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1955-1959 Chevy Truck Firewall Replacement - Firewall Fixin'Swappin' To Smooth Sheetmetal From the May, 2009 issue of Custom Classic Trucks By Kev Elliott
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While "removing firewalls" will have a totally different meaning to computer geeks, to us gearhead types it will always have connotations of making space for a bigger motor, because if the firewall is in the way, that's usually the reason why, not to mention a new, shaved firewall looks much better. Direct Sheetmetal manufactures a recessed firewall for '55-'59 Chevrolet and GMC trucks in addition to many others, which not only offers improved engine clearance but also cleans up the firewall without having to weld plugs into the numerous holes in the stocker. When KA Custom in Huntington Beach, California, told us they were about to install such a piece, we headed straight over, though it soon became apparent that there'd be a little more work involved than first thought, as the cab the customer supplied was a little worse for wear, and had been involved in a substantial collision at some point in its life. Now mounted on a straight frame, the firewall and right side of the cab was bent, twisted, and generally a mess. However, the mounting holes in the floorpan were still in alignment (it fit the chassis perfectly) so even though some of the floor was kinked, it wouldn't take much to return it to its rightful shape, especially given we'd be cutting much of the damaged sheetmetal out. Kevin Francis at KA Custom had originally intended to reuse the lower firewall section, but after inspecting the cab when it arrived, and realizing what would have to be done to repair it, he opted to fabricate his own lower piece, which we'll show you in the second installment of this story. Meanwhile, let's get on with it, and straighten out that cab.  Here's our firewall recipient,...  Here's our firewall recipient, a rust-free '55-'59 Chevy Big-Window cab that had received some crash damage sometime in the past, then was swapped onto this frame.  The cab didn't look bad at...  The cab didn't look bad at first, but subsequent inspection revealed it had been hit hard, pushing the motor into the firewall and putting a crease in the front of the cowl, above where we'll be replacing metal. The A post closing panel behind the front fender had also taken a hefty smack and would require replacement. Pushing the firewall back bent the floor, but the good news was that the door apertures measured the same so the A post wasn't pushed back.  Using a torch to soften it,...  Using a torch to soften it, all undercoating that covered spot welds or would be in the way of plasma cutting was scraped off.  The top section of the firewall...  The top section of the firewall was removed with a plasma cutter, around the upper and side flanges and across just below where the vertical part of the firewall bends and becomes the floorboard. A grinder and cutting disc would work just as well but take longer.  Wearing gloves--irrespective...  Wearing gloves--irrespective of the heat generated by the plasma cutter, the edges of steel sheet are sharp--Kevin removed the old section of firewall. You can see from the section that remains on the cab just how far back the firewall had been pushed in the center.  The old and the new. No comparison...  The old and the new. No comparison really, is there?  After removing the transmission...  After removing the transmission cover, Kevin could assess the floor damage. The area in front of his foot was forced down when the firewall came back, but the mounting bolt at the front of the step was still in its correct location, making this an easy repair. If that had moved too, the cab would require pulling back to shape on a jig or be scrapped.  Using a 2x4 and a floor jack,...  Using a 2x4 and a floor jack, the floor was pushed back up along the crease, while another 2x4 was hammered down either side of the crease. When the pressure from the jack was released, the floor remained flat. The lower section of firewall had been pushed forward again too, back to its original position. The trick is to work out how it's been damaged and then work backwards from that point.  With the damaged A post closing...  With the damaged A post closing panel roughly cut off, the kink in the cowl (arrowed) could be worked out. With much of the stressed and bent sheetmetal now removed, this came out easily using a pry bar and a block of wood to press against, spreading the load on the inner panel.  Kevin could now turn his attention...  Kevin could now turn his attention to the upper firewall area, again using a length of 2x4 and a hammer, this time through the glovebox aperture, to beat the metal back to close to its original shape.  With most of the damage roughed...  With most of the damage roughed out, Kevin drilled out the spot welds holding the remaining section of firewall in place. He prefers to use a Roto-broach, but you can buy dedicated spot-weld removal drills.  This is what you should aim...  This is what you should aim for, each spot weld drilled out but without drilling all the way through the second layer of metal behind that which you wish to remove.  With all the welds drilled...  With all the welds drilled out, the section of firewall was removed and discarded.  Once the remainder of the...  Once the remainder of the firewall was removed, Kevin was able to dress the lip and straighten it in preparation for the new sheetmetal. The remainder of the kink in the upper firewall was also straightened using the hammer and dolly at this point, having been roughed out in step 10.  Ready to install the new section....  Ready to install the new section. Note the original firewall was split down the center of the trans tunnel to allow the passenger side of the firewall to come forward more easily while the floor was being repaired. You can see it's back to where it should be now.  As the new firewall is recessed,...  As the new firewall is recessed, the section of the steering column support bracket nearest the center of the truck will no longer fit, so Kevin trimmed it and will rebuild it to reach the new firewall later.  After deliberation, Kevin...  After deliberation, Kevin decided he'll fabricate the toeboard sections of the firewall rather than attempt to repair the damaged original, and we'll show you this in part two of this story, along with replacing the A post closing panel.  Clamped in and ready to weld....  Clamped in and ready to weld. As this particular truck had been damaged, Kevin took care to ensure everything was in alignment, and that the fold halfway down the firewall was in the same place on both sides.  Here's the part of the steering...  Here's the part of the steering column support that didn't require trimming, nice and snug against the inside of the firewall. Fits pretty good huh?  As the upper firewall has...  As the upper firewall has a return on the lip it makes clamping the new and old pieces together a little tricky. Using a Double D steering shaft solved that problem, though of course a length of x -inch box section would work just as well.  When the new section is clamped...  When the new section is clamped in place the aim is to have as minimal air gap between the new and old as possible, for a strong rosette weld. The lip will be cleaned prior to any welding.  You can't have too many clamps!...  You can't have too many clamps! Kevin welded the holes in an irregular order to minimize warpage, jumping between holes in different areas rather than working from one end to the other.  This is what you should be...  This is what you should be aiming for, nice strong rosette welds with good penetration. You can spot this as bad welds won't show any color distortion on the back side of the second panel, whereas welds with good penetration will `burn' right through the new metal.  Until next time, the hard...  Until next time, the hard work is done, just needing a couple of neat fabricated lower sections to finish things off.
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1959 Ford F-100
Scott Oshinki rebuilt a 1959 Ford F-100 for his father-in-law Art Carney....
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