How to: Quarter Glass Installation

Rktpwrd

Comic Book Super Hero
Supporting Member
Feb 2, 2015
3,329
113
Calgary, Alberta, Canada
Ok everyone, I’m doing this from a couple of requests to see a detailed account of how to install quarter glass in your G body after recently doing mine.

The following step by step procedure will pertain specifically to 1978-‘80 Cutlasses, but because many of the G models shared similar installation, you may still be able to use this as a rough guide for your particular application.

I had removed my quarter glass windows and associated trim and seals to perform some rust repairs on my ‘80 Cutlass. After the repairs were completed and the area was painted, it was time to reinstall the trim and glass. We’ll start the procedure from this point. The pictures I’m including are from my recent reinstall.

This is a relatively easy job to do, the best path to success is to take your time, be patient and methodical, and don’t rush things! If you follow these recommendations, you should have no trouble whatsoever.

To begin the reinstallation process, you need to lay out and evaluate the condition of all your particular pieces. If they’re all present and in good condition, the next obvious step should be a thorough cleaning of all the parts. The installation of dirty or damaged parts will only serve to negatively affect the end result. In my particular case, I had already cleaned the chrome trim that installs over the ledges where the windows will mount. However, on my car there is a molded seal that needs to attach to the trim as well.

Lay out the seal, and clean it up. A little Spray Nine or Fantastic general purpose cleaner and an old toothbrush work well for this:

D1735AF6-970F-4CB8-B0F5-F7BEE058CD39.jpeg


The seals on the 78-80 Cutlasses have these small tangs partially punched out. They’re usually already bent and standing up like this:

1528F829-4222-43E5-BE0C-46BFB129637F.jpeg


The fit of the seal to the trim will dictate what you do next. Originally, these tangs were designed to hook into holes in the trim, and then the trim and seal installed onto the car in one piece.

However:

It’s been my experience that these seals shrink slightly over the years. So if you install the seal onto your trim and find the shape doesn’t exactly match the inside of the trim, you may want to do what I did.

Using a small hammer, gently tap the tangs back flat and into their original spots:

44036D03-2DB1-4FA9-B2B2-6A18461A65A6.jpeg


Don’t worry about the seal not aligning to the trim, as you’re about to see the seals screw to the trim and the car in only one position anyways.

Once you’ve got the trim and seals ready to go, carefully install the trim next. On the 78-80 Cutlasses, this is done by carefully feeding the top of the trim underneath the driprail moulding and over the ledge, then gently lifting up on the trim enough to get it over the ledge at the bottom by the “B” pillar. Once the trim is over the ledge, firmly push down and back on the trim to fully seat it.

With the trim in place, now you can move onto installing the seal. Position the seal on the inside of the moulding, and attach it with 3 small screws. These screws go through the holes in the moulding and into the holes in the body. I changed the screws to ones with larger heads for more surface area.

Lower front:

16505812-7E69-4737-87E9-1CD05107B4F5.jpeg


Inside corner:

C396CFEB-8012-4053-B9B7-88D5DE9F4C06.jpeg


And upper top:

23B5459B-1103-4AB8-998E-2E00B365CE90.jpeg


It’s at this point where you want to move to the outside of the car and inspect how the seal conforms to the moulding. Manipulating them with a small hammer from inside the car can get them to fit nicely:

B2DD8C18-70A8-4BF3-8529-377D7FF9FA32.jpeg


C09574F3-C795-4F13-885E-A5F94F61F562.jpeg


C1BE3282-ED5C-443B-A0F4-949EDA7EA818.jpeg


Back inside the car, you’re gonna have to spend some quality time removing all the old butyl (that sticky black crap that everyone loves so much).

Various people have come up with and had various levels of success in finding ways to effectively remove the old butyl, my suggestion is to use whatever means works best for you. I personally had moderate success by starting with a small ball of the old stuff and using that to get what I was trying to remove to stick to it. Either way, I recommend removing as much of the old stuff as possible ahead of time.

Next it’s time to do a test fit of the glass to the seal. It’s your last chance to correct any fitment issues before the glass goes in permanently. If you’re satisfied with the fit, you can proceed onto installing new butyl.
I picked up a box of Proform brand butyl tape at my local auto parts store, 3/8” diameter for around $20:

BD237BDD-B8DD-48CE-858C-275E89E3BBD8.jpeg


Thoroughly clean your glass inside and out, and make sure there’s no remnants of the old butyl on there. Residue can be cleaned up with wax and grease remover.

Starting at the top middle, start laying the new butyl on the OUTSIDE face of the glass. I recommend starting the strip at the top of the glass as you’re far less likely to have water leak by here than anywhere else.

Keep it as close to the edges as you can. You’re going to be compressing this stuff when you install it and you don’t want to see any of it squishing out the sides.
Work your way around the perimeter, and meet back up to your original starting point. When you cut the butyl, cut it slightly long so you can overlap the ends.
No gaps this way.
When you’re done, your glass should look something like this:

FB4C4EA2-474A-46B5-91E8-9E047A667662.jpeg


If you have one from the disassembly, position the black plastic spacer on the ledge just below the seal. It doesn’t actually stay there permanently, it’s just to position the glass at the correct height when you go to lay it in. You’ll see why in a minute:

2BE72206-FB2C-46F2-89A1-74DC6233921C.jpeg


Next carefully and gently lay the glass into place paying particular attention to the edges. You don’t want it touching the sides of the body anywhere, you want it centered in the opening as best as possible. The bottom of the glass should rest on the spacer you just set in place.

There are two clips that you should install next. Hopefully yours are intact and didn’t break upon disassembly. The short fatter ones go on the back edge...

D441FF7F-B5BC-46B8-B11F-3BE5E4504FB4.jpeg


...and the longer skinnier ones go on the front:

E9ED118A-FCBD-4D58-8E0C-A2991FC45B35.jpeg


Gently push them in until they snap into the body. Their only real purpose is to hold the glass in place until you can install the upper and lower clamps.

Now install the lower clamp. It has a ledge of its own that the glass rests on, so that’s why the spacer is needed; to give you the room to manipulate the ledge of the clamp under the glass. Then snug down the screws and remove the spacer.

Lower clamp:

92D1233F-9414-416D-801A-BF781E002A55.jpeg


Time to install the upper clamp. The top hooks into the body and provides leverage against the glass as you tighten the screw down. Again, only snug up the screw at this point.

Upper clamp:

4D212064-F762-45B6-90AB-7508E2DD584E.jpeg


Now, using the flat of your hand push as hard as you can along the outside perimeter of the glass where the butyl is. The more pressure you can apply here, the better it will seal. DO NOT use the clamps to do this! They will only apply pressure at the top and bottom of the window, and will likely bottom out first anyways.

Use the pressure from your hands to seat the butyl, THEN tighten up the clamps. Use your discretion, if it feels like you’re tightening the clamps too much, then you probably are.

You’re nearly done. There’s a couple of spots visible from outside the car that may leak on you if they’re not sealed up. A little left over butyl trimmed and manipulated into these areas will seal them off:

ABD5428F-B554-4642-A147-EC748D8B3583.jpeg


4318B8DF-BE9B-4088-9807-5E9018BE2F38.jpeg


Here was the finished install on my car:

8C390548-C858-4ABF-9600-892487F9BD38.jpeg


BCADF0E8-EAB2-4135-9A78-759C6B462DD5.jpeg


I strongly advise giving the glass and new butyl a couple of days to take a set and settle in, then give it a thorough water test before reinstalling the rest of your interior. You don’t want to find a water leak afterwards!

And that’s all there is to it. Hopefully this is of use to others for years to come.

Donovan
 
  • Informative
  • Winner
  • Like
Reactions: 16 users

old80cs

Master Mechanic
Jun 27, 2013
373
93
Massachusetts
Thanks, Donovan!, I appreciate your time and effort in documenting the installation of the windows.
 
  • Like
Reactions: 1 users

Rktpwrd

Comic Book Super Hero
Supporting Member
Thread starter
Feb 2, 2015
3,329
113
Calgary, Alberta, Canada
Thanks, Donovan!, I appreciate your time and effort in documenting the installation of the windows.

You’re very welcome Mike.
:)
 
  • Like
Reactions: 1 user

79CutlassSupreme

Not-quite-so-new-guy
Sep 21, 2014
10
3
Wichita, KS
Wow! I've really been enjoying the read and learning a ton from your build threads. This is one of the areas I really need to address, so thank you for doing this write up.

I have not been able to find new seals for the quarter glass, and mine are pretty much non-existent on the '79. Would you happen to know where to get these or have an idea for a suitable substitute?

Again, you do amazing work and your attention to detail is inspiring.
 
  • Like
Reactions: 3 users

Rktpwrd

Comic Book Super Hero
Supporting Member
Thread starter
Feb 2, 2015
3,329
113
Calgary, Alberta, Canada
Wow! I've really been enjoying the read and learning a ton from your build threads. This is one of the areas I really need to address, so thank you for doing this write up.

I have not been able to find new seals for the quarter glass, and mine are pretty much non-existent on the '79. Would you happen to know where to get these or have an idea for a suitable substitute?

Again, you do amazing work and your attention to detail is inspiring.

Thank you very much, glad you found the write up useful. That’s justification enough for me to have done it.

Unfortunately the seals are no longer available through GM, and despite my and a couple other members efforts to get the aftermarket to step up to the plate, no one is currently making them there either. Pretty much your only option at this point if yours are nonexistent or beyond reusing, is to try and locate a decent used set. This can be tricky I know, as the surviving pieces are all over 40 years old at this point.

Depending on how creative you are and what you can find that’s similar to the original seals, you might be able to put together a suitable substitute. If you manage to come up with something that works, post it back here so that we all can benefit from your solution.

Good luck.

D.
 
  • Like
Reactions: 1 user

79CutlassSupreme

Not-quite-so-new-guy
Sep 21, 2014
10
3
Wichita, KS
Thank you very much, glad you found the write up useful. That’s justification enough for me to have done it.

Unfortunately the seals are no longer available through GM, and despite my and a couple other members efforts to get the aftermarket to step up to the plate, no one is currently making them there either. Pretty much your only option at this point if yours are nonexistent or beyond reusing, is to try and locate a decent used set. This can be tricky I know, as the surviving pieces are all over 40 years old at this point.

Depending on how creative you are and what you can find that’s similar to the original seals, you might be able to put together a suitable substitute. If you manage to come up with something that works, post it back here so that we all can benefit from your solution.

Good luck.

D.
I was afraid of that... thank you for the info!

I've only found one other pair in the wild at a pick-a-part on a '78 and they were just as bad as mine. I have been all over the Steel Rubber catalog and a few other aftermarket weather stripping/rubber companies looking for something similar enough to take a chance on ordering to no avail, but I'll keep looking and will definitely pass that information along when I find it!

Keep up the great work and thanks again for sharing your knowledge and experiences in such detail with all of us! It is greatly appreciated!

Thanks!

James
 
  • Like
Reactions: 1 users
G-Body Performance Upgrades

GBodyForum is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com. Amazon, the Amazon logo, AmazonSupply, and the AmazonSupply logo are trademarks of Amazon.com, Inc. or its affiliates.

Please support GBodyForum Sponsors

Classic Truck ConsolesDixie Restoration DepotMike's MontesP-S-TSouthside Machine PerformanceUMI Performance

ContactAdmin@GBodyForum.comfor info on becoming a sponsor