A quick look at the stock...
A quick look at the stock firewall shows why someone would want to clean it up a little bit. That’s a lot of holes!
After last month’s inspection of his newest project and following its return from the sandblaster, our tech center main man Jason Scudellari tore into the sheetmetal repairs on our project ’56 Chevy with vigor. Replacing the cab corners, rockers, and part of the driver’s side door pillar, it soon became painfully obvious that one, if not both, of the cab’s doors were smoked. As Jason began searching for replacement items, it became even more painfully obvious that finding decent stock replacements wasn’t going to be easy, as it seems that this is a weak area of sorts for these trucks.
Not wanting to have the project sit idle while a good set of doors was sorted out, we decided to sit down and to see if we could come up with a few things that could be accomplished on the truck in its current state. We decided that it was as good a time as any to tackle shaving the firewall, as it wouldn’t affect much of anything down the road and save us a few hours of labor later on. And with a firewall that resembles Swiss Cheese and no plans for a total restoration, it made sense to smooth it out and fill all the holes in one, simple swoop.
Starting with a sheet of 18-gauge sheetmetal, Jason setup his workstation before cleaning up the firewall on the truck. From there, he made a pair of templates, one for each side of the hump, before transferring the shape onto the sheetmetal. Using his trusty Lincoln Tomahawk plasma cutter, the two panels were quickly cut out and then tacked directly over the stock firewall. While the original firewall could have been cut out and replaced with the new panels, there are numerous reasons Jason decided not to do it this way. First, leaving the stock firewall as-is ensures it retains its structural integrity. Cutting any portion of it out could let the front of the cab sag, twist, or move. Second, it’s quick and to the point. The goal was to smooth the surface of the firewall and this was the easiest way to achieve that goal. Third, it creates another barrier to bar heat, noise, and aromas from entering the cab from the engine compartment.
Setting an afternoon aside, we followed along as Jason took a flimsy, holey firewall and turned it into one smoothed out, tough panel. Little side projects like this are a great way to fill wasted downtime and can really speed up a build. Though it may seem a bit out of order, side tracking to something like this while waiting to finish another aspect of the build is what gets that build checklist completed. CCT
Since the plates are going...
Since the plates are going to sit against the stock firewall, the entire surface needs to be nice and flat. Holes with flanges, such as this one, need to be trimmed back.
A cutoff disc on a grinder...
A cutoff disc on a grinder make quick work of the flange …
… leaving the surface smooth...
… leaving the surface smooth and flat.
To ensure a clean and well-penetrating...
To ensure a clean and well-penetrating weld, the surface of the firewall needs to be in bare metal. A grinder with an 80-grit flap disc removes the primer easily and leaves a smooth finish.
Now the firewall is ready...
Now the firewall is ready to accept the new panels. Note that the entire area of the upper panel has been sanded down to bare metal. The first step is to make a pair of templates. A quick set of measurements are taken before being transferred to a sheet of paper.
Then, the sheet is taped to...
Then, the sheet is taped to the cowl of the truck and the shape of the panel is traced onto the template.
Once both sides are traced...
Once both sides are traced and trimmed, you can see how the panels will fit over the existing firewall sections.
The next step is to transfer...
The next step is to transfer the shape of the templates onto the 18-gauge sheetmetal.
The steel panels are then...
The steel panels are then cut out using a Lincoln Tomahawk 375 plasma cutter. Note that Jason is using a straight edge as a guide, clamped to the work piece to ensure a nice, straight cut.
Other cuts however can only...
Other cuts however can only be made by freehand.
Once the shape of the template...
Once the shape of the template is cut out, a grinder with a sanding disc attached is used to deburr the edges and to smooth out the radii of the curved areas.
Jason included a few other...
Jason included a few other items on his templates that should be pointed out. First are the hood hinge mounting holes. The hood hinges attach to the firewall using nutserts attached from the factory. Not wanting to remove the stock mounting point, Jason simple-drilled two holes on both upper corners that will allow the stock attachment point to be retained. He also placed two strategically located holes in the center of each template so that he can plug-weld the panel to the firewall. Doing so alleviates the chance that the panels will vibrate against the firewall as it essentially mates the two together in the center as well as the perimeter.
Before welding the panels...
Before welding the panels to the firewall, Jason flips them over and applies a coat of primer to prevent the inside from rusting. Note the aforementioned center plug weld holes.
Now the panels are ready to...
Now the panels are ready to be welded into place.
After ensuring that everything...
After ensuring that everything is aligned, Jason begins a series of tack welds using a Lincoln Power MIG 140c welder around the entire perimeter of each panel. Once the panel is completely tacked into position and given a final inspection, it is finish welded using a series of one-inch welds spaced liberally apart to avoid any warpage problems due to overheating.
To smooth things out, the...
To smooth things out, the grinder and flap disc package is once again used to knock the welds down and create a seamless appearance.
When it’s all said and done,...
When it’s all said and done, it’s as if the truck left the GM factory this way. A little body filler and some paint and you’d never know the firewall was modified. Note the center sanded areas of each panel; that’s where the plug welds were located.