ASE Certified Technician
Repairing rotted out floor pans from an old car is often a job done incorrectly. As Shop Manager at Motorheads Performance, I've recently encountered yet another a set of replacement front floor pans that were installed incorrectly, resulting in a repair which I'm sure was much larger than the original damage. Unfortunately, it is something I see time after time in our work with classic cars and trucks.
The latest set of front floor pans I've encountered for repair are on a 1969 Pontiac Firebird a customer had recently purchased. The previously "repaired" floor pans had been spot welded in place using an acetylene torch or a mig welder. Unfortunately, the spot welds were over six inches apart, with gaps up to a quarter inch between the base metal and the floor pan. The gaps of the floor pan to floor were filled with silicone caulking. The pans were also modified in an attempt to repair the rotted foot pans by sliding the pans forward toward the fire wall, thus leaving misalignment and clearance issues with the transmission support. The other problem was not only the pans themselves, but the floor was not properly trimmed and prepped for the installation. The excess rusted floor metal was not removed properly from the support structures, which caused improper seating of the new floor pans. This caused large gaps during the spot welding, which allowed leakage to occur. Dirt, dead leaves and other debris filled areas of original sheet metal that overlapped the new floor pans. Over time, the leakage caused further rusting of the original floor, as well as damage to the new pans from corrosion. The interior carpeting was destroyed as well.
Trial fit your new floor pans so that they drop into place with no gap or space between the new floor pan and the original floor sheet metal. There should be no overlap. Pans should be continuous welded all around the new seam. Do not spot weld, pop rivit or screw the new floor pans in place. Spot welding, pop riviting or screwing the pans into place will weaken the floor structure, especially on unibody vehicles. Normal driving will cause the floor pans to shift, tearing the spot welds, shearing the pop rivits and screws. Lastly, apply at least two coats of rust resistant primer and paint inside and on the underside. Lastly , a sealer is used to seal any gaps in the seams.
Correctly repairing floor pans may take a bit longer to do correctly, but will result in a repair job that will last a lot longer and not require further repairs chasing after yet more rust!.
ABOUT THE AUTHOR:
Guy L. Algar is co-owner of a classic car performance and restoration design shop in Leesville, Texas. Motorheads Performance specializes in repairs, maintenance, performance upgrades and restorative work on cars and trucks from the 1920’s through 1970’s. Guy is a Mechanical Engineer with over 25 years experience. He holds 5 ASE Certifications from the National Institute for Automotive Service Excellence and has been working on old cars and trucks for over 37 years.
