Know How Notes: How to Remove and Install Flat Glass Windows

If the windshield is cracked on your modern vehicle, you call the glass shop and have them come out and replace it for you. The process is messy and complicated, requires special tools and glues, and the glass is expensive. If they break it while it is being installed (which happens more often than you might think), they replace it on their dime. This makes glass replacement a lot more difficult for the average DIYer, but what about older vehicles, pre-1960s? These cars have flat glass and are typically retained with a weatherstrip seal instead of being glued in like most mid-60s and later vehicles. If you are considering tackling this project, here’s a few tips on how remove and install flat glass windows.

The process of restoring or customizing a classic car often requires you to remove and install flat glass windows and weatherstrips. This job can be intimidating if you have never dealt with glass before. It really is not as hard as it may seem. The key tips that will make the job easier and successful are patience, technique, and using the right tools.

Types Of Glass Seals

This style of glass is not glued in, rather held with a rubber weatherstrip. This style was used as recently as the late 1980s on GM trucks, but for the most part, glue-in glass has been the norm since the mid 1960s. There are two style of rubber-retainer: solid rubber and locking strip. The locking strip style (such as GM trucks 1989 and older), have a large outer weather strip that goes on the window and the window channel, with a smaller insert ring that presses into the a groove around in the center of the rubber. This pushes out on the retaining seal, locking the glass in the vehicle. You can remove the center ring and then cut the rubber to pull the glass out. After 30 or more years, the rubber is hard and brittle, these are rarely savable.

Removing The Glass

For the solid rubber seals, you just have to cut it. In most cases, you can use a razor knife and cut the outer lip off the seal and remove the glass. Sometimes you need to use a wire cutter, which is pushed through a section of the rubber and then pulled back and forth around the window, sawing through the seal.

Once the glass is removed, the area around the seal on the body of the vehicle must be cleaned and restored. Any rust and scale should be removed, holes need to be repaired, etc. If the vehicle is being painted, the glass remains out until that is completed.

Installing The Glass

Now the fun part begins. New rubber is soft and pliable, but windshield weatherstrips and seals are not the easiest to work with. These tips and tricks will help save your sanity, as well as your fingernails.

For a standard non-locking ring type seal, install the rubber onto the glass. This is fairly simple design, which can leak. It is a good idea to put a thin bead of weatherstrip adhesive inside the glass groove before installing the seal to the glass itself. These types of seals are usually fairly deep, so the rubber tends to stick on the glass before it is fully seated. Most 1950s and older vehicles have two-piece windshields, so a helper is very handy, as the glass can flop around while you are working on it. A suction cup handle  or two really helps keep thing in control.

Now that the glass is in the seal, there is an old-school trick that makes this job 100 times easier. If you try to use your fingers to flip the outer edge of the rubber seal over the window frame, you will spend hours trying and probably end up peeling back a few fingernails. Instead, loosely wrap a single cord around the outer seal groove, leave the two ends running out in the middle (criss-cross them for the best results). You can tape the ends to the glass so they don’t fall out while you position the glass.

Generously lube up the window frame and the rubber seal with lube. Don’t be stingy, it will help to have more than less.

With the glass in position from the outside of the vehicle, have your assistant carefully press the glass towards the interior of the vehicle, while you sit on the inside. Slowly pull the cord at a 90-degree angle to the glass. The rubber seal edge should pull into the cab, and as you work around the glass, the lip should slide into the seal’s groove. Once you reach the other end of the cord, the glass should be fully installed and ready for clean-up.

If your seal has a locking ring, follow the same steps, but the glass installs from the inside of the vehicle to the outside (pull cord towards the hood), and then lube up the locking groove and locking strip, and install.

Installing flat glass is not difficult if you use the tips and tricks shared above. Judicious lubrication and patience are the keys to a successful installation. Of course, if you don’t want to try this yourself, visit the experts at your local NAPA AutoCare Collision Center.

Check out all the vision and safety parts available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to install flat glass windows, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.