The first time I sat in my ‘69 Lincoln I was overwhelmed by the smell. It wasn’t just old-car smell. That I actually enjoy. There was a funky mustiness that I blame on Washington’s damp climate. Naturally I suspected the carpet and I decided that was going to be one of my first thing to replace. Bad smell or not, 50-year-old carpet is usually pretty gross anyway. It’s where everything collects and depending on the owner, it might not get regular cleaning. I was eager to banish the smell, but this is one of those painful layers of the onion that quite frankly had my eyes watering.
Holes Through the Floor Pans
I found rust for the rear floor pans first. This wasn’t just a surface problem, I had holes all the way though. These Mark III’s were designed for fancy rich people who didn’t want to be bothered with road or engine noise, so Lincoln installed all sorts of fibrous sound deadener (I think I read somewhere that it was 150-200 lbs. worth) throughout the car. The floor pans are no exception.
When our Flow Though Air drainage leaks, the spare tire shelf acts like the Continental Divide (get it?) half the water flows to the Atlantic Ocean and half to the Pacific Ocean–or in our case half to the trunk, and half to the passenger cabin. All that insulation then acts like a sponge, holding in that moisture for decades, unbeknownst the owner. This is why even if you hated my solution for the drain tubing–but your car has the potential to be out in the rain, or you take it through a car wash–prioritize that repair first otherwise you’re just working against yourself. You can always make it look prettier later.
Designed for Flow
What’s worse, is you’ll notice that these old cars had groves in certain parts of the floor pan that weren’t just structural. These channels flowed fluid during manufacturing and usually lead to a drain plug that was sealed at the end of the build. Essentially, these cars were designed to transport water to all the worst places if given the opportunity.
It looks like we have some repairs. If you were hoping to go online and order new floor pans already pre-formed to the factory specifications with all their fancy groves and cut outs–you must have forgotten that you own a Mark III (or Thunderbird) and nobody loves you. Don’t make the mistake of ordering floor pans for your year Continental–they are not the same car. It must say Continental MARK III. And it won’t, because they don’t exist. At least they didn’t when I started down this path.
Starting the Project
Now that we’ve cursed the internet yet again for wasting my time, here’s what you are going to need. You don’t necessarily need all of these, but the angle grinder with a wire wheel is probably the bare minimum for cleaning up the old rust and prepping the new metal. I didn’t know about those glorious Scotch-Brite pads at the time of this project, but I think it would have made my life much easier.
First thing’s first scrape out all the big stuff with your wire brush, and have a Shop-Vac handy. Once you clean up the big chunks, you can use the wire wheel to try and get rid of as much surface rust around the area as possible. You’ll be surprised how many holes are hiding because they’re filled with rust and crud (even from under the car). The goal is to expose enough of a perimeter that you don’t have any weak material and you can weld your new panel.
Looks much better now. Notice those little notches…yeah that’s where the leaky Flow Through Air drainage transported all the rainwater straight into your floor pans.
On to the welding part…
Good Ol’ Fashion American Steel
Congratulations! You are the proud owner of good old fashion American history. Back before we cared about emissions or noise…when we only charged batteries because we accidently left the headlights on…when cars were still made out of metal! If you are driving any glorious machine from the 1960’s or 70’s, be it Blue Oval, Bow Tie or Mopar, you are going to need 18-gauge, cold rolled carbon steel for any of your sheet metal work.
Ordering Metal
Unfortunately, places like Lowes or Home Depot are going to carry 16 gauge at the closest (which is thicker metal because metal gauge works the same as it does with shotgun shells, a 12 gauge is larger than a 20 gauge). Can you weld 16 gauge to 18 gauge metal? Yes. Should you? Avoid it if possible (unless this is the zombie apocalypse). Besides not stocking the right gauge of metal, most hardware stores aren’t going to have large enough sheets, and it’s probably overpriced.
If you are lucky enough to have access to a metal supplier nearby, then take your measurements and head down to the store. If you were like me, I went online. I recommend Online Metals 18 ga. (0.048″) Carbon Steel Sheet A1008 Cold Roll – Part #: 14695 They constantly have discount codes, and I appreciate how thoroughly they package the metal. You can also specify specific length cuts, so I needed a bunch of one-inch strips for a project and didn’t want to use an angle grinder for each one. I gave my measurements, and they showed up cut with nice clean edges.
The cost of metal is very dependent on the market and can change from week to week. Don’t expect this to be the price. Also, make sure you are ordering COLD ROLLED steel, not hot rolled, it has different properties that I am not going to get into here.
First Steps
Measure the approximate area that you plan on patching, length by width. I shouldn’t have to say this, but measure twice, cut once. Then when it comes time to cut your new panel, you have a few choices. 1: mark off your dimensions with a sharpie, and practice your skills with an angle grinder or cut off wheel. This can be challenging if you’re not used to these tools. I highly recommend clamping this sheet down to a workbench of stable surface because if you don’t, best case you hurt the metal, and worst case you cause yourself some serious harm. Angle grinders throw a lot of sparks so wear safety glasses! Ask the optometrist how much fun it is to dig metal slivers out of people’s eyes and you’ll never try and tough-guy it again.
I personally used my DeWalt angle grinder for almost all of my initial cutting, but there are other options that might be easier. If you plan on cutting a lot of sheet metal, something like this works pretty slick. If you draw a straight guideline and take it slow, metal shears can be more accurate if you are not very confident with an angle grinder. Again, choose the right tool for your purposes. Most of us are on a budget so I picked up a version similar to this from Harbor Freight. It is big, heavy and I wouldn’t want to lug it on a jobsite, but it has worked just fine for what I’ve needed. Metal Shears Harbor Freight
Tracing Your Metal to Cut The Floor Pan: Method 1
As the saying goes, there’s more than one way to skin a cat (though I can’t say that I’ve dabbled in that endeavor). When it comes to setting up your panel, there are a few different ways. Start by looking for a clean perimeter on your floor pan that hasn’t been rusted through. Cut a piece of metal to fit that perimeter. Lay your metal onto the spot. Trace the outline with a sharpie. Remove your panel, and then use your angle grinder/cut off wheel to cut out the perimeter that you have drawn. Many have done this with fine success.
Cutting the Metal WITH the Floor Pan: Method 2 (Better)
I am not a fan of the first method for a few reasons…. First you run the risk of not placing your panel back in the same position that you traced thinking it was “close enough.” But the big reason I don’t use this method, is it leaves too much room for error when you cut. Chances are you will cut a hole in your floor pan that isn’t correctly gapped for your project.
For butt welding, we need a tiny air gap between the edge of the old material, and the new (you shouldn’t ever overlap the metal with a new piece on top of the old. Just don’t do it). Ideally, we are looking for about .03 inches. Honestly, if you can fit a credit card (the thickness) between your metal and the cut floor pan, that’s great.
My preferred method to achieve this, is to lay your sheet metal into place, and then use sheet metal screws to secure it to the old rusty metal underneath (assuming it isn’t a gaping hole).
You could also use cleco fasteners for this. I don’t actually own any because I had a bunch of sheet metal screws laying around from an old roofing project, but I know the pros use clecos. Plus, they make everything look like some sort of mad scientist project.
Regardless of how you have fastened the sheet metal to your rusty floor pan, you are now ready to cut. If you are doing this with an angle grinder, try and find the narrowest cut-off disc you can find. Make sure it is .040 or thinner. If you go thicker, you will have a large gap that can cause problems.
Cutting
At some point I found a disc that was .035, but I don’t know where. These I picked up on Amazon for around $25 .040 Cutoff disc for 25. Trust me, unless you only have one panel to repair, you’re going to burn through a lot of cutoff wheels.
The first part of this cutting is going to go the same regardless. Make sure you are wearing safety glasses, and I encourage hearing protection. Pick a side. Any side. And start cutting. Slow and steady. Make sure you’re wearing your safety glasses and hearing protection. You are going to notice that cutting this is much easier than following a Sharpie line, because you can use the edge of your panel to guide your cutting disc along. Also, you are making the cut absolutely identical between the floor pan and the panel. Slick, right? If you are using a .040 cut off wheel, you are also creating a good air gap for your weld.
Once you have cut your first side, choose a side adjacent (next to) the cut side. Go ahead and cut this side out next. Again, take your time.
Next Decision
After this, you have some decisions to make regarding your air gap. After I cut out two sides, I made sure that both my patch panel and the floor pan were clean. I hit both edges with a wire wheel, because I’d already spent a decent amount of time prepping everything before cutting. You can use a wheel, or a Scotch-Brite pad. Vacuum up any contaminants and hit the spot with either a little Wax-degreaser paint prep like I pictured above, or even damp soapy rag. Make sure everything is dry and tack weld those freshly cut sides in place.
CAUTION: You must ground your welder before you weld anything. I highly encourage you to disconnect your car’s battery if it is hooked up. Find a suitable piece of bare metal on the body of the car that you can clamp your welder’s grounding line to. The closer to the weld, the better. I exposed bare metal on one of the uprights near the Flow Through Air’s drainage and hooked up there.
Refining Method 2
This is the method I used for this panel. However, I will let you in on a little secret if you’re trying to get a tighter air gap and you don’t have a thinner cut off wheel. Method 2: After I cut my two sides, I actually unscrewed my panel altogether. It was still being held down by the remains of the floor pan in the upper corner. I then butted the edge of my panel flush against my new cuts, essentially just shifting my panel about ⅛ inch into the cutout corner. I screwed the panel down again to the old metal and proceeded to cut out the remaining two edges of the floor pan.
At this point, your panel is attached to the rusty remnants of the old floor pan, but it’s not actually attached to anything and might fall through to your garage floor. That’s fine. Because now that everything is cut out, you’ve actually halved the air gap of your .040 cut off disc by making that minute shift. It is a little more awkward to hold into place. But I’ve learned that having a tighter gap on sheet metal makes welding much easier. From here, you are going to finagle your piece back into the cutout hole. Keep an even gap all the way around, and tack it into place just as you did the other way.
Welding it all Together
Now that your panel is tacked into place, you are ready to start welding. Aside from those ugly little overhead tack welds I performed for our drainage funnels, I actually haven’t touched a welder in about ten years. Let’s just say, the car wasn’t the only thing rusty in this garage!
More than a decade ago I completed a two-semester welding course at the University of Montana’s College of Technology. My primary goal was to hobby welding in my garage. I didn’t plan on using it to make money. I know how to weld. I am not a welder by profession. The course taught arc welding, but even on these big heavy boats from the 60’s, it’s pretty inapplicable because most of the steel isn’t that thick. I know the gist of TIG welding, and would love to improve, because you can do beautiful things with aluminum and stainless steel–but in the end I’m a hot glue gun welder, aka MIG welding.
Metal Inert Gas (MIG) Welding
If you’ve never MIG welded before, it is the easiest. The biggest key is knowing the gauge of material you are using and setting up your welder accordingly. For the Lincoln Handy Mig, you will find all of these settings on the inside panel where the wire spool feeds. Remember when I told you to get a shielding gas for your project? I hope you listened.
See right there! You should be running a 75% Argon 25% CO2 mixture for much better welds. Then go down to your material thickness and set the front at a HIGH-2 setting. The Handy Mig doesn’t have a lot of settings which can be good and bad, but it’ll work.
Next, they are recommending a 7 on wire speed, but I can tell you from experience that I dialed mine back to a little more than a 6. I don’t know if the machines have a variance or what, but listening is key. You want a nice smooth buzzing noise, not a bunch of popping. Mess with the wire speed accordingly, and once you’ve found something that works, it never hurts to mark it or write it down so if you bump your settings you can go back without trial and error. I’ve used my welder almost exclusively for welding 18-gauge sheet metal, so my settings stay put.
When it comes to wire thickness, stick to the .025 diameter stuff. Even though your bead will be thinner, thicker wire will just increase your chances of burning through.
If you are using a different type of welder, you’ll have to figure out the specifications. I’d recommend practicing on scrap material if this is your first crack at it.
Ventilation
If you haven’t done so already, make sure all your car doors are open so you have adequate ventilation. The welding process produces a lot of fumes that are toxic. I like to use a box fan to keep me cooler. It also helps scatter those fumes. If your car is anything like mine, you’ll have years of road grime underneath. I tried to clean most of that off once I figured out my cutout pattern, but I still ended up getting some bad smells from that gunk burning up from the heat of the welder.
Watch Your Heat
When it comes to welding sheet metal, you have to be very careful not to introduce too much heat all at once or you’ll warp the panels. Either run short beads of maybe an inch max or individual tack welds in a given location. Then weld on the opposite side of the panel. Make crisscrossing patterns like tightening the lug nuts on a wheel so you are spreading the heat evenly, throughout the panel. If you have a little air compressor, you can cool the piece down. If you notice you’re starting to burn through too fast on your welds, the metal is too hot. Otherwise, use your wire brush to continuously clean up your welds as you go. This allows your panel to cool down, and gives your welder a break so you don’t overwhelm the duty cycle.
Expensive welders have impressive duty cycles where you can weld consistently for great periods of times. Cheaper units like this Lincoln or Harbor Freight models need some time to recover between welds. Don’t overwork it. Weld a little bit, pause. Weld a little more, pause.
Completing Your Weld
It will take a while to completely weld your panel in place (and don’t forget to also weld shut the screw holes from earlier). Considering I hadn’t done this in a decade, I was fairly satisfied with my first go through on my panel. If you hate a section of weld, you can always grind it flat and try again. Considering this is about to get covered with seam sealer, paint, sound deadener, insulation, and carpet, I’m satisfied.
You might notice that I had to weld in a smaller 2-inch square where there was another hole to the right of the panel. I also had to use a hammer and block of wood to form the upper left-hand corner to a dip in the floor pan (not very clear in the picture).
Final Thoughts
One thing I will acknowledge…those oval shaped recesses in the original floor pan are not just for looks. They provide structural rigidity. If you notice your smooth panel seems to give a little if you stand on it, that’s why. I promise you won’t fall through. You won’t notice it once you have carpet in there. But if you have the tools at your disposal to add those groves, by all means go for it.
In Part II I will finish welding up the other holes and move into protecting everything.