While most of us respect and admire our vintage Mustangs, make no mistake--they were not a well-made car. Classic Mustangs were not designed to become collectible cars that would be around in great numbers 30 years later. Truth is, Ford designed and built them to live reliably for 5-10 years, then be filtered into the used-car arena and the scrap pile. Funny thing happened to vintage Mustangs on the way to the salvage yard, however. Old Mustangs didn't fade away and die, they retained their immense popularity and entered the ranks of the collector-car marketplace. As a result, we've had to learn how to cope with the Mustang's basic design and assembly shortcomings. Probably the biggest design flaw in the early Mustangs is the cowl-vent assembly, which is the single, biggest reason for floorpan rust.
Known to Ford engineers as the "balloon" assembly, the Mustang's cowl-vent box was designed to rust and leak right from the start. In fact, there was a Ford Technical Service Bulletin (TSB) issued during 1965 that addressed leaking cowl vents, calling for little more than generous helpings of body sealer around the insides of the circular water dams (hats) at each end. For most Mustangs, especially those in damp climates, the Ford TSB was a short-term fix. These cowl-vent balloon assemblies were not protected internally, which means they were never primed and sealed, leaving raw steel exposed to the elements. Early in Mustang production, the steel was not even galvanized, which would have helped considerably. The top of the cowl was galvanized beginning in the middle of the '65 model year. The bottom, however, was never galvanized. Because vintage Mustangs were not "E"-coated (dipped) during assembly, most cowl-vent assemblies had a generous layer of internal surface rust their first year that could not be seen.
For most people, the dripping cowl vent was just an annoying little leak that dampened their shoes and socks en route to work. Most were unaware of the damage that was taking place beneath the carpet. This '67 Mustang project vehicle from the East Coast is a case in point. The floor was heavily damaged from soggy carpet by the time we discovered the rust-out underneath. We decided to split the cowl and bring everything up to date. We looked to Pro Products for the cowl-vent-repair assemblies, which yielded the "hats" that we needed to repair our mildly rusted cowl. Rebuilding a rusted cowl takes undying patience, because there are hundreds of spot welds to drill out and a number of brass welds to cut. Then comes the task of repairing the cowl-vent openings to where they are rust and leak proof. This entails proper sealing of the metal with a good self-etching primer/sealer, then the use of a permanent-type body sealer at the seams.