Was under my car today 79 cutlass bought the car about 1 month ago
noticed underneath behind the front seat area kind of under the rear seats a frame or channel runs across the bottom. Mine is pretty bad on the drivers side
wondering if this is cause for concern. I don’t think it’s structure but would like for you guys to chime in
and can this be repaired or anyone sell new Chanel’s Looks like it’s got a bolt so I’m assuming it’s made to come off ?
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First of all, your car doesn't have a "subframe". It's a full frame car. That rust is one of the reinforcing channels on the underside of the floorpan. To stiffen the floor pan, GM used those "hat section" stiffeners spot welded crosswise on the underside of the floor. The frame itself looks solid enough in the photos. I suspect that once you get into this, you will find a lot more body rust than you expected, unfortunately.

 

thanks for that
are those hat section replaceable? Looks like it’s bolted on the one side

 

The bolts are the body mounts that hold the body to the frame. Unfortunately these bolts are threaded into captive cage nuts that are buried inside those hat section reinforcements. You can pretty much guarantee that the nuts are rusted to the bolts and will break loose and spin if you try to remove the body bolts. That's life, but it means that replacement will be a lot more invasive than you think. You will need to remove the interior, cut out the rusty parts, weld in new parts, then reattach the bolts and body mount cushions. The reinforcement is available repro.

https://www.chicagomusclecarparts.co...w-78-88-g-body

 

Thank you. Much appreciated

 

Thirty plus years ago - early nineties - replaced the entire rear section of frame on a "Box" Malibu. 1980 to be exact. New england winters had rotted out the rear frame rails and bumper. And the car was barely ten years old. Was able to find a shop - this was circa '92, which installed new cage nuts, and supporting metal, on the body tub - which had been stripped down, and removed from the frame.

 

Rear frame rail rust on these cars is so common that there are repro rear frame rails available in the aftermarket.