rock or something? when the truck is raised up on a floor jack like that the sway bar link should be leaning towards the front at the at the top as the control arm drops and pulls it away from the sway bar. My guess is that that the mount for the sway bar is either pushed back along ways or has always been mounted wrong from the get go. I don't think anyone would have put it on that way as it is too far off. If it was mounted with the control arms hanging down originally it would push back on the control arm when weight was put on the suspension.

Is the rubber bushing on the back end of the strut rod in decent shape" the rock auto photo is what MII strut rod bushings look like when you take them out of the box.

It doesn't look like they heated and bent the strut rods unless they did it right at the control arm. You should be able to check to see if the center of the bushing where the rod goes through it is pretty well centered on the bolt that goes though the control arm pretty easisly .

In that one shot I can see what I think is the strut rod but can't tell anything about what is happening there.

[leegreen]

is the geometery right here? it looks like when the suspension compresses that strut will pull the lower control arm backwards

[mr48chev]

It would if that one was soft or worn out but it looks to be in good shape. I've got the struts and stock swaybar off a 76 out back and those bushings still look decent with probably 100K on them and they have been sitting out in the weather Since the late 80's. They don't tend to fail as much as the ones on the bigger Fords from that time frame. I used to replace those fairly regularly when I was doing front end work. That stock MII suspension is overbuilt and most likely stronger than a lot of the tube control arms with the Volarie ball joints that are on the market.

I'm still thinking that there is a badly bent sway bar bracket or possibly the strut on that side is bent from impact. If you run out in the garage or driveway and jack up any rear wheel drive rig with a front swaybar on it with a jack in the middle of the crossmember or on a two post lift with the tires hanging down the sway bar link is going to be pulled towards the front at the top not pushed to the back. Something is wrong there and the cause of the problem (s)

[hogfarm]

Good Morning Mr48.
I was able to work on the truck yesterday, a lot of rain, could not work outside.
1. the sway bar mounts are not bent. just picture angle,but it is shifted to the passenger side,I can adjust that. The picture "what is this" is shock bolt, it does not interfere with anything. I spend a couple hours under the truck since I don't have a lift but was able to make a pattern for the fish plates. And cut them out on the band saw, need to drill and as soon as I get back from Alaska I will go weld them in place

[hogfarm]

Forgot the picture

[mr48chev]

Good enough. Hopefully The Alaska trip is a fun one.