ensuring correct C3 nose height during restoration

[Mark A Hart]

Background:
During the frame-off restoration of my 1969 coup, I attached the body to a temporary dolly but I am unsure that the nose is aligned in the up/down dimension. The flex in the unrestrained front end allows the nose to move up and down a few inches. I want to avoid alignment problems when I repair some fiberglass damage to the front fender lip (the area closest to the tire).

I have an adjustable brace from the radiator support bolts to the dolly. The brace from the bottom of the radiator support to the header bar is installed. I suspect that the nose is too low. Probably, the ambiguous flexing in the front end occurs near a plane that could be drawn about where the front wheel spindles would be.

What I have tried so far:
In the hood surround, I placed a 4-foot straight edge in the trough (lip) that captures the hood and attaches to the inner fenders. At the moment, there is one-inch deviation from a straight line from near the hood latch to near the hood hinge on the right side. The deviation is a bit greater on the left side.

Questions:
Is there a reliable reference measurement to confirm that the nose is at the correct height? Is there a reliable reference to body mounts 1, 2, or 3? Is there another indicator of the proper nose height beside the hood lines?

[Chuck S.]

Re: ensuring correct C3 nose height during restora

Mark, in the 69 Corvette Chassis Service Manual there is a diagram of frame dimensions on page 2-6.

Use the datum height to the No. 1 body mount (15 1/2") and the datum height to the lower flange of the frame rail at the very front end (14 3/8"). You can figure out from that where the frame horn extension bracket mounts relative the No. 1 mount. The front cross member bolts to the extension brackets, and the front cross member supports the radiator support.

I assume you have your frame and the extension brackets available to measure the details. The tricky part will be picking a reference point on the cross member since it is at an angle...I would temporarily mount the cross member and project the position of radiator support mounting holes over to the extension bracket. Make the measurement, do the math. Body shim thickness should not be enough to be a factor.

I suspect the deflection of your front end begins further back than you think...probably where the front fenders are bonded to the bird cage. I doubt that the sag would have a big effect on repairs to the wheel opening, but leaving the front end unsupported for an extended period is not a good idea.

[Terry F.]

Re: ensuring correct C3 nose height during restora

What Chuck says is true. Hopefully the body is on a jig that is a mock up of the frame mount positions and is reasonably true to those points. The mock-up should also include the radiator suport locations. If the radiator core support is installed and the front nose brace is attached then you have the correct nose height.

When the nose sags there is a lot of force generated at the bonds at the top of the firewall were the hood surrounds attach. You will either break the bonds or pull the little corner panels off (located at the top of each corner of the firewall under the hood surround). They are a pain to fix.

To avoid this you should support the front corners of the fenders where the outside corner bumper braces attach. You will find that you can raise and lower this area a little bit and it will cause the fenders to flare out/in. I would raise it to what you think is a neutral position.

I found this out by replacing fenders. The sag is hard to see untill you try to put a fender back on the car. I would raise the corner untill I got the fender to align without twisting it. The process made me apreciate the forces involved. I realize you are probably not replacing a fender but just be careful not to make matters worse for yourself. Just some thoughts, Terry