Early-Mustang Cowl Repair

This is the curse of any 65-70 Mustang owner...the dreaded cowl vent leaks. The situation started way back in 1964 1/2 (read that April 1964), when the Mustang was first released. The cowl vent area was an area that wasn't primed OR painted because the cover was already welded to the vents as it came down the assembly line. Hence, the vent areas were just bare metal. And we all know what happens when you mix water + air + bare metal. You get rust. In the case of the cowls, that meant water leaking in onto your feet, and your rug. This also meant water sitting on the floor boards, which meant rotted floorboards, etc etc. Just an all out curse. Many a Mustang has been abandoned because of these darn things (In case you're not sure what the cowl area entails, check out the picture below of my cowl cover after it's removal).


Well, my Mustang wasn't going to be one of them. And, since I had put in a ton of work repairing my floorboards I wasn't about to let leaky cowls ruin them again. So, I came up with a plan of action. I took picture from inside the the cowl area with simply holding my digicam through the Vent holes, to see how much damage is already there.

The first thing I did was, after removing the hood, fenders, winshield wipers, was to open up the side of the cowl like a 'tomato can'. This way of doing things has been suggested in the past in articles by Mustang Monthly. I didn't count the the spotwelds i had to bore out, but must be more than hundred.

After making the tomato can cut with a cold chisel and a sledge (you can use a cutoff tool if you want). I was able to get a better look inside at what I was dealing with. It was not a pretty picture. Rust had eaten away all around the 'hat' that was supposed to keep rainwater out, as well as chewed holes thru the metal around the hat area. I had hoped to be able to do the Mustang Monthly repair, but the amount of rust looked too great to repair thru that small hole in the side of the cowl. So, the cover had to come off. Of course, to get the cover off, the windshield has to come out first. This is accomplished by removing all the chrome molding, then cutting thru the windshield gasket with a utility knife. I cut away the outside of the gasket, so I could push on the windshield from the inside & so it wouldn't fall thru the opening while I was messing with it. The picture below shows my car with the windshield out.

Once the windshield was out, I could get to work taking the cowl cover off. There's 2 fender apron to cowl area extension pieces of metal that have to come off before you can access the welds under there. These things are a pain to get off without destroying them, so you might want to purchase new ones after they're off. Finally, I was able to get to work removing the cowl cover. There are a whole lot of spot welds that have to come out to get the cover off. The picture below shows a bunch of the hood side spotwelds already drilled out.

How I dealt with the spot welds was like this: I got 2 seperate drill bits: 1 sharp 3/8 drill bit, and a 1/2 drill bit that I ground until it was almost flat, just barely had an arch on it. The idea here is to use the 3/8 to get a good hole started, then use the 1/2 to eat up the top layer of metal so you don't go all the way thru the bottom layer of metal. You could also buy a spot weld cutter, but they're kind of pricey and dull quickly. This way works just as well, maybe taking slightly longer. I went around and did all the 3/8 drilling first, then came back with the other bit. After drilling everything, there were still a couple that I had to seperate a bit with a chisel and/or my Ryobi rotary tool. Below is a good picture of a bunch of the windshield area spotwelds already drilled out and separated.

Finally, after drilling out a ton of spot welds, the cowl cover was off. The worst welds were the ones where the cowl cover connects to the bottom part of the cowl assembly. These are barely visible (at least on my car), and after drilling out all the spot welds I couldn't figure out what was holding the cover in place. After a bit I noticed them and got them all drilled out too. This is visible in the next picture. You can see 2 groups of spot weld drill outs. The bottom grouping is the hidden one. Also in this picture you can see how the drill bit method leaves a small indentation in the bottom layer of metal but if you're careful doesn't go thru it.

With the cover now off, the full extent of rust was visible. It was not a pretty sight. It's a bit hard to see in the next picture, but the driver's side was nothing but swiss cheese. The cowl area was also full of years worth of leaves and other debris, which hastened the rotting process.

The passenger's side wasn't quite as bad, but the hat was completely rusted off of it and it was also full of a ton of junk.


Before getting to the repairs, here's a couple more pictures of what you might find lurking in your own cowls.... First is the driver's side. Blurry, but you can see the terrible holes at the top end of the picture.

The passenger side wasn't much better. The missing, rusted away hat had let so much water into the heater box that it had rusted it completely useless.

If you look at the next 2 pictures in conjunction, you can see how far the rust had spread. The 'lines' in the metal in the next picture is the area directly under the grills on the cowl itself. My car was repainted at one time, and this repainted area is the only place there was no rust.



Well, now that we had all this rust we had to do something about it. You've got basically 3 options when it comes to fixing this area, once more than just the 'hats' are rusted out. You can buy a patch panel from one of the Mustang suppliers, make your own patch panel, or try to fill in the holes with some type of body filler. This last option is the worst of the 3. With big holes and rotted metal, chances are good that the filler wouldn't stay in place forever. Once it broke loose, you'd have water again.

That leaves you with either a repro patch panel or making your own. In my case, I made my own. This was for a few reasons:
1. My driver's side fresh air vent was rusted beyond use, so I would have needed a new one of these.
2. I wanted to create a situation where NO water could ever come thru the driver's side again, especially since this was the scene of the worst of my floor rust.
3. After dealing with the floorpan and toeboard repro panels, I didn't have a lot of faith in how good they would actually match up. At about $50 each, they're pretty pricey. Too pricey for ending up not using them, like what happened with my toeboard. Now, before I go any further, there's one thing to note here: If it's your passenger side cowl hat area that's rusted real bad with big holes, or if you want to have the fresh air vent in the driver's side, you would probably be better off purchasing one of the patch panels. You've got to have the fresh air intake for the heater, or else your defroster won't work properly. I suppose you could make your own patch and then cut out your own holes for 'hats', but that seems like more work than it's worth to me. So, anyway, onto the patch deal.
I went to my friendly neighborhood Lowe's and bought myself a large piece of 14guage weldable steel. Then I came back and cut out all the old, rotten metal. 2 things to watch here: make sure you don't cut into the wiring harness (there's a wire grommet holding the harness up near the cowl area) and, if at all possible, don't cut into the are where the wiper motor mounts or where the wiper arms are.
After I got all the rotten metal out, I used a block of wood and a rubber mallet to rough shape my patch panel into the shape I wanted. From there, I took it and clamped it to the bottom edge of the cowl assembly and tack welded it into place along the 'grill' side of the cowl area. Then, once I had it welded securely on the upper end of the cowl assembly, I literally used my rubber mallet to beat the metal into the shape of the cowl assembly. Once I had it beaten into shape, I bent down the corner, ran a light coat of primer over it, and did a water test to make sure it was going to drain properly. Water ran right off of it, perfectly. So, I welded all the way around. The following picture shows the patch welded into place all the way around.


The following 2 pictures are good side views showing how the panel shaped to the metal, and also how it's sloped so water runs out of it.


This picture here shows a close up of my 'continuous bead' weld. It's actually a combination of a whole bunch of small welds. The flux core mig welder eats up the really thin metal, especially in this cowl area where it was all suspect to begin with.


After finishing the driver's side, I turned my attention to the passenger's side. Luckily for me, the old metal hadn't been eaten away around the hat; only the hat itself was rusted out. So all I needed to do was create a new hat. How did I do that, you ask?

What I did was this: I measured my old hat, which was still sitting in the cowl area when I pulled the cover, from top to bottom. I cut myself a long strip of sheet metal the same width, adding about 1/2" an inch or so to make up for rotted metal. Then I took the long strip and 'rolled' it into the shape of a hat. I took the rolled, but unwelded strip, and stuck it in the hole in the cowl, so I could make sure that I had the right width. Once I was satisfied with the width, I put a spot weld on the new hat so I could mark it, then pulled it out of the hole and welded down the edge so I created one whole piece of metal, a new hat. Then I popped it back into the hole and welded it into place.


Once that was done, the rest of it was simple. I used a very thin layer of metal filler to smooth off the areas that I had been working, sanded it down, and primed everything. Then I added a epoxy topcoat; for the cowl hat itself I used a gloss black, as it seems to be the slickest for moving water. While the cowl cover is off is a good time to paint the underneath of the cowl so it matches whatever color your car is.

Finally, I put a layer of undercoating overtop of all of my work, and further secured all the edges with seam sealer, especially around the hat area. In addition to give to work the final perfect touch I decided to paint evrything inside with the nice capian blue topcoat. If this would have been done in 64, we would find leaking cowls like that...

The true test was when I sat there pouring a bunch of water down the area, and letting a bunch of water sit in the area overnite. No leaks!

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