Subframe replacement - torsion bar mount/transmission

I need to replace the driver's side subsframe. This is in the area where the torsion bar is mounted and where the transmission crossmember is bolted. Basically, my torsion bar is rusted in place and I've noticed considerable weakness as part of trying to work it free. So, I think the best thing to do is to remove and replace that section.

I've already got the replacement section and it runs from the rocker panel area to the high point of the transmission tunnel. One mitigating factor is that this is a convertible so it has the torque boxes. The replacement section I have does not have torque boxes.

Where would you recommend I cut out the old frame and does anyone have any pointers on the easiest way to remove the rusted section give what I have to replace it?

Also, is the frame section just tacked along the outer edge of the frame to the floor pans? Or will there be welds I need to drill? I've not done this before and wanted to get some advice on my best

Fortunately, the other side had been fixed previously (although I've seen better jobs). So, I will only need to do one side.

Thanks for the help in advance!

Before doing the job support the car with jack stands all around that area so the car won't sag or move when removing the frame. (Even better would be removing the engine (less stress on the body) and getting the car higher so you can get under it.) Yes subframe is spot welded and will need to be drilled out. I also used an air chisel.

On the outside where it is attached to the rocker there are welds inside the frame that you can't see holding it to the rocker. When I did the job I removed part of the floor to get at this area. I only had to replace the part of the subframe that attached to the rocker. I left in most of the floor for support and after I replaced damaged part of the subframe I then cut out all the floor and replaced it.

I think I have some pictures but I will have to find them. I will try to post later.

Here is the problem

Here is the problem cut out. I also replaced the rotted metal on the rocker but I don't have a picture of it.

New piece ready to go in

Tacked in. Here you can see the rocker metal has also been replaced.

Tacked in pic. 2

Pic. 3

Remove floor pan. As you can see in the pictures I had jack stands everywhere, a floor jack under the K -frame and the repair area blocked up with wood.

Another pic.

Floor pan prepped and ready to be welded in. Drill all the holes where the subframe attaches to the floor and plug welded.

Another pic of the problem

One more

Wow! Those are very helpful. Thank you very much. I'm going to study them a little bit more to make sure I understand what all is going on.

FWIW, the floorpans had already previously been replaced on my convertible. So, I am planning to NOT have to cut them out. I think that may make it a little tougher to replace. But, it shouldn't be that big a deal.

Based on your pictures and experience (as best I can tell), I am thinking that I probably should cut out from even with the torque box across to an inch or 2 short of the mounting point for the tranny cross-member. That way I won't have to be as concerned about getting the bolt holes lined up. And, getting in behind the torque box will be tough. If it turns out I need to cut out more due to rust, I can do that as well after I remove the first section.

I'll make sure I support the car with jacks on either side of where I splice it in. Although, one good thing I have in my favor is that the engine and transmission are out as is the interior and lots of other weight. I'll still support it, though.

Again, thanks for the help. I'll probably be back with more questions.

Glad I could help. You're doing the job right. You just don't want to jump right in there until you think about it for awhile.