Such is the story in this post – although I think for once I actually got off pretty cheap. Last summer, I had the engine out of the truck, and since many of the lines, hoses & wires were already disconnected, I figured it would be a good time to replace the deteriorating firewall pad.
The firewall pad on my truck was literally falling apart. I think that this is especially noticeable in the open cab, since the pad is pretty much at eye level to anyone standing on the ground looking into the truck. In fairness to the manufacturer, it is only made of cardboard. I’m sure lasting 75 years was never even dreamed of as a requirement by the original engineers.
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The first thing to do was to locate a suitable material for the replacement. This proved difficult at first, since I kept searching for “cardboard”. I finally learned that cardboard tends to be the multi-layer corrugated stuff used for boxes, which is not what I needed. I realized, that what I should be looking for was chipboard, which is much like the material found in the covers of hard-cover books.
The stuff used in the truck appeared to be 1/8” thick, with a corrugated cardboard backing. The only chipboard I could find locally, in a length and width that would work, was 1/16”, so I figured I could maybe just take two pieces, bend them, and glue them together to get the 1/8” thickness. This actually worked out well, since glue line stiffened the pad and helped keep the bends at the correct angle.
I bought three sheets for just under $4 a sheet. I used one as an initial pattern. I trace the holes and creases from the original on to the pattern, then installed it in the truck, and made any necessary adjustments.
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Next, the first sheet was trimmed based on the pattern. I creased the chipboard with a piece of plastic on the bend lines. I found also, that slightly wetting the bend line helps to keep the surface from tearing during the bend. Once the first piece was bent, a second piece was bent and glued to the first piece using contact cement.
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I found some split rivets from McMaster-Carr, that were pretty close to the originals. The only difference is that the heads were rounded, however a couple of passes with a file and they were flat like the originals. Holes were punched in the chipboard, the flap interface was glued with contact cement, and the rivets were installed using a washer to help keep them from tearing through the chipboard.
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Speaking of holes, there are a number of different sized and shaped holes in the pad. I did not have any of the punches required for these sizes, so I cobbled some up from scraps of tubing, electrical conduit and pipe that I had lying around. To make a punch, you just hit the end with a countersink, then finish the edge with some 600 grit sandpaper. Stainless tubing works best, as it seems to hold its edge better than plain steel tubing. I have used this technique before for punching holes in gaskets, or other thin soft material. Just back up what you are punching with a scrap piece of chipboard, or soft wood and hit the punch with a hammer. It obviously would not work in a production setting, but for short run jobs like this it works fine. For the rectangular holes for the retainers, just squish a round tube in a vice.
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In order to help reinforce the holes and perimeter edges, a light coat of epoxy was brushed on. It was also applied to any of the bends to help strengthen them.
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To be continued...….
