Extreme body/frame rot

[Sigurd Jarlson]

So the body/frame under my rear seats has rusted to the point that one of the control arm brackets for the rear axle is no longer attached to the vehicle. It's still being held up into the underside of the car either by the weight of the car or by the shock absorber, but it's about an inch lower than where it was previously welded to the attachment point on the unibody.
If I can do some sort of a functional yet ugly fix, I might be tempted to try, but otherwise this car is destined for the crap yard.
I took a video of what is going on.

Any suggestions would be appreciated, but I honestly don't even know where to begin.

thanks

[Sigurd Jarlson]

Based on this thread, I guess this comes up often.
https://www.a-body.net/forums/showth...t=trailing+arm
That repair might be beyond the ability of my little mig welder and me....

[tlc1976]

Good luck. Hope you can take some time, clean out the rusted mess, and get a good plan of attack and fix it. It's not really that hard, just a lot of work. I've just got a cheap Century 130 mig welder too that I run flux core wire in. None of my welds have ever broken.

[tlc1976]

At work with a good connection and got to see your video. I've done this on a sedan and 2 wagons. On those, the side rail is there at the door bottom, it has many bends for rigidity. Even if the bottom part (rocker panel) is rusted out, the top is usually in good shape in my experience anyway. So you can get some good weld up there.

I've never owned an a-body coupe. You'd definitely have to remove the seatbelt and side panel and see what you've got to work with back there. I don't know what kind of structure you have to tie into on a coupe. You will also have to remove the side panel and seatbelt to get to the bolt strips that the axle bolts go through. That's going to be the most crucial place to tie into, so get a good solid weld onto those strips. Might want to use some of that good de-ruster stuff they make now. Then continue to build up a nice structurally sound box, and tie it into the side rail or whatever you've got there. I overlap and attach to the side rail at the inside, and across the top, so 2 places. Then if you've got anywhere you can put an additional strip to tie into the car and resist twisting, you'd be better off. This gives you both an axis and another point which fully constrains any movement. This isn't so easy on wagons without losing the back seat, so I didn't do it on those. Still never had any problems, but doing it on the sedan made me feel better.

If you do this well, the car will be more solid probably than it's been in years. And might as well do both sides, as the other side probably isn't far off. At the factory they only weld the trailing arm box to the floorpan skin, and the bottom of the rocker which is the first to rust out. Why they don't weld to the top of the rocker (or side rail) is beyond me, it's so much stronger there.

[Sigurd Jarlson]

What did you use for your repair stock? I don't have great access to many sources of scrap steel, so I'd probably get stuck buying the material they sell at Home Depot or Lowe's.

Thanks

[tlc1976]

To build the boxes I used scrap 11 gauge steel (1/8" thick) they had at work, left over from cutting out things on the plasma table. To patch the floorpan, I used the skin from a scrap washer, dryer, stove, etc.

Are there any sheetmetal fabrication factories around your area? Typically they have their scrap picked up for pennies a pound. Maybe they would sell you some. Or scrap metal dealers might have piles of it sorted and might let you buy a handful. Steel suppliers might even have drops of it that are too small to do much with so they might sell them to you cheaply, they'll just send it off to the scrapyard eventually too. I guess there's always the box stores, I've never bought metal from them before, it's probably very expensive.

Typically I start with cereal boxes, pizza boxes, etc. and figure out my shapes that way, then transfer them to the steel and cut them out. A saw or plasma cutter is nice but a 4 1/2" angle grinder with a cutoff wheel works fine too. I have a garage now, but at the time I had nothing but some wooden steps outside, so I bent my pieces with a sledgehammer over the corner of the steps or jacked them up onto 2x4 scraps.

By the way I'd check out the rear axle itself and see how it looks. If you need to replace it, do it now. I've heard of several a-owners having the coil spring perches (trays) rust out and break from the axle. Thankfully I've never had that problem, even on the rustbuckets I've had. I even use the spring perches to jack up the car on a regular basis. But once you weld up the trailing arm brackets this way, you won't be able to unbolt the rear axle. I've been driving since 1992 and have never had to remove the rear axle on any of my cars, so I never gave it a second thought, I just welded to those strips right over the bolts.

[Sigurd Jarlson]

I actually changed out the axle a few years ago because the coil spring trays on the original had rotted out.
Thanks for the tips on tracking some scrap steel.