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1966 Ford Mustang - Project '66 - Complete Cowl Repair Procedures for '65-'68 MustangsOnce Again, We Tackle The Common Problem of Leaking Cowl Vents From the March, 2001 issue of Mustang Monthly By Mark Houlahan Photography by Mark Houlahan
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Our cowl is shown here properly... Our cowl is shown here properly repaired and basking in a coat of POR-15 rust-preventive paint. Using POR-15 is a sure way to prevent ever having to replace the cowl again. Cowl vent leaks are the Mustang owner's worst nightmare. Just about any vintage Mustang in need of restoration is going to need some sort of cowl panel restoration. Some cowls have minor leaks and can be patched, others need complete replacement panels (and we can thank the reproduction metal companies for making this step much easier), and the worst of them need complete replacement cowls. There is very little in the way of diagnosis-simply run some water into the cowl vent and see where it leaks from. On the worst cars, you can also see rust damage from under the dash-with the heater case and the driver-side fresh air vent removed. It's pretty much a given that the cowl will leak when you test it in this manner. The only things left to do is remove the top of the cowl area and survey the damage. 1 We're starting this project... 1 We're starting this project in the middle of a complete restoration, but if you're repairing only the cowl area, you will need to remove the windshield, the dashpad, the hood and its hinges, both front fenders, and the wiper arms for access to the cowl's spot welds. Clean away all old paint and seam sealer with a wire wheel. But why is the Mustang cowl design so prone to rust perforation? Well, it's a simple fact that the cowl of the early Mustang was poorly designed. The cowl, as it was welded together, had no access for proper paint application or rust inhibitors. Back then, metal wasn't dipped in EDP primer as it is commonly done now on modern cars; the protection came strictly from paint application after the body was assembled. The drainage of the cowl was poor, and any large items, such as leaves, twigs, and paper, could easily slip past the large cowl vent slots and dam up the drain areas-causing standing water to sit around the unprotected metal "top hats" of the cowl vent areas. Though the design changed for the '69 model, it's interesting to note that Ford used a similar design for the Fox-body Mustang from 1979-'93-a large cowl vent opening with a single air inlet on the passenger side. The drainage was improved, but the vent slots were plastic and smaller (allowing for paint application inside the cowl before the vent was attached), and the metal was EDP-coated as well. Project '66 needed cowls, of course, as do most '65-'68 northern cars. We didn't know what we would find-and except for looking under the dash (the interior was gutted for paint and body work), we didn't see any major rust perforation. We hoped cowl patch panels would complete our job efficiently. To be prepared, we ordered a left and a right cowl patch panel from The Paddock and sent them over to Classic Creations of Central Florida, so that when we arrived to shoot this article, they would be ready for assembly. Take a look.  2 Drill out the spot welds...  2 Drill out the spot welds that attach the rear fender apron extensions to the cowl. Be thorough to ensure you have found and drilled through all of the spot welds. Drill through only enough to separate the spot welds--you don't need to drill through completely.  3 Using a hammer and a chisel,...  3 Using a hammer and a chisel, separate the rear fender apron extensions from the cowl. We opted to purchase new extensions since ours had seen tough times throughout the years and were damaged upon removal.  4 Once the fender apron extensions...  4 Once the fender apron extensions are removed, you can start on the almost 200 spot welds that hold the cowl tank halves together. Classic Creations of Central Florida's Danny Gaydos prefers to start at the windshield opening, but it's your choice where to start.  5 To access the spot welds...  5 To access the spot welds across the front of the cowl, Gaydos stands in the empty engine compartment. You can reach them from the side of the car as well.  6-a After drilling out all...  6-a After drilling out all of the spot welds (look again because you probably missed one), use a hammer and a broad chisel to separate the top of the cowl from the base.  6-b Work your way completely...  6-b Work your way completely around the tank, searching for any missed spot welds.  7 With the cowl halves separated,...  7 With the cowl halves separated, the top half can be carefully lifted off and set aside. Again, make sure there are no hidden spot welds that were missed; otherwise, you will bend the tank top during removal, which will require more body repairs.  8-a This is most typical...  8-a This is most typical of a northern car and the condition of the cowls. The driver-side cowl hat has completely rusted away, causing separation between the hat and the cowl. The passenger side isn't much better, although it is still solidly connected to the cowl.  8-b We're lucky, though,...  8-b We're lucky, though, because patch panels will fix this problem. Anything worse and we would have had to scour salvage yards for a good cowl assembly.  9 After cleaning out the...  9 After cleaning out the leaves and other junk from around the wasted cowl hat, Gaydos proceeds to cut away the damaged metal, taking into consideration the size of the replacement patch.  10 Working on one side at...  10 Working on one side at a time allows for the most amount of strength to remain in the cowl area to prevent misalignment or warpage. The left-side cowl hat area is now free to be removed. We now have only good metal to weld to.  11 To prepare the good but...  11 To prepare the good but surface-rusty cowl area for the new patch, Gaydos uses a grinding wheel to clean the surface around the fresh cut for proper welding adhesion.  12 The new cowl hat patch...  12 The new cowl hat patch is clamped into place with several pairs of locking pliers. From the underside of the dash, the patch panel is scribed for cutting. There is no need to install the complete, as-stamped patch (requiring removal and careful measuring of the wiper pivots) if the area has solid metal.  13-a To more easily see the...  13-a To more easily see the scribe marks that were made, you can utilize a grease pencil, a crayon, or a marker to make the cut lines more visible.  13-b Cutting the extra metal...  13-b Cutting the extra metal off the patch can be accomplished with metal shears (as we are using here), a hacksaw, a reciprocating saw, a cutoff wheel, or other similar tool.  14 Though we plan to paint...  14 Though we plan to paint the complete underside of the dash with Eastwood's Corroless paint, Gaydos wanted to make sure our fresh, unprotected metal didn't begin to rust before we had a chance to paint it ourselves.  15 A few well-placed tack...  15 A few well-placed tack welds are made along the rearmost edge of the cowl patch to hold it in place against the cowl. This is performed to allow form-fitting the patch to the cowl.  16 With the rear lip of the...  16 With the rear lip of the cowl patch tacked in place, Gaydos uses a body hammer to tap the edge of the patch until it meets squarely with the original cowl metal. As the metal lines up, another small tack weld is made with the MIG welder until the patch is completely held in place by tack welds.  17 Now that the patch is...  17 Now that the patch is securely held, all of the locking pliers can be removed and the patch completely butt-welded into place. Take your time, and make sure all gaps are completely welded, because any pinholes could pose as potential leak points.  18 Once your welding is complete,...  18 Once your welding is complete, don't forget to clean up the welds with a grinding wheel. Grinding the welds cleans them for paint adhesion and allows you to inspect for thorough weld adhesion and penetration.  19 Our new cowl hat patch...  19 Our new cowl hat patch is just about complete on the driver side. Notice again how we avoided having to deal with the wiper pivot by cutting well below it. Of course, if your rust damage is higher up the cowl, you will have to cut accordingly.  20 Once the welds have cooled,...  20 Once the welds have cooled, a generous layer of rust-preventative paint is applied to the fresh repair area.  21 The final step to complete...  21 The final step to complete the cowl repair is to apply a high-quality seam sealer over the welds, around the spot weld of the hat assembly, and inside the hat at the spot weld seam. Simply brush on seam sealer wherever you think water intrusion could happen. Follow these same steps we just outlined for the passenger-side cowl, and you will have your cowl repaired in short order.  22 After removing the worst...  22 After removing the worst of the surface rust with a wire wheel, we used a POR-15 starter kit to further protect our cowl. POR-15 Metal Ready is used first to neutralize any remaining rust, then POR-15 black rust- preventative paint is brushed on to seal our cowl from any future rust problems.  23 The top half of our cowl...  23 The top half of our cowl had seen better days as well, with several rust holes along the front and sides of the cowl top. These would have to be repaired before welding the cowl top back into place.  24 Any areas that needed...  24 Any areas that needed to be repaired were cut away until there was good metal to weld to, then custom patches were formed to repair the areas. We used scraps of good metal from what we trimmed off the cowl hat patches.  25 Here is but one of several...  25 Here is but one of several custom repair patches that were made to our cowl top. Notice how well the new patch blends into the original cowl due to the butt-welding. Don't forget to drill or punch new holes for MIG-welding, if the patch is over an area to be welded.  26 After wire-wheeling the...  26 After wire-wheeling the underside of the cowl top, POR-15 Metal Ready is brushed on to neutralize the rust. Notice that the upper corner of the cowl in this photo was practically rebuilt with custom patches.  27 The underside of the cowl...  27 The underside of the cowl top is then sealed with POR-15 black rust-preventive paint. When brushing on the POR-15 in either the cowl area or on the cowl top, make sure that you don't get any of the POR-15 paint on the areas that will actually be welded together. Use weld through primer in these areas.  28 Lay the top of the cowl...  28 Lay the top of the cowl assembly in place and use a large drift, a line-up bar, or a tapered punch through the factory alignment holes to set the top correctly. Double-check critical areas, such as wiper pivot holes, shock tower brace holes, and so on. Clamp the cowl top securely with several locking pliers to prevent movement.  29 The cowl top is MIG-welded...  29 The cowl top is MIG-welded back to the main cowl in several locations to hold it in place without the requirement of the locking pliers. At this point, the remaining spot welds that were drilled out are now welded closed again.  30 Break out the grinder...  30 Break out the grinder again and clean up all the welds surrounding the cowl assembly. Ensure that the welds are strong and that you didn't miss any of the drilled spot welds.  31 New rear fender apron...  31 New rear fender apron extensions are welded into place over the gap between the cowl and the rear fender apron. The price of the new extensions is reasonable and makes for a quicker, better-looking repair.  32 Before the cowl can be...  32 Before the cowl can be sealed with brush-on seam sealer, several coats of rust preventive primer must be applied. You should never brush seam sealer onto bare metal, because the seam sealer will trap moisture against the bare metal. Any quality, high-solids paint will work well for this.  33 Using a disposable acid...  33 Using a disposable acid brush is the quickest way to brush the seam sealer into all the little seams and welds. Start at the base of the windshield and work your way around the cowl. Don't forget to brush seam sealer under the fender apron extension as well.  34 When brushing the seam...  34 When brushing the seam sealer across the front of the cowl, don't be afraid to apply a thick coat. The original factory sealer in this area was usually applied to the height of the lower cowl lip. Don't be too concerned about the shock tower brace mounting holes being covered with seam sealer--they can easily be found and the sealer can either be cut or dug out.
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 | We take a glimpse inside the how, what, why, and where of restoring a vintage Mustang |
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