GPS Windshield Mounts That Hold

Many of the automotive GPS units by Garmin include a windshield mount. The mount attaches to the glass with a round, plastic suction cup. While the design is a good one, the grip will eventually fail and the unit will suddenly fall onto the dash. The good news is that this is an easy problem to solve.

The cause is ultimately microscopic, or nearly so. The suction cup is just a piece of thick vinyl, shaped like a small bowl. When pressed against the glass, with the locking lever pushed into place, the center of the bowl is pulled up into the mounting bracket slightly, creating a small vacuum in the bowl. As long as the rim of the bowl seals against the glass, the mount will remain firmly attached.

When the mount is new, the surface of the plastic is smooth and shiny. The seal is good and the mount sticks. However, as the plastic ages, its surface becomes very slightly roughened and dull. Take a look at the photo of a mount that is about a year old. The darker grey ring is where the seal presses against the glass. Any place the seal is not actually touching the glass, the color is very light grey. Even at this slight magnification, you can see that the seal is not the greatest. There are numerous light grey spots within the darker circle. By the way, the numerous bright specs in these photos are pits in my windshield, a consequence of driving Colorado highways.

The next photo more clearly shows the problem. Note how the contact area appears to be thin and diffuse. Each of these thin areas contains voids filled with air. If there is a continuous path from the outer edge to the inner edge of the dark ring, then air can travel along that path. Each path is like a tiny leak in an inflated balloon. Eventually, the balloon will deflate and go limp. With the suction cup, the air leaks will eventually fill the suction cup bowl with air, eliminating the vacuum, and the mount will fall off the glass. My one year-old mount used to fall off within 15 minutes of reattaching it.

Fixing this requires applying a very small amount of silicone grease or Armor All to the edge of the suction cup where it presses against the glass. A very thin layer of grease will fill up all the tiny voids and prevent the air from destroying the vacuum. Use a tiny amount, really. A dot the size of a pinhead is sufficient. Just spread the grease around the flat rim of the suction cup. Run your fingertip around the rim several times to spread the grease out into a thin film. If the grease is so thick that you can see the thickness of it, that is far too much. Wipe off the excess until there is just a barely visible streak on the surface of the plastic.

Clean the glass with a glass cleaner, or a soft, damp cloth. Now, reattach the suction cup to the glass. You should see a very different, dark circle. The voids will be gone. This photo shows the same mount as above with a very thin film of grease. Notice how dark the circle appears. It is thick and uniform in color, indicating a seal that is good enough to hold for months.

You might be tempted to use something other than silicone grease – something like axle grease, engine oil, 3-in-1 oil or petroleum jelly. Do not. All of these lubricants are petroleum-based. They are very likely to harm the plastic suction cup and speed its breakdown.

As I mentioned above, one alternative to silicone grease that is safe, and might even be better is a product called Armor All. This product is a specially formulated protectant. It is designed to preserve plastics and rubber by blocking ultra-violet (UV) rays. Since the mount is intended for use in a car, protecting the plastic from UV would be a good idea. And immediately after applying Armor All, there is a thin, lubricating film on the surface of the plastic. This is exactly what we want to form a good seal. Using Armor All on the suction cup not only keeps the mount firmly in place, it protects the plastic against degradation.