Exposed Edge Glass 4 

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.