by Bob Beranek
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As the title suggests, I have written about exposed edge glass several times before. However, I would like to address another issue about this particular style of glass mounting, especially pertaining to the windshield mounting. To get an understanding of some of the other issues surrounding this glass mounting style, please read my earlier posts.

Have any of you noticed that Original Equipment (OE) glass set in the opening is below flush to the roof top? Do you know why? Replacement technicians should pay attention for two important reasons.

  1. The glass is recessed in the opening for roof support. Why is the top pinchweld usually an “L” shaped pinchweld? The reason is that the vertical wall of the pinchweld acts as a stop for the windshield to assist in roof support. If an accident occurs, and the roof is depressed, the glass edge, the shear strength of the urethane and the vertical wall of the pinchweld, work together to help the roof and its structure from collapsing on the occupants. If the glass is mounted higher than the vertical wall of the pinchweld, then the glass can skim the roof and miss the wall support. This puts a great deal of dependence on the urethane adhesive and its proper use.
  2. The glass is recessed to reduce air noise. If the glass is flush to the height of the vertical wall of the pinchweld, then what occurs is, what I call, the “flute” effect. Like a flute that is played by blowing air over a gap in a tube, air flowing over a gap between the glass and the roof creates a noise that the occupant hears and complains about. When the glass is recessed in the opening slightly, the air is diverted by the wall of the pinchweld thus reducing noise complaints.

The recessed glass mounting is not new. Many of you remember the windshield gauge recommended by BMW many years ago. The early gauge looked very similar to the shape of the state of Nebraska. The template of the gauge was printed in the BMW service manual and was supplied to create a tool for use in windshield replacement. The “panhandle” portion was to rest on the roofline, and the lower border was used to measure the recessed decking of the glass. Its purpose was to reduce the chance of wind noise. Later, a more sophisticated gauge was produced for sale to their dealers and customers. It actually had measurements needed to be met.

If you are having trouble with an increase of noise complaints after replacement, try decking the glass lower than the height of the pinchweld wall by 1/8- to 1/16- of an inch. It may help to reduce those costly callbacks.

The introduction of the exposed-glass mounting has led to a paramount concern for installers not to damage the exposed pinchweld wall. If the pinchweld is damaged during installation, and priming exceeds the underside moulding weather mark, there is a real possibility that our customers will not like the look. This has changed the way we remove the glass and even introduced a new type of tool, the wire-out tools.

Many glass parts now are designed with an exposed edge. Some are exposed on all sides and some are only exposed on the top of the glass part. Some show the wall and the floor of the pinchweld, and others have an underside moulding that replicates the PAAS windshields of the past.

Let’s address the underside moulding installations specifically as it relates to bonding.

The underside mouldings are held in place with a strip of double-faced tape. It is applied to the inside surface edge of the glass. It is used, like all mouldings, as a decorative finishing touch. However, if the underside moulding is not taken into consideration during the installation process, the bonding of the glass to the body of the vehicle can be compromised.

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There are a couple of procedures that can improve the odds of safe bonding:

  • Bead application. Make sure, when applying your bead, that the tip of the “V” bead is perfectly perpendicular to the floor of the pinchweld. If it is pointing outwardly, it will make contact with the moulding and not the glass surface. This will not only create an unsafe bond but it will also cause a moulding appearance problem and a clean-up nightmare. If there is an acceptable variant in bead application, it would be that the bead be slightly tilting inward, but 90° to the floor is better.
  • Set the glass top first when possible and set the glass high. What I mean by that is to set the glass higher than the opening and then bring it down into position. In this way the “V” bead will catch the underside of the glass and not the moulding. As the glass is brought down, the bead is in position to safely bond the glass to the frame. The bead is pushed up against the inner edge of the moulding but on the glass surface and not on the moulding.
  • Apply the new urethane bead directly on the existing original bead. If corners are cut, or if the bead deviates from the original bead even slightly, the result is the bead contacting the moulding and not the glass surface. It also can result in adhesive oozing outward causing the moulding to pucker and appearance to suffer. You may need to slow the application of the bead to assure accurate placement. This is hugely important to the success and acceptability of the installation.

Exposed-edge glass does provide for an attractive appearance. It reduces drag for more fuel efficiency. However, it is a blind-set installation. We cannot see the bond being made. We have to depend on our bead configuration, size and position to assure proper bonding and leak-free performance. So, make sure you pay attention to the bead application and the setting procedure. We cannot afford to be sloppy in our procedures with these types of installations. There is no room for error.