Removing sheet metal screws

[Slowpoke]

OT:
On a 1997 Chevy C1500 WT originally from Illinois, I need to remove 3 sheet metal screws from the driver's door sill to access the shift cable.
One head broke off, and 2 are cammed out.
WD40, Blaster, and vinegar have no effect on the frozen screws.
A Vicegrip used on the underside of the door sill on exposed screws has no effect.
The screws are hardened, and even a tight grip will not budge them. I even tried a cobalt drill bit to cut the head off, but they are too hard.
So much for Rust Belt vehicles.
Any ideas as how to remove them?
Thanks

 

[kcm.MN]

Might be time to consider a Dremel tool and diamond bits. A diamond disc will cut it easy. And a diamond burr will grind through the steel. Just be careful of the bit slipping off the fastener.

Check these out:
https://www.amazon.com/s?k=diamond+...amond+dremel+bit,aps,190&ref=nb_sb_noss_1

 

[MarkB_MI]

If you can get to the back side of them, you might be able to get a Vise Grip on the threaded portion. But, of course, if you could do that you wouldn't need to remove them in the first place. But if you can get the heads off, you can probably get the rest of the screws out. I'd probably use a carbide burr in a die grinder to take the heads off.

Heat can be a wonderful help in loosening rusted fasteners. But the area where you're working probably has a lot of rubber and plastic parts that can be damaged or set on fire with a torch. If you want to risk it, use your smallest brazing tip to apply heat directly to the screw head. It shouldn't take much heat to break a small screw loose.

 

[Ericp351]

If have head left- put screwdriver in place- hammer down and try. If no head- cut or chisel a slot- repeat above. If too mangled- work CCW with sharp
small chisel or punch. When you get too frustrated, turn chisel sideways and eliminate head.

 

[Charles in Aus.]

You might try a stick welder with a heavy rod and low amps . The object isn't to weld but to apply controlled heat in a very small area ; the screw head .
The screw will expand and compress the corrosion , once really cool it leaves a space that will help you to free it with some force and release fluid .

 

[Geo-TH,In]

Take a chisel and strike the head of the screw sideways. That should break it loose. I do it all the time when I have a screw rusted on a window AC.

 

[Mule Meat]

A good pneumatic die grinder with a cone bit cuts the heads off easily.

Be careful when you remove the bolts that holds the seat and watch the airbag module under it.

 

[Slowpoke]

Not much trouble with seat bolts but needed large pipe wrench initially for seatbelt hold down bolt.
Last screw is under it.

 

[Slowpoke]

Self driving screws are recessed in plastic sill plate.

 

[Slowpoke]

I finally had to use a low LP torch flame on the exposed underside of the screws. The screws were locked in the plastic and the heat softened it enough to release them.