Rear subframe mount sheetmetal - plan of attack?

[theNomad]

As I deal with replacing floorpans I inevitably have more that comes up. It's no show car and never will be. I just want to fix what I can. 

Here is the driver side rear floorpan around the subframe mount structure. 

 

So how would the experienced deal with it? I don't forsee being able to fully strip the car to a shell and redo all the metal, new mounts etc at this time. 

Can I fix it enough to get by? Just leave it until I can do it?

 

I was thinking of cutting  the top sheet metal just around the bolt hole (not removing the entire sheet metal, clean as best I can, por15, then butt weld in a patch with a few spot welds to the under brace structure?

[02tradition]

Ive seen on some race cars literally take out the pressed in bolt, weld a thick piece of metal over the hole, drill a hole through that, and then use a longer hex head bolt all the way through. So they are loose and removeable. Makes it easier to reinstall a subframe too. Don’t know how structurally sound that is but if a couple racers ive seen use it that way it must be?????

[TobyB]

Given how far gone the top is, yeah, I think your plan to go in that way is good.

If it seems relatively solid from the top, I agree- a stouter top plate

welded to the tube that holds the stud would be a good long- term stop- gap.

I would leave the tube top open, just because...

 

If you find swiss cheese below, however, then maybe re- evaluate.  How do the rockers

look from below?

 

t

 

[theNomad]

They look good so far from below. I haven't wheeled it all clean though as I haven't dropped the subframe and disassembled everything. 

What gauge is recommended that ill still weld to the surrounding metal?

[thinksound_mike]

my car was similar. A leaky rear window gasket let water in and it ran down under the back seat and rotted the floors (before I got it). The mounting area was also rusted out on top but the rest of it was very sturdy. The bottom was fine as well. I ended up cutting out all of the rust and patching in 18g metal where the holes were. I then cut several patches that I fit together and placed over that area so it has a double layer of metal. I drilled holes in the top patch so I could plug weld the interior surface area of the patch and then welded all of the seams too. Was it overkill? I'm not sure. I do know that it's rock solid now. I went over the mounting holes with the large patches; I figured I could always drill them out if need be.

 

Not recommending you do it this way, just sharing how I did it. I'm not a pro. I just learned to weld and did this in my driveway. I've seen way worse online so i think i did alright. The car is a driver, not anything special. Hope this helps.

 

 

Edited July 24, 2018 by thinksound_mike

[theNomad]

thanks, what type of coating is that?

[thinksound_mike]

rustoleum. I used a brushable seam sealer over every weld to fill in any dimples, etc after grinding. Then I sprayed an etching primer with a top coat of rustoleum. I did my best to eye ball a mix similar to sahara. it wasn't really necessary since it's all cover up with sound deadening and carpet now.

[TobyB]

As to thickness, whatever's as stout as you can make form the shape well enough to do a good job.

 

The original metal was probably close to 20ga (measure to check me on this)

but if you can get 18 or even 16 to do it, it won't be enough weight to matter, 

and it'll be that much easier to weld...

 

...just how I do it,

t

 

[theNomad]

Well today was my first time behind the MIG gun learning how not to blow holes in the pans. I got the driver rear in and will grind later in the week, but its a day of progress so I'm pleased. The passenger side will have its challenges but I should be better as well. 

 

Heavier metal in this rear area will definitely help and it looks like the heavy structures may make it easier to zap some good welds in there. After more practice I should be confident enough to try it,

 

Edited July 25, 2018 by theNomad

[Hans]

Keep in mind that bolt location is critical to rear alignment.

[theNomad]

50 minutes ago, Hans said:

Keep in mind that bolt location is critical to rear alignment.

 Yes, I used the small subframe braces as guides for the pan positioning and will only remove as much metal as is needed for the rust repair, leaving the good sections spot welded in and just peeling away the bad. I figure if I support the rear body and ease some pressure off the subframe while supporting it also, it'll stay in the same place while I do the repair.

 

I hope I'll also get access to the structure to fill with rust prevention.

[TobyB]

If it was me, I'd leave access holes to the structure (most of it's open anyways) and after your paint is all done,

hose that thing full of

3m Rust Fighter or Waxoyl or similar. 

 

That stuff is absolutely fantastic for stopping rust you can't

get to in trapped box sections and seams...

 

t

 

[Hans]

I used Waxoyl 30 years ago and it is still there.

[Simeon]

1 hour ago, Hans said:

I used Waxoyl 30 years ago and it is still there.

 

The Waxoyl is still there but the steel disappeared 10 years ago. 

 

Just kidding, couldn’t resist  ?

[Hans]

Down Under humour. Have more respect for your fellow "colonial".

I don't know how it would fare under full Canadian winter driving, but for garage queen duty, it has lasted well. I used a garden sprayer. That and a lot of seam sealer.