How to remove and install flat glass windows

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.

A razor knife is the best way to cut the seal on the glass.

A razor knife is the best way to cut the seal on the glass.

 

The older the rubber, the harder it is to cut, as this vehicle required using a screwdriver to break the hardened rubber away.

The older the rubber, the harder it is to cut, as this vehicle required using a screwdriver to break the hardened rubber away.

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.

A clean sealing surface is paramount to a leak-free installation.

A clean sealing surface is paramount to a leak-free installation.

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.

Before loading the glass into the rubber, add a small bead of <a href="https://www.napaonline.com/en/p/MMM08011?cid=social_blog_062018_glass" target="_blank" rel="noopener">3M weatherstrip adhesive</a> to help seal the rubber to the glass.

Before loading the glass into the rubber, add a small bead of 3M weatherstrip adhesive to help seal the rubber to the glass.

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.

If your glass has corners, like this two-piece windshield, start at one corner and work the glass into the channel.

If your glass has corners, like this two-piece windshield, start at one corner and work the glass into the channel.

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.

The trick for this type of rubber is to use a rope. Any strong rope will do. We are using <a href="https://www.napaonline.com/en/p/BK_7704381?cid=social_blog_062018_glass" target="_blank" rel="noopener">paracord</a> in this instance, but <a href="https://www.napaonline.com/en/p/SME704554?cid=social_blog_062018_glass" target="_blank" rel="noopener">string trimmer line</a> is also a great option.

The trick for this type of rubber is to use a rope. Any strong rope will do. We are using paracord in this instance, but string trimmer line is also a great option.

 

Start by pushing the cord into the rubber channel. You may want to use a flat bladed tool to help push the cord deep into the rubber.

Start by pushing the cord into the rubber channel. You may want to use a flat bladed tool to help push the cord deep into the rubber.

 

Next, apply some <a href="https://www.napaonline.com/en/p/MMM08011?cid=social_blog_062018_glass" target="_blank" rel="noopener">3M weatherstrip adhesive</a> to the window frame.

Next, apply some 3M weatherstrip adhesive to the window frame.

 

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

We used a homemade tool to hold the glass using suction cups. You can also use a couple of helpers.

We used a homemade tool to hold the glass using suction cups. You can also use a couple of helpers.

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.

Make sure the glass is even with the body and that the cord does not come out. Use a lot of soapy water to help this process go smoothly.

Make sure the glass is even with the body and that the cord does not come out. Use a lot of soapy water to help this process go smoothly.

 

With a helper pushing on the glass from the outside, carefully pull the cord so that the rubber flap pops through the car and around the sheet metal lip.

With a helper pushing on the glass from the outside, carefully pull the cord so that the rubber flap pops through the car and around the sheet metal lip.

 

In tight spots, you may want to use a nylon trim tool to help guide the rubber.

In tight spots, you may want to use a nylon trim tool to help guide the rubber.

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.

All done! This is a simple task but without the cord, you would be extremely frustrated and it would take much longer to complete.

All done! This is a simple task but without the cord, you would be extremely frustrated and it would take much longer to complete.

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 16,000 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.

about author

Jefferson Bryant

A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.

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