birdgage rust C3

[Carol Ferguson]

My husband and I have recently looked at a 72Lt1 . We were allowed to look at
the birdcage and the car had a considerable amount of corrosion in this area. Does this corrosion take place due to a leak in the windshield?
The car in question is supposedly a 56k original mile car.How could there be so much corrosion in a low milage car? When NCRS judges examine a car is
this area a consideration in judging? How expensive of a repair job is this?
Frame off repair?

As recent NCRS members we were thankful to be tipped off about examining
birdcage area by other members on this board. We are grateful and we thank
you from helping us prevent an expensive mistake.

[Joe L.]

Re: birdgage rust C3

Carol------

1) A leaking windshield is one possible cause of birdcage corrosion, but it's not the only possible factor. Cars which are driven in corrosive environments (like salted-road winters) are especially susceptible to metal corrosion of all kinds. It takes very little salt exposure to get corrosion started. If the frame is rust-free, then it's unlikely that salted-road corrosion is a factor here;

2) Corrosion, be it birdcage or frame, has very little to do with miles driven; it's a TIME thing. Once corrosion gets started, especially from corrosive environments, it proceeds inexorably regardless of how much the car is driven;

3)The birdcage corrosion will likely not be much of a judging issue since it's usually pretty much unseen. However, that doesn't mean that it's not a problem. It's a BIG problem for serviceability of the car and future resale considerations (unless you find a "fish");

4) birdcage corrosion may or may not require a frame off repair. If it's limited to the windshield area, a frame off will not be necessary. However, if it's more extensive, then a frame off will likely be necessary to perform all of the birdcage repair. Of course, if the frame is seriously corroded (and, often, frame corrosion occurs from the inside), then a frame off is necessary;

5) birdcage corrosion damage is VERY expensive to repair. Even if only the windshield area is involved, it's a big job. The more extensive the corrosion damage, which is often not discovered until one gets "into the job", the greater the expense. At some point, repair is not practical within the value of the car;

6) birdcage corrosion damage DRASTICALLY reduces the value of a car, especially considering the "unknowns" regarding the extent of the damage; if some damage is confirmed (as you have), one does not really know how much more there might be. In virtually all cases, the reduction in value of the car due to corrosion and RISK associated with buying a car that may have even greater corrosion, is FAR, FAR greater than any seller is willing to accept. Either they wish to underestimate the cost of repair (which is normal if one is a seller) or they figure they can find a neophyte buyer who won't find out about the corrosion until after owning the car for awhile (which is, also, normal if one is a seller).

[Carol Ferguson]

Re: birdgage rust C3

THANK YOU Joe My husband and I had NO idea that there was a birdcage problem
with Corvettes. We always just inspected the frame from underneath the car.
We have seen several cars doused with undercoating to probably cover up frame corrosion.

My husband wanted me to ask if there is a diagram somewhere showing
how the birdcage connects to the frame of the car?If there is severe
corrosion I imagine that the winshield post becomes mobile?

Scary stuff indeed! Thanks!

[Michael W.]

Re: birdgage rust C3

There's a quick way to see if birdcage rot on a shark is terminal or not. Remove the kickpanel outboard of the driver or passenger's footwell. You will see the lower part of the steel pillar post running down from the windshield frame, this part also acting as the mounting point for the door hinges. If you see rot there, put the panel back, thank the seller and run as fast as you can. You don't want that car.

[Joe L.]

Re: birdgage rust C3

Carol------

The best information regarding the configurations and attachments of the birdcage and frame can be found in the Corvette Assembly Instruction Manual. The best information can be found in the particular year AIM for the year model you're looking at. However, any C3 AIM will provide general information applicable to all C3s.

In cases of extreme windshield pillar rot, the windshield assembly does "move rearward". This can be especially noticeable with convertibles. What often occurs is that the owner notices that the convertible top keeps getting "loose". However, it's not the top getting loose; it's the windshield frame assembly getting "loose" and moving incrementally rearward. Not a good thing to find out.

[Chuck R.]

Re: birdgage rust C3

When I got into pulling my 68 apart, the rust was so extensive, it took out the sills that run under the rocker moldings and connect the front cage assembly to the rear.

That was enough for me, I bit the bullet and purchased a stripped body from Colorado that was absolutley beautiful for a very reasonable price. Shipping costs ..... now that's another story.

What surprised me though was that the pillar posts behind the kick panels were in great shape but the windshield pillars and the sills were shot. Go figure.

If your into keeping THAT body with THAT car, and your willing to spend the coin, then go for it! But from my perspective, it will more than likely be moving from one can of worms to the other.

I can fax you a copy from my A.I.M. if you would like.

Good luck and be careful.

Chuck

[Paul L.]

Re: birdgage rust C3

Carol,
Here is a diagram of the birdcage. Warning: It is a large file so as to show detail.