1970 Chevy Chevelle Malibu Project - Firewall Body Mounts

Before we could start cutting out the rusted toe panel areas, the firewall body mounts had to be removed so we could examine them for rust damage and perform the necessary metal replacement. Here, Tommy Barber is using a clean disc to expose the factory spot welds so they can be drilled out and the support separated from the body.

Before we could start cutting out the rusted toe panel areas, the firewall body mounts had

Even though our A-body isn't a notable LS6, 396, or even an SS, it is still rare and valuable. Why? Do a search online covering Chevelle convertibles for sale and see how many pop up, and what they're going for.

Total Chevelle/Malibu production for the 1970 model year was 633,944 units. Out of that, only 7,522 convertibles were produced. That's right, every Chevelle convertible is a rarity. That's just over one percent of total production. Breaking that down further, only 381 were built with six-cylinder engines, while the rest were equipped with various V-8s. And when you figure in the usual attrition rate for older cars, substantially less are even still around, in any condition.

In part one, we began the general cleanup process, and survey to find out exactly what needed to be done. Extensive rust had eaten away most of the floor, from the toe panels all the way back to the trunk, and we left off with sliding the new complete Goodmark floorpan unit into place. After some further investigating as to how these cars were built at the factory, we figured out the toe panels had to be repaired before sliding the floor into place and getting it ready for welding.

Goodmark makes most of the metal we used in this part of the project, but there was some custom fabrication that had to be done when it came to the forward body mount plates, which we'll point out later on.

Follow along as we tackle part two of trying to get our convertible back into fighting trim, and handle some difficult metal repair.

Because this support is a key part of the car's structure, the factory used plenty of spot welds to secure it in place. The mount and firewall weren't in the greatest shape, so care had to be taken to make sure all the spot welds were drilled out. Just cutting through them with the air chisel wasn't an option, as that would irrevocably damage the convertible-specific body mounts, unavailable new from the aftermarket, and NOS/salvage replacements are hard to come by.
Because this support is a key part of the car's structure, the factory used plenty of spot
After all the welds were drilled out, Tommy used a pry bar to try and gently separate the mount from the firewall to reduce the damage risk from the air chisel. These mounts were spot welded in place at the factory before the body was painted, so there is no protection from corrosion between the two pieces.
After all the welds were drilled out, Tommy used a pry bar to try and gently separate the
After some gentle coaxing with the air chisel, the mount came free, and caused us to almost vomit. Typical of the rest of the area, the corrosion was pretty significant to the mount. The cup/reinforcement piece on the mount is also spot welded in, and that meant more drilling and separating so we could fully examine it and make any necessary repairs.
After some gentle coaxing with the air chisel, the mount came free, and caused us to almos

Here's the exposed area that was behind the mount. You can see where the air chisel went through the weaker/rusted out areas. The good news is a lot of this metal is being replaced with our new Goodmark toe panel pieces, but we'll still have to do some custom metal work to fully repair it.
Here's the exposed area that was behind the mount. You can see where the air chisel went t
Here's the passenger side mount removed. Same corrosion damage as the driver's side that has to be repaired before new sheetmetal can be welded in. Because the body was painted after these parts were welded on at the factory, the only protection from corrosion was from any primer/paint spray that managed to "sneak" into the area behind the mount. So, for 40 years, this has been bare steel exposed to the elements.
Here's the passenger side mount removed. Same corrosion damage as the driver's side that h
After sandblasting the mount, a special drill is used to break the factory welds holding the reinforcement plate to the mount. Because this mount is irreplaceable and unique to convertibles, great care was taken through this process so it wasn't permanently damaged.
After sandblasting the mount, a special drill is used to break the factory welds holding t

Not good. The rust had eaten through the reinforcement plate and mount and weakened both pieces severely. This may look hopeless, but the piece can be saved with a little fabrication and patient welding.
Not good. The rust had eaten through the reinforcement plate and mount and weakened both p
Here, the area to be cut out and patched is clearly marked for cutting. The lines on the perimeter of the mark are guides for locating the body cushion and mount holes so they can be properly drilled into the new latch piece.
Here, the area to be cut out and patched is clearly marked for cutting. The lines on the p
Jim Barber uses a cut-off disc to remove the cancerous area from the mount. This is where having the help of a skilled fabricator and/or restoration shop can be handy for the guy at home who is facing a similar problem.
Jim Barber uses a cut-off disc to remove the cancerous area from the mount. This is where

The passenger side mount was just as bad. Because the convertible's structure was so weakened with the floor rusting out, the body mounts were subjected to even more stress and pressure to keep the car from crushing itself like an empty beer can. Once the rust was blasted away, we found stress cracks around the body cushion and mount holes on both the passenger and driver's side pieces. Whenever you're dealing with a really rusty car with compromised structural integrity, take great care and thought before unbolting anything. A seemingly useless and unimportant bolt or weld could be the only thing keeping your project together!
The passenger side mount was just as bad. Because the convertible's structure was so weake
Once the patch piece is marked on a similar gauge of sheet steel, it's cut out using a pair of heavy shears.
Once the patch piece is marked on a similar gauge of sheet steel, it's cut out using a pai
Since the patch piece was flat steel, it was tacked in on one end, then progressively TIG welded and bent to match the shape of the mount. Before finish welding, the measurements for the body mount and cushion holes were rechecked to make sure everything was right.
Since the patch piece was flat steel, it was tacked in on one end, then progressively TIG

Here's the patch on the reinforcement plate. Once the welds cooled, they were cleaned up and the piece coated with protective zinc primer before being re-mated to the body mount.
Here's the patch on the reinforcement plate. Once the welds cooled, they were cleaned up a
While the repair work on the body mounts was taking place, Tommy Barber was working on the toe panel patch. Since our complete Goodmark floor shared metal with the toe panel pieces, both had to be measured and matched so any unnecessary metal could be trimmed away.
While the repair work on the body mounts was taking place, Tommy Barber was working on the
The patch is set in to check fit, placement, and see if any other trimming is needed. Just like with any sort of fabrication job, you can never measure too many times before cutting.
The patch is set in to check fit, placement, and see if any other trimming is needed. Just