The plan was to wire brush the rust off of the front end frame, paint it, and start putting things back together. This plan immediately hit several snags…
First, there were rust holes in the firewall behind the doubler plate – the black piece in the center just above the transmission tunnel. This is underneath the large heater box, and is an area that traps leaves and pine needles. I had to clean out a lot of gunk in this area when I started working on the car, so this wasn’t a major surprise. It wasn’t a large area – roughly 4” x 6” to get back to solid metal. So, cut out a piece of the doubler, cut out the rust-eaten area on the firewall, and weld in a patch.
Of course I didn’t cut out enough of the doubler. After fighting the edges of the patch for a while, I finally just cut out the whole bottom half of the doubler to get enough room to work on the patch. Started a new, larger patch, formed it to the curves of the firewall, and then welded it in place. This actually went quite a bit easier than I expected.
The next step was to weld the pieces of the doubler back together and then weld it back in place. Except that the doubler was now too narrow! After studying it for a while, I realized that I had just butted the pieces of the doubler together, resulting in the doubler being narrower by the width of the cutting disk for each cut I had made.
This wasn’t enough to really make a difference, and no one would ever notice it when everything was back together. But I would know it, and it would bug me for years. So, cut the doubler in half, mount the two pieces back in place so that everything fit and lined up, make a filler piece for the cut, and tack it in place. Then remove the doubler, weld it up and grind smooth.
Since water tends to get trapped in this area, I took advantage of the opportunity to prime and paint this area of the firewall and the doubler piece with two coats of paint. The next step was to liberally coat the firewall and the back of the doubler with seam sealer, and then position it in its original location. The doubler was originally spot welded. I had drilled out the spot welds, which left me with holes that I could plug weld. After grinding down the plug welds you couldn’t tell anything had been done.
The frame responded well to a wire brush on an angle grinder. Fortunately and unfortunately, the bottom of the car was covered with undercoating. 50 year old heavily applied asphaltic undercoating… When new, this protected the floor and contributed to the quiet Imperial experience.
When 50 years old it was a combination of missing, cracked, falling off in sheets, and stubbornly attached. Now, this undercoating was a good part of the reason the floor was still solid, so I could have left it in place. But the poor condition of the undercoating bothered me, so it had to go!
I had discovered that the best way to remove this undercoating was a heat gun and scraper. Hold the heat gun on a small area for a minute or so, scrape off the softened undercoating, and then move to the next small area. Keep in mind that the bottom of an Imperial is roughly the size of a football field…
Inspiration struck – make an arm to hold and position the heat gun! After raiding the scrap wood pile I had this arm which would hold the heat gun in whatever position was needed.
The routine was to crawl under the car, point the heat gun at the next patch of undercoating, and lay on my back for a minute while the undercoating softened. Then move the heat gun a few inches, scrap the softened spot, and wait for the next spot to soften. Over and over and over.
It took me a few months to actually get the whole thing done.
Of course, scraping doesn’t remove all of the residue. So the next step was to scrub down the bottom with Prep-Sol and a sponge or abrasive pad. Did I mention that the bottom of this car is roughly the size of a football field?
After finishing removing the undercoating, I still had surface rust on the frame and various areas of the floor. The obvious thing was to use the wirebrush on the angle grinder. But the angle grinder was far to heavy and awkward to use under the car.
Die grinders, on the other hand, are light and small. Another chance to buy tools! A few days later these showed up, along with Roloc adapters and a variety of abrasives.
Roloc is an absolutely great system. The 3M abrasive disks do a great job of surface prep. You go through quite a few of them covering this much area, but they are relatively inexpensive and much faster and easier than trying to do hand prep.
After a few more days of prep, the frame, firewall, and floor were ready for primer and paint.
Next: Shiny Bottom