Do Fiberglass C3 Corvettes Have Rust Problems?

Greg Zyla
Hello Greg, and thanks for your interesting articles. I am a Corvette lover and am planning to buy a C3 Corvette in the future.
Since Corvettes are fiberglass bodies, my friends tell me that even though I won’t find rust up top, make sure I check the underneath for rust. Can you give any tips? Are they good buys? Thanks very much. George S., Mountain Top, PA.
George, your friends are correct. Even though a collector car might look 100-percent beautiful on the outside, and not just Corvettes mind you, underneath is where you’ll find major problems due to rust. So, let’s check out what to look at on these C3 Corvettes, built from 1968 to 1982.
As you note, these Corvettes come with “non-rust” fiberglass bodies, but they are built on a steel chassis just like any Nova, Camaro and Impala from those same years. Wheel wells are prone to rust on any car or truck, so check there first.
Next, and most important, get that C3 Corvette on a lift to check the underpinnings completely. The earlier C3 Corvette’s boxed in frame came with holes stamped into the chassis to allow for easy installation of those beautiful side pipes that were optional. Instead of making a punch hole, the Corvettes were sold with holes intact, which as the years went by didn’t fare well with rain and damp debris. The result was main chassis rails that rusted pretty badly, and it’s an area that must be checked for structural integrity. Many a nice C3 from the outside is a rust bucket underneath, so look for welding patch jobs and, worse yet, there are areas that may be rusted so badly you won’t be able to see them with the naked eye. When you see the frame rail holes, put a mini-scope in there or use a finger to feel for rust particles, which are a sure sign of further rusting.
Next, the frame rails can rust from the top down, ala rain water flowing from the top to inside the door area and down via the front A-pillar. These rust areas are covered by the carpet and will rust the frame from the top.
Corvettes 1975 and prior had fiberglass floors, so you didn’t have to worry about rusted floors. However the C3s from 1976 to 1982 had the steel pan floors just like all the Chevy siblings. Every car collector knows that steel floor stampings are another area of high rust contamination as explained when rain utilizes the A-pillar for a “free flow” runway in what’s called the “birdcage” to the floor pans resulting in both front and rear rust damage. Since they are all prone to this rust, make sure the C3 you seek has decent floor pans and rust free birdcage areas. Granted, the floor pans can be repaired, but If there’s rust on the frame rails in addition to the floor pans and door jams, quickly walk away from this car. Remember, some rust problems on certain cars are not that expensive to fix, but when it appears on a Corvette frame rails and birdcage it is VERY expensive to fix, if it can be done at all.
Check the body for cracks instead of dents. Corvette C3s are prone to body cracks and interior creeks and rattles mainly because that’s how they were built. As or the cracks, it’s better to just live with it as it won’t hurt anything and most all C3s have them somewhere. I had a friend who had a C3 with a removable hardtop and when that top was on, which was most of the time, it sure made lots of noise. Ditto goes for the T- tops, too.
Also, you’ll probably experience some headlight vacuum opening issues (check for leaks) along the way and maybe some easy to fix carburetor issues.
On the plus side is that all C3 Corvettes come with either a small block 350 V8 or a big block 427-454, which are all easy to work on. You will actually be able to change spark plugs on a Saturday morning instead of being relegated to a quick wash and wax on the modern day Corvettes. Replacement parts are plentiful, too, another plus.
Finally, the market values of C3 Corvettes are all over the board. If you choose a 1969 427 tri-power with 435-horses, you better have a really big wallet. Then again when you get into the later 1975 and up “smog” engine Corvettes, you can snag a real nice one for $7,500 or less. The reason there are more C3s out there is due to the generation’s long run from 1968 to 1983. In between the two dates are a plethora of Corvettes to choose from in all states of dress.
If successful, please let us know what you buy, George, and send a photo, too. 
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