We can hear it already. "How to repair rusty Corvettes? Corvettes are fiberglass and fiberglass doesn't rust!" Right-and wrong. The exterior body panels on Corvettes are fiberglass, or maybe a better way to say it is glass fiber-reinforced plastic, and these plastic panels will not, can not rust. On the other hand, all of those swoopy fiberglass panels are attached to steel inner structures, which are in-turn bolted to a steel frame. And steel rusts.
Corvette frames with rust-through problems, particularly '63-67 and '68-82 (probably due to the design of the side rails and the rear axle kick-up) are, unfortunately, relatively commonplace, especially in the Rust Belt regions. Nearly as prevalent, but hidden away beneath body panels and moldings, is severe corrosion of the steel (internal) windshield pillar and cowl side/door hinge structure on C3s. These structural pieces are nothing but stamped sheetmetal parts that have been spot-welded together to form the cowl sides and windshield framing. They're box sections with open centers, seem to be prone to leakage, and don't drain well. In other words, the perfect recipe for rust.
The top and face of the dash...
The top and face of the dash is removed and the wiring harness is moved aside. This protects the parts as well as providing more room to work. This is also an opportunity to inspect the cowl top and sides for rust or water damage, and to make any needed repairs.
It must be a heartbreaker to have what you think is a nice, solid Stingray only to inadvertently discover, by having a windshield replaced or when removing molding for a fresh coat of paint, that your fiberglass-bodied car has structural body rot.
Nick Conti runs a high-end autobody and paint facility (Conti Custom Auto, 25500 Joy Blvd., Harrison Township, MI 48045, 586/954-1929) in the Detroit-area. Recently, a customer brought in a lean '71 Corvette coupe for a new exterior paint job. A good quality repaint requires removal of stuff like bumpers, grills, lights, emblems, and moldings-slapping masking tape over them is the shoddy and cheap way to do it. When they pulled the windshield moldings, it was immediately and readily apparent why the car had leaked around the windshield-portions of the inner, steel windshield frame were almost completely rusted away.
The procedure starts with...
The procedure starts with deciding exactly where and how the cuts are to be made. Nick Conti opted to split the passenger side-pillar at the original seam, removing the rusted upper pillar from the inside of the non-rusted lower frame with a spot weld cutter and an air chisel.
This doesn't necessarily mean the kiss of death for a nice old Vette. Since the corrosion had NOT spread into the cowl sides (the door hinge structure), extensive (and expensive) reconstruction or a complete restoration wouldn't be required. Nick was able to locate a solid and rust-free used C3 windshield frame from a local Corvette salvage yard, and that recycled part would allow him to affect a thorough, yet reasonably priced repair.
The keys to a successful repair of this sort are to take careful measurements of the original car, careful measurements of the replacement part(s), more careful measurements, neat and clean cuts, and top quality welding. The difference between a successful repair and total failure is accurate measurements. Close doesn't count; the windshield glass can't be forced back into a frame that's a fraction of an inch too short or angled steeper on one pillar than the other. Precise measuring and cuts, coupled with the labors of a skilled craftsman result in a top-quality repair job. Here's how it's done...
This is what the passenger-side pillar looked like after the moldings and windshield glass were removed. Essentially the entire right-side pillar, almost from the base of the windshield, must be replaced. The rot on the driver side is confined to the upper corner so the VIN "tag" (where the number is stamped into the pillar and visible through the windshield) can remain intact.
Here's our replacement windshield frame and cowl top assembly, clean and rust-free, with a portion of the T-top support still intact. This clip cost approximately $300 from the local recycled Corvette parts dealer.
The T-top brace, which runs fore and aft from the windshield frame to the rear roof "hoop," must also be accurately trimmed to fit. Nick chose to make his cuts exactly in the center of the mounting screw pattern for the T-tops' front guide plate, which would give him an excellent reference point for uniting the "new" section to the car's structure.
The final cut on the replacement cowl and windshield pillar assembly is on the driver side. The cut line is marked with masking tape (much easier to eyeball than a scribed line), and Nick makes the cut a little on the long side, which leaves some material to grind or trim to achieve a perfect fit. It's a LOT easier to trim off a little excess material than to try to fill up a gap in the two sections.
Nick squares the edges of the cuts on the original body structure with a grinder, then does a trial fitting. He'll check all dimensions (height, width, angles) of the clamped together replacement assembly against the measurements he took on the car before the first cut was made. A perfect fit is the goal, and by taking careful measurements, making exacting cuts and precision final grinding, a perfect fit is achieved.
In addition to the clamps, Nick bolts the T-top anchor bracket/guide plate to the center support, which helps align the replacement (forward) section with the original (rear) section. Then he starts welding the replacement section to the original structure. Tack welds are first, then, after unbolting the anchor bracket/guide plate and rechecking all dimensions yet again, the seam is welded up solid.
With the windshield trim clips and the dash and instrument panel components re-installed, Nick has the windshield professionally fitted, using the proper adhesive/sealer materials. This is not only to prevent leaks-both the windshield and its frame provide support to the entire body structure. This Shark is good to go for another three or four decades.