One of the items it seems important to check before buying a used C3 is the bird cage for rust. How does the bird cage get rusted out in the first place? Is there that much water leaking in due to the design? Is it worse in climates where the road is salted?

I can see how the undercarriage would rust from road salt, but the bird cage too?

 

Hi belair,
Because of the design of the windshield frame and the steel structure for the firewall and hinge pillars rain water had numerous opportunities to get very close to that steel.
With-in a few years the system used to seal the windshield, the sealants used on the cowl and a-pillars, and the zinc chromate paint used on the steel ALL began to fail.
At that point the water started to have access to the steel, and the rust began. Even if a car was stored inside the humidity in the air in some parts of the country was enough to keep the rust process going. Cars that spent extended years outside had catastrophic rust.
The same problem was occurring on the frame. It's worse right in front of the rear wheels where a combination of road debris, salt from icy roads, and water literally destroyed some frames to the degree that the body was holding the car together.
The only thing uglier than a severely rusted Corvette is the look on an owners face when he realizes what it's going to take in time and $$$$ to repair his car IF it can even be repaired.
Nasty Stuff!
Regards,
Alan

 

Some photos of a rusted birdcage. Owner went to extreme lengths to repair. Nice job...

http://forums.corvetteforum.com/c3-g...-pictures.html

 

Yeah... that was a beautiful piece of work he did. My Bird Cage is going into the shop this Fall. I'm already lubricating my wallet hinges because I'm positive it's going to get a workout.

 

I get the impression that once this starts it is progressive. If I'm reading your reply correctly, Alan, the seals break down in a couple of years due to the design. Is it common to find on the majority of C3s?

 

Hi belaire,
The failure of the seals, sealing material, and paint was I think a function of age (shrinkage/ drying out), and just enough body flexing to crack the seals loose.
There were areas in the structure that by unintended design encouraged water to gather as the sealing deteriated and cause the rust to become catistrophic.
This is true for the upper windshield corners, the lower windshield post/ cowl connections, the #2 body mounts at the bottom of the hinge pillar, the rocker channels, and the #4 body mounts.
The road salt used in that era had the greatest effect on the rocker channels, #4 body mount, and the area of the frame at the pickup/trailing arm pocket.
There are some VERY rusty cars, more with SOME rust, and some with NO rust. It often has to do with where the car lived and how it was stored. Probably the worst situation is a car stored in a building (barn/garage) with a dirt floor. The car got damp and STAYED damp (even more so than a car stored outside) and the rust worked 24 hours a day.
There are certainly cars without rust to be bought, but they take some perserverence to find. There's really no reason to buy a rusty car... they generally break your heart, spirit, and wallet!
Regards,
Alan

 

I hope Alan would concur... The rust is progressive UNLESS you use POR-15 (or maybe chassis saver) which converts the iron oxide to iron phosphate, which stops the progression. A search on that product should reveal various degrees of successful results... But if it's frame or birdcage SURFACE rust, you could be ok with a coating of a similar rust converter. Unless the car has been recently restored or was kept in a climate controlled environment you will have some rust.

However, if you have significant rust (holes) you're likely better off avoiding the car altogether. Repairs or replacement are prohibitively expensive in many cases.