Firewall Smoothing Guide - Smoothin' & Fillin'

When building a custom vehicle, it's the little things that matter. Often enough, these items are easy to overlook or even ignore. However, when all the little details are tallied up, they can dictate whether you have a show-winner or an also-ran. Take, for example, this 1971 Monte Carlo firewall. It's a basic GM A-body, and all the firewalls look the same. The plans for this firewall include subtle smoothing. We didn't go all out and make it as flat as a tabletop; that would be too boring to look at.

Armed with a welder, grinder, body hammers, and body filler, a clean-looking firewall that retains the OE look can be easy enough to do. This Monte Carlo was last seen on our pages about a year ago, and now it's nearly ready for paint. We followed along as Harrison Ortis of Harrison Restorations (Upland, California) ironed it out. It only took a few days to do, but the results speak for themselves.

The humble GM A-body firewall....        read full caption The humble GM A-body firewall. Even when the hood is opened, it's only partially visible. Still, a smoothed firewall can add greatly to a vehicle's underhood appearance and can mean the difference between finishing First and Second in a car show. From the production line, the firewalls are utilitarian in purpose, filled with bumps, dips, wrinkles, and body caulking.	The area that will receive...        read full caption The area that will receive most of our attention is where the firewall and cowl vent pieces are joined together. Spot welds and body caulking are what keep it together, but they don't look all that great. The first order of business is to work over this bare metal edge.	The generous amounts of body...        read full caption The generous amounts of body caulking applied at the factory are removed with a hammer and chisel.
The residue of the caulking...        read full caption The residue of the caulking is ground out with an air grinder. The goal here is to clean it all the way down to the bare metal.	A final photo here shows how...        read full caption A final photo here shows how clean the joint is before we start working it over.	The goal is to roll the lip...        read full caption The goal is to roll the lip over. First, a body hammer is used to fold the lip up along the entire leading edge.
Once the edge is folded up,...        read full caption Once the edge is folded up, a hammer and dolly are used to fold it down over itself and pound it into place.	Here is the final result of...        read full caption Here is the final result of the rolled lip. The sharp edge from the factory is now gone, but we are not done yet.	The entire seam is now tacked...        read full caption The entire seam is now tacked into place with the welder.
Even though the metal is thicker...        read full caption Even though the metal is thicker here, we are still careful not to apply too much heat and warp it. Everything is tack-filled until a solid, seamless line is achieved.	Afterward, all the welds are...        read full caption Afterward, all the welds are ground down and smoothed as much as possible.	The dimples on the firewall...        read full caption The dimples on the firewall and spot welds that were not accessible with a hammer and dolly were all tack-filled with the welder.