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

You can see how much we trimmed from the original toe panel piece. The metal cut away is already part of the Goodmark main floor, so it was redundant to our needs. Goodmark's panels come with extra metal stamped in to allow for any fitment issues, and the usual production variances of cars.
You can see how much we trimmed from the original toe panel piece. The metal cut away is a
An area where custom fabrication was needed was the seam area where the cowl/rocker/cowl ears meet. On both sides this area was rusted badly from being a moisture collection point with no draining ability. These areas had to be repaired before welding in the new toe panels. Unfortunately, Goodmark doesn't make replacement sheetmetal to fix this particular problem, so the CARS crew started measuring, then cutting out the oxidized areas so fresh metal could be welded in.
An area where custom fabrication was needed was the seam area where the cowl/rocker/cowl e
With the offending pieces gone, the first step was to weld in a new rocker panel extension, since this piece is the foundation for the other repair work around the cowl and firewall.
With the offending pieces gone, the first step was to weld in a new rocker panel extension

Before welding in any new metal, the whole area was hit with an abrasive disc to provide rust-free welding surfaces. This was also done to make sure there wasn't more steel that needed replacing so the toe panels could be installed.
Before welding in any new metal, the whole area was hit with an abrasive disc to provide r
With the rocker extension tacked in place, the trimmed toe panel is fit-checked, and used as a template to mark what rusted metal needs to be removed.
With the rocker extension tacked in place, the trimmed toe panel is fit-checked, and used
Once again, the cutting wheel goes to work ridding our project car of more corroded steel. Again, measure several times before cutting anything out.
Once again, the cutting wheel goes to work ridding our project car of more corroded steel.

On the right you can see the rocker extension, and how it relates to installing the toe panel piece. The fit on the Goodmark piece was almost perfect, but a little massaging was necessary to get the fit just right.
On the right you can see the rocker extension, and how it relates to installing the toe pa
Here's a close up of the finished rocker extension. Because of rodent debris, any water that accumulated in this area of the body couldn't drain out, meaning it became a breeding ground for rust. This part of the body affects the mounting of the toe panels, floor pans, outer/inner rockers, and the cowl ears, so it had to be repaired so the individual parts would have a solid mounting point. Once everything is welded in place, it'll be painted with some zinc oxide primer to protect against corrosion while the rest of the car is being worked on.
Here's a close up of the finished rocker extension. Because of rodent debris, any water th
After the toe panel was welded in, all the welds were ground down and smoothed. Once the sheetmetal work is done and the car is fully primered/painted, you won't be able to tell where new steel was added.
After the toe panel was welded in, all the welds were ground down and smoothed. Once the s

With the toe panel in, we found it wasn't quite wide enough on the rocker side, and needed to be modified a bit.
With the toe panel in, we found it wasn't quite wide enough on the rocker side, and needed
The rocker end of the toe panel was cut off and moved into position so a simple piece of steel could be welded in to give us the correct width. Because of how the main floor piece slides into position in the car's structure, we did not fully weld the toe panel in place.
The rocker end of the toe panel was cut off and moved into position so a simple piece of s
With the body mount plate full repaired, it was coated in zinc oxide primer to protect against corrosion before the reinforcement cup is welded back in. The reason for using the zinc oxide is while it protects the metal from new corrosion, it still provides a fully weldable surface for later work.
With the body mount plate full repaired, it was coated in zinc oxide primer to protect aga

Before reattaching the body mount, the area behind it was coated with zinc oxide primer. The primer neutralizes any surface rust while also preventing new rust from forming and screwing up all the repair work that's just been done.
Before reattaching the body mount, the area behind it was coated with zinc oxide primer. T
Here's one of our repaired body mounts primered and ready for reattachment to the body. The A-body ragtops used a special mount that featured an extra body bushing/cushion for support since there wasn't a roof structure to bolster rigidity. The inner cushion doesn't have a bolt going through it like the neighboring mount; it just helped support the body's weight and was held in by pressure. If all goes well, in our next installment we'll be test fitting the Chevelle to its new Art Morrison chassis, finalizing position of the main floor pan assembly, and be welding everything together so we can start work on the trunk area.
Here's one of our repaired body mounts primered and ready for reattachment to the body. Th

SOURCES
Goodmark Industries 625 Old Norcross Road Suite E Lawrenceville GA 30045 877-477-3577 www.goodmarkindustries.com	Classic Automotive Restoration Specialists Inc. 8235 Nautical Point Drive Belews Creek NC 27009 336-595-3900 www.classicautomotiverestoration .com