Looking for some tips on inspecting floor and sub frame rott.I bought a 1990 Iroc last year for a project and it seems to be a lot worse than i thought. I was looking to replace the floor pans but concerned about the subframe. here is a pic of the driver side floor and 1 of the car. Anything i should be concerned about let me know i might have to part it out dont want to get in over my head. Alot of rust underneith

Welcome aboard.

Has this car spent many winters in MI road-salt?
This looks like the status quo for such vehicles.
The good side is that otherwise the body looks straight.

The term "sub-frame" originates in that there are separate
structures front & rear, that the suspension attaches to,
with the chassis structure being integrated into the body.
As opposed to mid-70's construction where the body was
totally separate from the frame/chassis.

So that being said, elevate the vehicle enough to do a
thorough inspection underneath. The rear sub-frame provides
the mounting points for the lca's (lower control arms), panhard,
spring tower, and rear bumper. The front sub-frame provides
the mounting points for the front-bumper, and front cross-member.
The engine and front suspension a-frames mount to the
cross-member. After you identify the sub-frames, rust damage
will be obvious. Whether it's significant enough to cause structural
concern is impossible to know at this point.

If there is structural degradation, some help is available in the form
of aftermarket sub-frame connectors, that tie the front/rear together.
Body flex is an inherent design issue for these f-bodies, and the
connectors are a pretty standard upgrade for serious performance
vehicles.

You'll find that the expertise available on this board, is exceeded
only by the number of gas-bags.

Good-luck, and happy wrenching.

The floors actually don't look too bad from what you're showing here. I've seen a LOT worse.

Check your pinch welds, subframe-to-floorpan joints, and subframe around the transmission crossmember. All the areas where road salt and other debris like to collect. If those are good, then you have a good car to work with and it is well worth restoring.

I agree that that is not very bad from what you have shown. Mine had actual holes in that area. Your best best as stated would be to jack up the car and take a long, thorough look underneath. Surface rust is not a big deal to fix, flaky rust is a bit harder, and holes can be a real project-killer and PITA to fix. Take a small screwdriver or scratch awl/icepick under the car with you. Any rust spots you see, poke them with screwdriver/awl and see if you poke through. If not, then you have solid metal underneath that you can work with.

Yes it has seen many winters, I will get under the car again today and get a few more pics of the sub frame. my concern is that it looks like it is swelling if that makes sence. Front and rear sub frame look to be intack with the floor i'll do some looking tonight. I have the tools to mig the floor in but it will be my first time so i would have to practice i also have a couple friends that can give me some pointers. I 've read some forum and articals i'm sure it will be a challenge i love challenges. Just need to make sure i can weld new floor pans to the sub frame. also need to be concerned about any twisting.

I have some minor holes in mine, not near the front and rear sub-frames but they are there. For now my plans are to get Alston Inner Rail SFC's, weld them in and when I can remove my interior for its overhaul, I will do the floor pans. I want the SFC's at least for the inner rail just to ensure the rust holes don't see any excessive twisting to further make my rust situation worse or even my sub frames. Cheap insurance until I can permanently fix it. Keep us posted. Maybe get tons of pictures for us to diagnose of the under-carriage.

Yes, lots of pics please. The "swelling" you describe is a normal part of the rusting process. As the rust penetrates deeper into the metal, the metal begins to separate into layers and these layers eventually flake off. Before the layers separate the metal will appear thicker or to swell up. Any spots that are "swollen" like that you will want to hitthose areas hard with a wire wheel chucked in a drill and get some rust converter/preventative on those areas.

If you've got access to a mig welder, then you're all set. Floorpans on these cars are great to practice on. Tackle the small holes/areas first till you get confident you're laying down good solid welds, then move onto the bigger areas.

here are a few more pics of inside i need to get the underneath tonight or tomorrow. Forgot had to take wife to dinner doh.

Mine is basically the same, but both sides and just under the front seats, not real real bad and okay enough to drive on with the alston sfc's installed temporarily until a proper time of removal. As I won't be driving in much but nice weather anyway.

i replaced the floor in my 82 z28 because the previous owner had let antifreeze sit on the floor after the heater core broke. He just sat the car rather than fixing it or cleaning it up. When I got it the hole in the floor was from the tranny hone to just infront of the front seat rear mounting studs. I got ahold of a quarter pan from a parts yard and cut out the old and welded in the new. I will say however her in tx we dont have to worry about the whole salt factory you guys do.. My point... anythig can be fixed if you want to invest the time and money.

Ircker90, all the advice above is great!!! And I'm sure that once you get started, if you have any problems along the way, just post them up and any of these guys can help you out!!! Start small and move your way up to the big areas of rust.

GOOD LUCK! p.s. please take pic's of your work, and post as you go along.

Had a similar problem on my Z. the drivers floor pan near your feet was rusted through, along with the front of the drivers rocker and the drivers front strut tower had some flaking on the bottom. strangly the pass side was just fine. had a rust free parts car with no title and had my buddy who runs a body shop put the patch peices in. drilled all the spot wellds on the strut tower and replaced it. all looks factory, and now its solid!