C3 aftermarket windshield fits poorly

[Leon Beha]

As part of a full restoration of my 76 Corvette Coup, I am replacing the top and top corners of the windshield frame. I also welded in new metal in a small surface on the left side post. The right side post cleaned up down to shiny steel. When I dry fit using the old cracked windshield, it fits against the upper windshield frame perfectly on the right side and across the center top and bottom frames. The left side has a 3/32 inch gap between glass and the bonding surface of the side post. That gap gets narrower until the windshield touches down about a foot in from the lower left corner and about 6 inches in from the top corner. When dry fitting, there is a slight twist in the windshield because it takes little effort to lift the top right corner 1/16 to 1/8 inch off the frame without lifting the whole windshield. My test windshield is not the original one and I will be installing a new windshield that may fit differently than it.

I plan on using POR15 top coat around the perimeter of the sealing surface and 3M one step primer 08681 under the glass. I will install the replacement windshield with 1/4 x 3/8 inch daming tape and 3m 08609 urethane.

I have several questions:

What is the expected variation in shape of an aftermarket windshield?
When dry fitting, how much of a gap is acceptable?
How much out of plane twist is acceptable?
Is my planned prep and installation procedure correct?

Thanks to all for your help.

 

[Tom Bryant]

There will be variances in windshields even from the same manufacturer but they will be within tolerance. The 3M One Step gives an excellent adhesion between the clean painted windshield frame and the glass. Glass does flex more than you would think. Never push or pry on the edge. A 3/8" bead of urethane will more than make up for slight variances in the frame. I don't do many but I did invest in a pair of those big suction cup things with the handles on them. Got them at Harbor Freight but they do the job. I like to set the new glass in place, not touching the frame anywhere on the edge. Differences in temperature will move the frame and an edge pinch could crack the windshield. When I get it centered I put a strip of masking tape across the top onto the frame and bottom onto the cowl and make a mark on it. Then cut the tape with a razor and use the marks for alignment when I reinstall it with the urethane in place. The glass must be cleaned with alcohol where it will contact the urethane.

Are you going to use a reproduction date coded glass?

Tom