1960's - 70's GM A-Body Stationary OEM Installation Details

So you have reached the point of needing to install your windshield or rear window of your late 60’s – early 70’s GM A-body and you’d like to know just how the factory did it. Well today there are options which are frequently debated for the proper installation of stationary glass and this post isn’t attempting to advocate Urethane vs. Butyl, but instead show how the factory did things back in the day.

The fact is that GM used a dam tape and sealant produced by the Thiokol Corporation to set their stationary glass. The main purpose of the dam tape was to contain the excess squeeze-out of the sealant so that it flowed into the channel as opposed to into the passenger compartment. In doing this, they were able to have a visually pleasing aesthetic so that the squeeze out wasn’t visible when looking from outside into the window (front or rear). There was a bit of a secondary benefit of the dam which to a degree held the glass at a proper height so that the stainless trim fit well to the window. It is important to note that the dam tape used was of a reasonably low durometer and was easily deformed and so the finished height of the glass wasn’t always “fixed” by the dam tape height (as you can see in the comparison of pieces removed from the front and rear window from an original OEM-installed glass set).

While the “L” or “J” profile dam tape is no longer available today, there are dam tapes available that in fact are better for the restorer should he/she decide to re-install using a Urethane system. Today’s tapes are of a higher durometer and provide a stiffness which can accurately hold the glass at the proper height for a more sure installation. Of course if the installation is going to be done with Butyl tape, then the installer need only have the proper diameter tape to set the glass to the proper height so that the stainless trim will fit tight to the glass.

It should be noted that in modern cars the stationary glass is set in a Urethane bed and no dam tape is used. The black edge or “Frit” around modern windshield has three purposes. The first is to provide a good surface for adhesion of the sealant, the second is to obscure the sealant bed so that the squeeze out cannot be seen and the final is to provide a UV barrier to protect the sealant from degrading in the sun since few cars use stainless trim today.

We have also included a diagram so that if you have changed your glass thickness from the OEM (today’s replacement glass is thinner than the OEM glass), or had to install new trim clip studs then you can calculate the dam tape height so that your glass goes in just right (or calculate the installation height needed for your studs).

A copy of these slides is available in PDF form as a free just email us at info@beldenspeed.com and request it we will gladly send one to you!