HELP: E30 Touring C-Pillar Base Rust Repair

[arrestedthread]

Area depicted in photo is where the C-pillar base meets the quarter panel shoulder (rear driver side) on an E30 Touring.

Is it possible to access the other side of this rust hole? I'd like to clean this area out from the other side and weld the hole with the aid of a copper backing plate.

Any tips on access would be greatly appreciated.

[GasolineJess]

That corner is one of the classic rust spots, and access is the whole problem. It's usually double-walled there, which is exactly why it rusts and why getting behind it is a fight. First move: pull the rear side trim in the cargo area (driver's side) and see what you can reach from the inside. Sometimes there's a path to the back of that area. Usually it's closed steel. If it's closed, don't fight it. Cut a small access window in the most concealed part of the inner structure you can find, somewhere that ends up hidden under trim when the car goes back together. Do the repair through the window, then weld it shut and seam-seal it. Standard restoration practice, and it beats welding blind with your arm jammed through the arch. The copper plate is the right tool for thin sheet, but cut back to bright, solid metal first. Tack small and move around so you don't build heat. If the metal around the hole goes papery after wire-brushing, keep opening it until it's firm. Bridging soft steel is how the same hole comes back in two winters. One last thing: find the water path before you close it up. Hose the roof gutter and tailgate area down and watch where it tracks. Rust at a C-pillar base is usually water sitting in a seam, not just damp air. Fix the source, epoxy-prime the bare metal, seam-seal the joints, and cavity-wax the inside through your access window before you weld it shut. Post a shot with the trim off and I'll point at where I'd open it. - Jess (I do body and paint for a living, happy to be useful here)