Lower cowl patch from underneath, how I did it!

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vikingsandpintos

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7173 Mustang Supporter Member
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Location
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My Car
71 Base 6 cylinder, and 72 Base 351C
The dreaded lower cowl rust out... I have this info in my build thread, but thought I would do this thread with just the cowl repair

Mine was only bad on the passenger side, so I decided to replace just a portion of it. I didn't want to cut up the top cowl too, so this is what I did
 
I pulled the heater box, and changed the heater core while it was out, and patched a couple of holes in box. I also unbolted the dash structure to gain access to the area I needed to fix. I am putting a new American Autowire harness in the car, so I had most of the dash apart anyway.

I wire wheeled the cowl, to see what exactly needed to be cut out. I tried to cut as little as possible
 

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I bought a replacement cowl, marked and cut out what I needed to replace the bad section. I wish the aftermarket would sell just this area of cowl instead of having to buy the whole thing! At least they are available though, as I would guess sourcing a stock panel thats good is probably impossible.

Marked what I needed, and cut it out with a body saw
 

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Put new panel in place, and welded on. Being awkward position, and not being a pro welder, lol, I did it with a series of tack welds, like doing a quarter panel, ect. Once it looked like it was all welded, I turned off the garage lights, and used a flashlight to find any spots that weren't sealed. Touched up a couple of spots with the welder as needed. TIP.. When welding, especially when upside down or other odd positions, wear ear plugs. Cause nobody likes that sizzle in the ear when a little piece of hot splatter gets in there!
 

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Did a little grinding, then used brushable seam sealer everywhere just in case. As this is under the dash, and I'm not worried about making an invisible repair, I didn't spend a lot of effort to make it all smooth. Then a little paint over the sealer.

Note, although not pictured, I used the seam sealer on top of the repair as much as possible also. Couldn't get to the whole welded seam on the side towards the fender because of the top of the cowl, but did as much as I could reach. Between the weld, and the sealer, I'm confident this repair will outlive me!
 

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Next will be to put heater box, dash ect back in. But at least this repair is done! I know there are several threads on here about cowl repairs, I wanted to show how it can be done from the bottom, if the whole cowl doesn't need to be replaced. I was lucky that I only had 1 bad section, so this worked for me. I also had the interior taken apart anyway, and will be installing an American Autowire harness, so I was halfway there. If your car is whole, it will be more work. But, it can be done from the bottom, without having to pull or cut the upper cowl.

Hope this helps someone else out there that has a leaky, rusted lower cowl!
 
vikingsandpintos said:
Next will be to put heater box, dash ect back in. But at least this repair is done! I know there are several threads on here about cowl repairs, I wanted to show how it can be done from the bottom, if the whole cowl doesn't need to be replaced. I was lucky that I only had 1 bad section, so this worked for me. I also had the interior taken apart anyway, and will be installing an American Autowire harness, so I was halfway there. If your car is whole, it will be more work. But, it can be done from the bottom, without having to pull or cut the upper cowl.

Hope this helps someone else out there that has a leaky, rusted lower cowl!
Click to expand...
 
vikingsandpintos said:
Next will be to put heater box, dash ect back in. But at least this repair is done! I know there are several threads on here about cowl repairs, I wanted to show how it can be done from the bottom, if the whole cowl doesn't need to be replaced. I was lucky that I only had 1 bad section, so this worked for me. I also had the interior taken apart anyway, and will be installing an American Autowire harness, so I was halfway there. If your car is whole, it will be more work. But, it can be done from the bottom, without having to pull or cut the upper cowl.

Hope this helps someone else out there that has a leaky, rusted lower cowl!
Click to expand...
Looks great
 
vikingsandpintos said:
Put new panel in place, and welded on. Being awkward position, and not being a pro welder, lol, I did it with a series of tack welds, like doing a quarter panel, ect. Once it looked like it was all welded, I turned off the garage lights, and used a flashlight to find any spots that weren't sealed. Touched up a couple of spots with the welder as needed. TIP.. When welding, especially when upside down or other odd positions, wear ear plugs. Cause nobody likes that sizzle in the ear when a little piece of hot splatter gets in there!
Click to expand...
Good Job welding upside down
 
vikingsandpintos said:
Did a little grinding, then used brushable seam sealer everywhere just in case. As this is under the dash, and I'm not worried about making an invisible repair, I didn't spend a lot of effort to make it all smooth. Then a little paint over the sealer.

Note, although not pictured, I used the seam sealer on top of the repair as much as possible also. Couldn't get to the whole welded seam on the side towards the fender because of the top of the cowl, but did as much as I could reach. Between the weld, and the sealer, I'm confident this repair will outlive me!
Click to expand...
You do good work
 
I patched from the inside then used eternabond to cover everything on the cowl side.

Classic auto air so the vent isn’t used.

Eternabond is the permanent version of flex seal. It is used in mobile home roofing. 15yrs uv rating.
 

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