Jim Smart
January 1, 1998

Step By Step

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The cowl-vent cap is fastened to the cowl-vent assembly with seemingly hundreds of factory spot welds that must be drilled out with the Eastwood Spot Weld Cutter. Once all of the welds are drilled out, there are braised joints in the corners that must be carefully severed with an air chisel. Then the cowl-vent cap lifts off, as shown.
With the cowl-vent cap removed, we can clearly see why Mustangs leak and floorpans rust. This is a Mustang that has been chemically dipped with all of its rust removed. What's left here are holes in the cowl-vent dam (the hat) where moisture was trapped between the dam and the sealer. Keep in mind that none of this was primered in the first place.
Pro Products offers two solutions in one product. The Pro Products cowl-vent repair panel enables you to completely replace either end of the cowl-vent assembly if rust-out is severe. If only the dam is rusted through, you can drill out the spot welds on the new repair panel and use only the dam for the repair.
If only the dam needs replacement, use Eastwood's spot-weld cutter to cut the welds on the old and rusted dam. Do the same thing with the Pro Products cowl-vent repair panel, using only the new dam.
Our project vehicle suffered from a missing windshield-wiper pivot nut plate. This is the best time to replace the missing nut plate and to do any repairs necessary inside.
Eastwood's Corroless fetches about $19 for a spray can such as this. But it is the best corrosion protection available for areas with high-rust potential. One can will cover the entire cowl. Spray the coats thinly and lightly, working your way up to complete coverage. Allow complete drying before work continues.
When the Eastwood Corroless primer has cured, we're ready for assembly. Weld the new Pro Products dams in place using the spot-weld holes already there.
With our dams welded in place, we're ready for a high-quality body sealer designed to seal water out. The best sealer for the mission is 3M's Heavy Drip-Chek Sealer (PN 51135-08531). This is a super-tough, waterproof sealer that dries hard, yet flexible. It is excellent for drip rails, cowl-vent-dam seams, and just about anywhere water needs to be kept out.
When the 3M sealer has completely cured, it needs a generous coating of Eastwood's Corroless. Once the Corroless has cured, ScotchBrite the surface, then apply body color to the entire inside of the cowl.
The inside of the cowl vent should be painted with the body color. Here we're using Plasti-Kote spray touch-up paint with antirust properties. Duplicolor works just as well in this application.
Our completed Pro Products water-dam installation is sealed, primed, and painted. No one will ever see it. Its effects will be most noted, however, when it rains.
Before you install the cowl cap, it is a good idea to lay a plastic bag across the bottom of the cowl to protect your body color from any primer overspray externally. Position the bags where you can pull them through the vent openings when all external bodywork is complete.
Spray weld-through primer along the contact surfaces of the cowl cap before installation, then lay the cowl-vent cap in place, as shown. Line up the spot-weld holes, as shown, ensuring perfect alignment.
Ford makes the assembly process easier. Perfect alignment comes from installing bolts in the jig pin holes originally used during body assembly. Get everything lined up, and crank down the bolts. Use C-clamps to bring the halves flush.
Clamp the cowl cap in place and rosette-weld using the spot-weld holes created when the spot welds were cut during removal. We're using Eastwood's Lincoln Mig-Pak 10 welder that runs on ordinary household current.
Eastwood's Mig-Pak 10 welder makes short work of a sheetmetal installation. We welded this entire cowl-vent assembly in two hours.
A small punch makes an excellent jig pin for installation of the gussets between the cowl-vent cap and the inner fenders. Be certain that the spot welds line up at the cowl-vent cap and the inner fender, coupled with the use of the jig pin. Then weld the gusset.
With all of the welding completed, grind the welds flush for a smooth surface. Plenty of grinding should be expected here.
Plastic bags positioned within the cowl, barely visible, protect the surface underneath. When all bodywork and painting is complete, we have a perfect surface inside.
The completed cowl-vent repair is ready for sanding, priming, and body sealer. The factory piled plenty of body sealer at the ends, and you should too. Use the 3M Drip-Chek Sealer at the seams prior to body sealer. Apply a thin film of Drip-Chek over the welds at the windshield.

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.