Friday, December 17, 2010

Cowl Panel Replacement - Episode 1: The Ugly Truth

Have you ever heard the comment:  “If it was easy, everybody would be doing it”?  Well, consider cowl panel replacement in a 69-70 Mustang to be the poster child for that statement.  Exhaustive research across the far reaches of the internet as well as through the archives of all of the Mustang magazines will produce annoyingly little helpful information on tackling this project on a 69-70 body car.  The tricky thing here is that the pre-69 cars, while similar, do not require the same repair techniques as the 69-70 and the differences between the jobs is significant in many ways.  Perhaps most significantly, the 65-68 cars have no outer cowl enclosures in their structure, making access to all of the critical structural weld areas much easier.  On the surface, this may seem like no big deal, but when you carefully evaluate the repair in a 69-70 car, you will quickly note there is no pleasant “path to paradise” in the proper replacement  of the cowl assembly and a lot more work will be required than what the available 65-68 repair articles will show.  With that in mind, I intend to document the details in the process of cowl panel replacement on my 70 in hopes it may help others contemplating the same work on their cars.
Here goes:
To begin, I must reinforce how critical it is to avoid getting in a hurry when performing this replacement and to understand that there will likely be a large volume of tangent repairs that will have to be made to achieve a proper overall repair.  Trust me, once the original rusty, crusty cowl has been removed, the number of other areas that will demand attention will be magnified exponentially.  After many days of studying this job from every conceivable angle, I determined this single project, while apparently simple in concept, will likely take me the bulk of the winter to complete.  Secondly, do not spare any expense on acquiring the proper tools for this repair!  Three essential tools you absolutely must have to do this job are: a Blair Premium spot weld cutter (the rotabroach variety), Cleco fasteners (the high clamping force type), and a variety of vise-grip type welding clamps.  Of course, the usual complement of hammers, dollies, drifts, punches, angle grinders, chisels, MIG welder, Band-Aids, Oreo’s, barley pop, etc. will also be required as well.
One thing that proved very deceiving was the perceived “advantage” of having a cowl that is already welded together and e-coated.  On the surface, this gives the impression of a part that is “ready-to-bolt-in”, but the painful reality of this is that is the farthest from true.  First, the car was never built with a pre-assembled cowl because it was (and is) impossible to properly weld the inner cowl flanges on the 69-70 body.  Secondly, there is absolutely no seam sealer on any of the interior cowl seams and these areas simply cannot be left unsealed with any expectation of long-term durability.  Unfortunately, unless you have arms like Kate Moss (ewww) and can contort the rest of your body to the shape of an ampersand, the task of sealing an assembled cowl is a mess to say the very least.  Third, in order to install the panel as an assembly, you must remove the outer cowl enclosures whether you like it or not.
The flip side is to take apart your brand new, beautiful pre-assembled cowl and install it like you would a 65-68 cowl.  This was impossible for me to justify as I just couldn’t bring myself to violate such a nice part by hacking it apart, but for some it may be the easier option, albeit with more risk involved.  Besides, once I removed my old cowl, it was painfully obvious that a lot more work was required to get the whole works into proper shape, if for no other reason than to soothe my conscience when the job is done.
The following photos document the start of the removal process for the old cowl and a bit of information showing several points of interest along the way.  There will be several more “episodes” to follow.
Before even the first spot weld is drilled out, I marked the exact location of both upper fender mounting tabs so the new tabs could be placed in the exact same location as the originals.

I like to use a wire brush in a drill to run around every seam so it is easier to identify spot welds that require drilling.

Here's a look down the front edge of the cowl with many spot welds visible.  Once I have them all located, I give each one a good center punch and I'm ready to drill.

Removing the old cowl requires that the top is removed first, then the bottom.  Here I have all of the spot welds drilled through the upper panel and have separated the seam around the front and sides.

Here, the top panel is clearly separated from the lower panel.

With the original top panel removed, you can see the extent of damage to the original lower cowl.  Also note how little corrosion protection existed in this cavity.  The vast majority of the enclosure is actually bare metal!

With little more than a bit of overspray to protect the steel, it is no wonder these areas are so vulnerable to the elements.

Here is the driver's side panel.  Rusted through as well.

There is a lot to be said about the next two photos.  First, you can see the interior of the cowl end enclosures are no better protected from corrosion than the rest of the cowl enclosure.  Unless these end enclosures are removed, there is little hope of effectively cleaning and treating these areas properly and absolutely no possibility of properly welding in the cowl along the inner cowl ledges.  Also, a particularly disappointing discovery is that everywhere the factory seam sealer was applied is covered in rust.  And I do mean EVERYWHERE!

The spot weld locations from the top panel supply the blueprint for drilling out the lower cowl welds as well.  I center punched each weld a second time and removed each one with my Blair Premium spot weld cutter.  After a bit of careful prying with a heavy putty knife blade, the lower panel was lifted away cleanly........only to reveal more rusty flanges where the factory seam sealer was.
Once the lower cowl panel was removed, I removed the outer cowl enclosure panels.  Here is a look at the passenger's side cavity.  Notice how little overspray the actually is in this area.
The same can be said for the driver's side cavity as well.

Here is a look at the inside seam of the new cowl.  Notice anything missing?

Absolutely no seam sealer of any kind exists in the new cowl, even around the base of the "chimney" pipe.  I plan to use a paintable 2-part urethane seam sealer on every seam, but applying it is going to be a real trick.

Note the nicely e-coated surfaces inside the new cowl, but the lack of any seam sealer.

Of course, a test fit of the new cowl was a must.  As good as this may look here, the fit was actually quite lacking and I was able to identify MANY areas requiring attention in order to get the fit as good as possible.

Primary alignment of the new cowl is achieved by using two steel drifts in the firewall brace holes.  This keeps the panel properly aligned and makes repositioning quite easy.

Here, you can see how poorly the initial fit-up was on the passenger side.  The gap seen in the middle of the frame is approximately 3/8".

Fore-aft alignment of the panel was pretty good, but will improve with more flange work.
That's where I am for now.  I have started the tedious work of honing the fit of the panel and will document the many hours involved in removing rust, identifying and repairing hidden damage, and applying rust preventive coatings and seam sealer to the various areas of concern before the panel can be actually welded in.  Stay tuned for Episode 2!


  1. You're doing good, high quality work there Sven!
    You make good points about the pre-assembled cowls but I can't see any better way of sealing the seams than the way it is now. From prior research it doesn't appear that "weldable seam sealer" like they used on these cars in the factory is even available today so it appears that our only option is to seal after assembly anyway or just rely on the e-coat of the after-market sheet metal and seal from the outside. Looking forward to part 2.

  2. You make it look easy! Oreo's and Barley Pop are a very important tool. I prefer peanuts, pork rinds and barley pop. LOL

    Keep up the great work!

  3. I thought I was set when I bought the complete cowl assmembly (pre-assembled) and then I went to a test fit... OMG there was a 1/2 inch gap on one corner. I thought my car body was all twisted because surely the new piece would be right. I did measurements (dropped from frame to ground) and measured across-ways, upways, downways, sideways, inways, outways - you get the drift... Anyways, I ended up splitting my pre-assembled cowl assembly across the front and sides, sat it in place and welded it back together. I ended up settling for the e-coat as the best I could offer for protection but will be watching closely on how you do your work here.

    Your cowl, I'm sure you must have downloaded my photos as it looks exactly the same as mine insofar as rust goes... :)

  4. Alex,

    Thanks for the continued encouragement! I need it! Being in the automotive industry, I have managed to find "weld-thru" seam sealers still available and regularly used. However, all of them are designed to tolerate conventional spot welding and not the plug-welds we have to use on so much of our projects (*Sigh*). So it looks like sealing up after welding is the only practical solution. I have found a 2-part paintable urethane seam sealer that should be able tpo be used inside the cowl. I will report in detail once I reach that point. Take care!

  5. James,

    Tools make it tolerable, but easy it ain't! Camera tricks help too! LOL

    And I like peanuts and pork rinds too! But that just sooooooo...........SUMMER! LMAO!

  6. Mike, I recall the nightmare you had with your cowl replacement and was losing sleep over this job in hopes I would not end up in a repeat of your experience. Believe me, if Dynacorn offered the 69-70 cowl as a 2-piece, that's what I would have bought. But as you might expect, no cookie on that one. I mentioned to Alex above that I have found a 2-part paintable urethane seam sealer that has an extended mixing tube that looks like it will make sealing the internal seams do-able. I will document fully when I reach that point. Stay tuned!