Everyone knows Corvette bodies are invulnerable to rust - but the same is not true for the chassis. The fully boxed side rails in 1968-1982 models impart significant strength to the chassis, but they are particularly susceptible to rust because water can get trapped inside. If the chassis has a rust problem, it normally manifests itself in the rear portion of the side rails first. Because the rot progresses from the inside out, a problem may not be apparent from visual inspection alone. Poke along the bottoms of the rear crossmember and side rails with a pick tool or tap these areas with a ball peen hammer to expose any weaknesses. If you discover rust-through the best solution is to replace the damaged sections with new reproduction pieces. For the side rails, this means cutting out the rotted section slightly beyond the damaged area and welding in new sections. For the strongest repair, weld-in an inner sleeve that bridges the seams between the new sections and the original frame.
Whether or not your chassis requires rust repair, you will want to strip and refinish it during a comprehensive restoration. There are various methods for removing paint, undercoating, rust and other surface contaminants – including abrasive blasting, chemical stripping and electro-chemical immersion. With electro-chemical immersion, the chassis is placed in a large vat of liquid and subjected to an electric current. The chemical bath and current together completely strip the chassis inside and out. This is the most thorough method of stripping, but it must be done by a specialty shop with the right equipment and requires that the inside of the chassis be coated as well as the outside to prevent future rust problems. Chemical stripping is effective - but not recommended - because it is very difficult to prevent the stripper from getting into the areas between overlapping metal. Abrasive blasting is the most popular stripping method because it’s relatively inexpensive and very effective. The coarse surface texture it leaves behind provides excellent grip for the new coatings you will apply, but it is important to thoroughly clean out all traces of the blast media to prevent it from clogging the chassis’ water drain holes.
For the ultimate in authenticity, refinish your chassis with the original asphalt-based paint; but, for maximum durability and corrosion protection, use a two-part epoxy paint or have it powder coated. For the best of both worlds, use epoxy primer and sealer undercoats with old-fashioned asphalt based topcoats.