by Bob Beranek
  • facebook

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 next series of articles are going to be what I call the “versus” articles.  I wish to share my opinions in regards to different ways of doing things, different tools over another and different products over others. This, I suspect, will be a controversial discussion because everyone has their own likes and dislikes. Today I wish to discuss a subject that has been a debated over several years and several beers—the difference between applying urethane to the glass versus the pinchweld.

What is better?  The answer is neither and both. There are pros and cons to both methods of application and it is the reason I teach both in my classes. Both methods can be accomplished safely and properly, but each has problems to overcome.

Applying urethane to the glass
It is very important that the newly applied adhesive bead be matched up with the newly exposed existing bead for optimum bonding and adhesion.

Pros

  • It’s the way the OE does it.  It is true that all vehicle manufacturers apply the adhesive to the glass.  Why?  Because they use robots to apply the urethane and to set the glass.  It is easier to program and apply a liquid to a smooth solid surface.  Plus, the urethane does not need to meet an existing bead for adhesion.  If there is no existing bead it creates its own.
  • There are fewer seams. Being able to walk around the perimeter of the glass does allow for one seam—where you started is the place you will finish. There will be fewer areas of possible leaks because there are fewer seams to paddle.
  • The application is more pleasing to the eye.  The use of guide posts built into some of the urethane tips and/or the skilled guidance by a competent technician will most definitely improve the appearance and placement of the finished bead.  Plus, the smoothness of the glass allows for a clean continuous bead with no bumps or interruptions.
  • It forces the technician to use vacuum cups.  If the technician applies the adhesive to the glass edge, it is very difficult to set the glass with one’s hands because of the mess factor.  The tech is almost driven to set the glass with cups and with an exposure to the bottom pinchweld, which would require pulling the cowl panel.

Cons

  • Recessed beads must be measured out. Any recessed beads found on a particular vehicle, whether top or bottom, must be measured out on the glass and marked for application. The new bead must match up with the newly exposed existing bead to assure the best adhesion.
  • The setting of the glass must be precise. Due to the fact that the new bead of fresh urethane is hanging from the underside of the glass as it is set, it must be set exactly right or the urethane will touch the interior moldings or opposite “A” pillar and not only make a mess, but disfigure the bead and cause bond and leak problems. It would be highly recommended that a second person or a setting tool be used to assure placement in the opening. It would be further recommended that a dry set procedure be utilized to assure placement.
  • If the pinchweld is uneven, the chance of leaks is increased. Where the new bead is applied, if applied correctly, is the most likely area to be leak-free because it is able to be observed. Once the glass is set, it is out of the technician’s direct line of sight. If the pinchweld is uneven and the bead fails to touch the existing bead, gravity will channel the water into the vehicle. This is because the unseen uneven surface is lower than the surface you applied the urethane to—the glass.
  • There may be more primer usage.  It may be necessary to apply an extra amount of primer around the existing bead to guard against the new bead missing the existing bead. If the new bead misses the existing bead and touches unprimed painted metal, the bond may not be strong enough to meet the safety standards mandated by government. This extra primer will be an extra cost that must be incurred.
  • It may mean longer installation times. The addition of time to make measurements of recessed beads, dry setting the glass, setting up a setting tool, and priming around the existing bead may mean that a few extra minutes are consumed to do the job right. To some it is well worth the cost in time and materials to others it is not.

Applying urethane to the pinchweld

Pros

  • It is easy to follow the “roadmap”. Once the glass is out and the urethane is trimmed down to the proper height, it provides a perfect roadmap by which to apply the fresh urethane bead. Just apply the urethane directly on top of the existing bead and it is the right place to put it. Applying the new bead to the existing bead allows for an application that fills the uneven surfaces better.
  • Handling the glass is easier and less messy. There is no urethane hanging down from the underside so it will be easier to handle a small chance of a mess.
  • No chance of missing the existing bead. Applying the urethane directly to the existing bead eliminates the chance of missing that bead. There will be no need to measure and mark the new glass for installation. 
  • The only priming you will need is that which covers scratches. There is little chance of missing the bead so extra priming in unnecessary.
  • The chance of leaks at the bonding surfaces is reduced. The urethane is applied to the existing bead so the meeting of the two beads is assured. The only question left is in regards to the meeting of the adhesive and the glass surface. The beauty of a “V” bead is that as long as the tip of the “V” touches the smooth surface of the glass, it is sealed and bonded. Plus, gravity channels the water away before it reaches the glass to urethane bond.

 Cons

  • More seams means more chances of leaks. The only way to apply urethane to the body and have only one seam is to have a very small car or a very tall technician. It will be necessary to take care in paddling the seams caused by application. There are techniques that reduce the severity of seam gaps, but there is no way that there will not be more seams to deal with.
  • The sightline to the customer may be a problem. It is very possible, unless you are dead steady, that your bead will not be smooth and straight. This will cause the customer, unless you apply a dam every time, to see the shiny black goop that may be oozing into their vehicle.
  • Care must be made in positioning the bead on the existing bead. The new exposed edge glass demands the bead positioning be perfect to eliminate the urethane from being visible to the customer. It also must be placed properly to eliminate the clean up after the install.
  • It does not keep the technician from setting and dragging the glass. How many of you set the glass and then move it forward or back to position it in the opening? I’m sure you have. You must stop that. The glass must be set within a ½ inch either way or you run the risk of displacing the bead and causing bonding leak problems. The glass being on the body instead of the glass spoils the technician and is likely to drag or pull the glass.

As you can see there are a number of pros and cons to application procedures and how you choose to apply your adhesive is entirely up your level of comfort and confidence. There is no right or wrong way. There is only your way. Just make sure you keep in mind the “cons” to your method.