Continuing the effort of replacing the floor pans. In Part 1, I talked through decisions about parts and methods. In Part 2, we removed the old pans. Today, we focus on prepping the new pans and getting them welded in.
|paint from below, p-side|
|p-side pan prep|
What's a "Plug Weld"?
A plug weld is performed by drilling a hole through one material, setting that on top of a second piece of material and welding the two pieces together through the hole. In our case, we are making 1/4" holes in the new flooring. The weld is formed by setting the MIG wire into the center of the plug hole, pulling the trigger to start forming a puddle and then extending the puddle into the floor after the puddle has started to grab into the frame rail. Before we can weld, we need to poke holes in the floor, but where? I tried 2 methods. I'll explain them next.
Option 1 - Paint and Measure
Once the frame rails are clean, you just can't help yourself. You just have to drop the new floor on there and admire how nice it looks. It looks so pretty. Looking at the passenger-side pan sitting there, I wanted an easy way to spot the holes. I fiddled with the pan to make sure it was exactly where I wanted it and then set some tool boxes on top so it held still and firm on the rails. Then, I grabbed a can of white spray paint, slid underneath and spray-painted the edges of the frame rails where they met the underside of the new pan. When I lifted the pan off the rails, there were clear white lines showing where the frame rails were. I ran blue tape along those edges and marked drill holes every inch or so with a sharpie. The p-side prep picture on the right shows what the prepared pan looked like.
Option 2 - Use Old Flooring
|using old floor, d-side|
Drill Baby Drill
Regardless of which method you choose, drilling the plug holes is a two-step process. First you drill a pilot hole and then you drill out to 1/4". I suppose a step-bit would work so that would be only one drill effort. Similar to cutting out the spot welds, this is time consuming. I understand why British Auto Works (and probably most other shops) reduce costs by seam welding the outer edges. For that reason, I drilled plug welds into the floor to correspond to the inner frame rails, and only a few around the outer edge of the p-side pan. My paint-from-below method worked pretty well, though my alignment slipped a little bit and I had a few holes that didn't align with the rail.
On the driver (left) side, I chose to plug weld the whole thing, so that meant more drilling on that pan. The holes I produced with Option 2 were an exact match. They aligned on the rails perfectly. Unfortunately, the holes that cut all the way through the frame rail were now completely exposed as well. The drilling out of a single pan took me 2-3 hours and overall there really wasn't that much of a difference in time between the two sides, even though there were far fewer holes on the p-side. That doesn't math-out logically, but that's what happened. The all-in time at this point is over 14 hours and no pans are welded in yet.
During the actual weld-in, we had setbacks, of course, like some burn-through of the pan when we novices tried to run a bead, or small fires from grease or paint catching fire from the welding. Not to worry, though, they were small enough to blow out. Still, the decision to weld on the driveway rather than the standard low-ceiling garage turned out to be a good idea. We tested a few of the welds just for curiosity sake by banging on them with a hammer and trying to separate the panel with pressure from below. No dice.
That's it for today. My final steps are seam-sealing the floor edges, and getting some paint or undercoating on the steel pans. That work may not be interesting enough to warrant a post. After that's done, I am going to focus on getting the fuel system and master cylinders re-installed. Expect posts on those efforts soon. As always, thanks for following along.