Is it possible   to replace the floor pan and rails with engine and tranny still in place?   I'm  just thinking about all the welding that needs to take place.  All  the fuel and lines have been drained.

The frame rails are still ok and don't need replacement.  Its just that rust has eaten a lot of the passenger floor pan.

Should be okay. The fuel lines ride high in the tunnel, so doubt you’ll be cutting in that area . This is if you are only replacing rails that attach to floor 

Right, not the heavy duty frame rails.  Fortunately, I caught them before the rust got there.  I need to do some practicing with my mig welder on thin metal.  its an art like painting.

52 minutes ago, hls3073z said:

Right, not the heavy duty frame rails.  Fortunately, I caught them before the rust got there.  I need to do some practicing with my mig welder on thin metal.  its an art like painting.

Yes it can be. You can always use a piece of copper behind the weld seam to prevent blowing through. I have a couple of pieces of copper tubing hammered flat on one end into different shapes. The copper won't stick to the weld puddle

Interesting idea.  What holds the copper strip in place while you are welding on the other side?

I can see that I need to keep asking questions before I do anything.

You can use magnets with the copper.  Drill some holes in the epoxy and install magnets flush with one side using epoxy.

 

Or you can buy: https://www.eastwood.com/4-and-8-in-magnetic-copper-butt-weld-backer-set.html

 

 

Sometimes I can hold the backer with one hand and weld with the other. Sometimes I have a helper. The Eastwood backers are really interesting. I wonder how malleable they are?

I'm about to replace rails and pans. car is on a rotisserie. My question is, when removing them, does the frame need to have bracing welded in to keep the shape of the car intact?

A 280 has a stronger trans tunnel brace built in. A 240 might need bracing.

I would also recommend you remove the running gear from the car while it’s on the rotisserie too... that’s a lot of weight.

Just now, wheee! said:

A 280 has a stronger trans tunnel brace built in. A 240 might need bracing.

I would also recommend you remove the running gear from the car while it’s on the rotisserie too... that’s a lot of weight.

Yes, I'm removing everything, doing a full restoration. I was on Youtube and it didnt seem people were putting any cross bracing in, but I figured someone here would have a clue.

Car is empty except the suspension and wheels.

As you have already heard, work on small sections at a time, don’t take out both floor pans at once etc etc.