How to Repair Rusty Rocker Panelsby Russell Wood
When a car starts to rust, it's literally being eaten alive; if it gets bad enough, the panels need to be replaced. A common area to find rust are the rocker panels because of their proximity to the ground, and therefore salt and water damage. Fixing a rusty rocker panel involves removing the infected metal and replacing it with a sheet metal replacement, usually available at a restoration specialist.
Open the door of the vehicle and place the replacement rocker panel over the rusted rocker panel. This should fit fairly tightly over the panel, but not perfectly since it is designed to replace the panel. Mark the edges of the replacement rocker panel onto the sheet metal below using the permanent marker.
Remove the replacement rocker and cut out the rusted rocker using the angle grinder with the cut-off wheel attachment. Make sure to cut inside of your lines, as its easier to cut out more sheetmetal than to replace it.
Grind the edges of both the replacement rocker and the stock rocker using the angle grinder with the 80-grit sandpaper attachment, so that both surfaces are bare paint. This is going to give you a solid welding surface on both sides.
Place the replacement rocker panel into the hole in the rocker, and line it up on all sides. This may be difficult to do depending on the size of the rocker, so if you need to, clamp the sheet metal to the vehicle using the vice grips.
Tack weld the perimeter of the replacement rocker panel to the vehicle using the MIG welder. A tack weld is a quick, short weld where you hold the trigger for no longer than one second at a time. By doing tack welds around the perimeter of the replacement rocker, you will minimize any warping that could happen from the heat of the welder. Make sure to move your tack welds around the panel frequently to minimize heat.
Grind down the welds using the 80-grit sanding disc, and make sure the welds are smooth with the surface. The panel has now been repaired.