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Cowl - Top Inner rust repair

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I'm watching this thread as I have a persistent leak at the firewall on the passengers side. The factory seam sealer in the seam where the bottom panel connects to the firewall is loose. I have dug it out and resealed the drivers side with good results. I can also see the big glob of black sealer by the fresh air intake and down that side. I need to remove that cover to see it better.

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Excellent thread here - wish I had found it a few months ago - I have the same leaking issue on a 1978 280Z - here is a picture with the cowl removed on the intake area - looks to me like the shroud that covers the intake vent is part of the frame - anyone seen something like this and can recommend an easy way to proceed forward to stop the leaking around this? Thanks!

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Edited by LinParkFL

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Look to my pictures above. You have to remove the paint with a wire brush, so you can see the spotwelds, and then drill them out. Then you can remove the cover that's over the intake vent and have more room to work. It's hard to reach on the area between the air intake tube and the firewall, but that's the most important spot. I used alot of patience, small screw drivers to scrape of dirt and a work light.

You also need to remove the wiper motor.

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I just want to share some info. That section of cowl covering the vent duct is solid on his 78(part of cowl) 75 and older had this section spot welded to the cowl and mounted from underneath(seperate piece) they used seam sealer for the mating joint.

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Thanks GraphiteZ - that is what I was afraid of - what are my options at this point? I'd prefer not to do any cutting if possible.

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Thanks GraphiteZ - that is what I was afraid of - what are my options at this point? I'd prefer not to do any cutting if possible.
If you drop down your blower motor housing you can seal it from the inside as a temp fix. It is most likely going to be rotted in this area,if you want to fix it properly you will have to cut it all out and weld in new metal and re-apply seam sealer around the duct tube. Do you have any welding skills? If not i would recommend getting it done at a fab shop. It is really easy to get in over your head working with thin metal. I am currently at this stage on my car right now,i had to cut the cowl on top to gain access to the duct tube. Edited by GraphiteZ

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I figured sealing it on the inside wouldn't really do me much good since the water would still be getting inside something it shouldn't. I did some welding back in shop class in school like 30 years ago (enjoyed it quite a bit actually) but haven't touched it again since. Any recommendations on a welding setup that I could use for a project like this - what are you using for your setup GraphiteZ?

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I have only been welding for a short time myself. I picked up a mig 135 from eastwood, great entry level machine. I recommend runing gas 75/25 argon/ co2 , flux core gasless wire is really crappy to use, deffinately on thin automotive sheet metal. The 135mig is $300 and a good size gas bottle will run from $50-100 depend on size. With some practice you will be ready to tackle this. If you have any other questions feel free to ask, I am no expert but I am willing to share my trials with you.

Edited by GraphiteZ

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There are some great solutions and work to solve this problem shown in this thread.

Here's a link to an earlier thread with some ideas and great pics. Member a7dz (Jim) did a remarkable job as well and has some great pics of his finished results.

https://www.classiczcars.com/forums/body-paint-s30/33769-fierwall-rust.html

I took some pics of this area as well when I drilled out the spot welds and removed the "rain cover" from the "top inner cowl panel". Most of these I've seen, seem to have been sealed rather haphazardly with a hit & miss method. It almost seems like the original intent was to create a few degrees of fall for the water to run away from the chimney to the drain. Not very well done or effective.

I had rust trapped in the seam between the top inner & outer cowl panels all the way to the hood latch support and broke those welds loose and removed the support so I could sandblast and repair the rusted areas. I welded it all together and coated it with a thick layer of DP90 epoxy primer and before the primer was cured, sealed everything with a two part epoxy flowing it over the area trying to create a small amount of fall as well. Because of events of the last few years, I still haven't finished prepping and painting this repair but it is solid and water tight. I decided to weld some nuts on the underside of the chimney cover and bolt it on, for easier access in the future.

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LinParkFL, if you read that thread I linked to, I mentioned using one of the adhesive panel bonding products. They have come a long way in recent years and I'm convinced that a cowl repair could be done quite effectively after cutting an access opening. We just need someone daring enough to try it and report back with pics.:D

It would be especially helpful for someone trying to avoid disassembly and heat from welding. It is necessary to cut an access opening somewhere on a '78.

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I welded new metal in for my cowl chimney repair and flowed some two part epoxy similar to the type shown in this link. It bonded permanently to the epoxy primer, creating a perfect, tougher than nails seal and I wouldn't want to be the guy trying to remove it. I wouldn't hesitate using these products or something similar on an area such as these cowl chimney leaks.

Master Bond Epoxy Systems for Metal Bonding | MasterBond.com

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I have found the source of my leak, see the cracked sealer in the photo. There is a gap between the firewall and cowl bottom of about 1/16" where the wiper motor sets. Although I have quite a bit of surface rust on the inside of the firewall panel the metal under the black bog looks good and solid. I need to finish the clean up and treat the rust and reseal. Overall it does not look as bad as what I expected.

There appears to be some writing and some embossed marks on the end of the fresh air tube. Anyone else noticed these?

I'm thinking about removing the tube by cutting the top out of the cowl area, drilling the spot welds holding the tub. Then re welding it all back together after it's all cleaned up.

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It's been weeks and I haven't seen wet floors since I repaired it ( see above ). @ jwtaylor, I'm borrowing your pic, to give my idea of what's the problem.

v58ga0.jpg

The red line indicates the lowest part of the cowl, and the road which the rain water needs to flow through, to both sides where the draines are.

The yellow indicates the main water blocking area, and also where the biggest rust occurs.

The green indicates the factory seal.

In my opinion the factory seal is to thick, creating a " dam " so the rain water can't go out easily, and it also lets some water remain standing infront of the seal, causing rust and eventually a leak..

What I did was scrape all the old seal off, in the entire cowl, so the surface is smooth ( allowing rain water to flow easily to the sides ), and applied a layer of rubber coating, which does 2 jobs all at once ( seal and help guide rainwater ).

Edited by bartsscooterservice

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I agree with you. In my case the amount of material in that area was up over the panel seam, just above the red line. I'm thinking that dam it created directed the water onto the top of the seam. The seam sealer had failed on both sides of the fresh air duct just past the black goop they used for the dam. In any case I have not found any rust on the bottom panel.

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FWIW, Eastwood offers a liquid sealer that has received a lot of good reviews from customers (a couple of whom have specifically mentioned using it to treat cowl areas). Positive comments about ease of use, coverage, and final appearance. Perhaps worth looking at - provided you're not dealing with corrosion to the point of needing to replace metal.

Eastwood Brush on Seam Sealer 30.4 fl.oz. - Item #51657ZP

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I have that very seam sealer to use when I am ready to reseal it. For now I have treated all the minor surface rust with some rust converter, need to let it dry a couple of days befor sealing and painting.

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I have found the source of my leak, see the cracked sealer in the photo. There is a gap between the firewall and cowl bottom of about 1/16" where the wiper motor sets. Although I have quite a bit of surface rust on the inside of the firewall panel the metal under the black bog looks good and solid. I need to finish the clean up and treat the rust and reseal. Overall it does not look as bad as what I expected.

There appears to be some writing and some embossed marks on the end of the fresh air tube. Anyone else noticed these?

I'm thinking about removing the tube by cutting the top out of the cowl area, drilling the spot welds holding the tub. Then re welding it all back together after it's all cleaned up.

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How were able to take this photo. I think there's a spar frame there, isn't there?

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