|01-06-2013 09:52 AM|
Well in cutting out windows in sixties cars I remembered it as being a very rubbery substance with a string thru the middle. Apparently it came on big rolls and they pulled it off the roll and put it on the glass before setting it at the factory. That apparently was a "damn" so the adhesive, a urethane "Like" substance that held the window in wouldn't ooze out into the passenger compartment when the glass was pressed in.
Here is what was posted on how it was done at the factory on a thread about window setting at the Team Camaro site. And can be found there...Setting glass - Butyl or Urethane? ... AAARG!!! - Chevelle Tech
"GM never used butyl tape or anything like it to install windshields or backlites. Period.
The body opening flange was coated with black silane primer using a flow-brush 30 minutes prior to installing the glass, and all the reveal molding clips were installed to the Body Shop-installed weld studs.
The glass was placed on a powered rotating fixture, inside edge up, retained by suction cups.
The glass periphery was cleaned using a solvent, dried, and a different silane primer was applied.
A fabric-reinforced self-adhesive foam rubber "dam" was extruded and applied to the glass just inboard of where the Thiokol adhesive would later be applied; the purpose of the "dam" was to contain any Thiokol "squeeze-out" so it wouldn't show from the inside past the edges of the interior garnish moldings after the glass was installed to the body.
After dam application, pumpable Thiokol adhesive (with a pyramid-shaped cross-section created by the dispensing tip) was applied adjacent to the dam, all the way around the glass.
Lower glass supports were fixture-located and screwed to the cowl, and rubber spacer blocks were glued to the opening flange. The spacer blocks set the height of the glass relative to the body to ensure a good fit of the reveal moldings.
The prepared windshield was removed from the rotating fixture, installed in the body opening, and pressed down against the rubber spacer blocks; wooden tonque depressors were used to "paddle" the Thiokol around the edges at a 45* angle from the top edge of the glass to the bottom edge of the body opening to ensure a continuous seal all the way around the glass.
Reveal moldings were installed.
That was the plant production process, and explains what is sometimes described as a "rope" being found when an original windshield is removed - the "rope" is the fabric-reinforced rubber "dam" that was applied prior to applying the Thiokol adhesive.
If you'll look in Section 4 ("Fixed Glass") in the Fisher Body Service Manual, you'll see exactly the same process for windshield replacement, except the "dam" wasn't included with the Service kit - masking tape was used instead to control "squeeze-out".
The Thiokol installation passed the Federal MVSS windshield retention tests, and contributed substantially to the body's torsional stiffness; it also helped the structure pass the roof crush test. It's illegal to replace a windshield with butyl tape, although some glass shops do it as a less-expensive short-cut method instead of doing the job right."
As I present in that threat at Team Camaro, these cars aren't unibodies and the glass is doing nothing but keeping water and debris out of your car. In a collision while driving a 1968 Camaro if your windows being set by urethane were to make a difference over butyl you are in BIG trouble and that glass attachment is the least of your worries. That being said, why not do it in urethane so there is NOTHING to think about. When I was setting windows on a regular basis on butyl, I was doing it without any training or understanding of what I was doing and I feel bad about that now.
It's like the old argument that you will get from people on the forums "I do it and it works", we all have heard that over and over. Well I set windows on lacquer primed, lacquer painted pinch welds with Butyl tape over and over, and they didn't leak. That didn't make it right! That was HORRIBLY wrong, now with a little education (that damn book learning) I have learned (and it makes sense) that was miles from proper. So I am building a car, I am sand blasting window pinch welds cleaning it all out. What is the difference from that point to do it right, epoxy primer over bare metal, then protect that from paint so you can set the glass on urethane over that epoxy primer, OR you paint the pinch weld and use butyl tape? The difference in how well that glass in mounted is HUGE, the difference in work or money or time doing it is next to nothing, so why not do it right?
Like I have said my Gran Sport has a windshield set on butyl tape, over epoxy primer. I feel, it's an old car I am screwed in a bad accident anyway, that is good enough for me. But it would have been just as easy (realistically) to install it with urethane. The urethane application learning curve is VERY steep though. Butyl tape is a sure thing home hobbiest level product. Applying urethane is NOT, yes it can be done but holy cow can it be screwed up too!
So a decision has to be made by anyone setting their glass, make it and live with it.
|01-06-2013 04:22 AM|
Maybe the ones I've seen (and the Camaro) were already replaced previously. Because they were rubber, not urethane. No mistaking one for the other. Mind you, the newest of these was the '81. Others older by a fair margin.
When did the OM quit using the sticky rubber, or are you saying none ever used it? Not arguing, trying to learn siomething.
|01-05-2013 05:50 PM|
You wouldn't leave butyl you are talking about urethane, or what the factory used which was like urethane basically. You cut a layer off the urethane with a razor to create a "fresh" urethane to apply more over before setting the window in. And of course this is when you don't have a reason to remove it all like to properly clean the pinch weld of rust or loose paint or what not. But you would never cut the butyl, that is a whole different animal.
As far as the urethane over butyl, it isn't for cars with air bags, there is no car made that I know of that used butyl on the windshield. It was common and I have done a crap load of them where I used butyl, 60's and 70's cars mostly. But as in any modern unibody the windows are a structural part of the body! So the urethane is bonding that glass to the body to make it a part of it. Butyl tape doesn't even come close to doing anything like that, it is VERY weak.
The only butyl used these days is in bolt in quarter glass and back glass applications in some vans and trucks. What they have is a plastic body around the glass, they call it "incapsulated glass". This plastic piece has studs sticking out of it that stick thru holes in the body at the window mounting area. The window is being held in by those studs and the butyl. Slider rear truck windows are often held in like this.
By the way, not that it means jack but I have an ICAR certification for glass, all it means is at one time I sat thru a class on this so I am repeating what I learned there.
|01-05-2013 04:20 PM|
I have only changed a single windshield, in a Camaro. I was told to leave a thin layer of the rubber in place, but only if I replaced the windshield at the same time I removed the broken one, so no dirt/contaminates could get on it (it will be sticky).
So that's exactly what I did. All I can say is it didn't leak, and I could see there was no rust (FL car). Guess I was lucky for once.
I was told at another time the urethane was more for vehicles that had air bags. Something about the urethane keeping the glass from popping out when the bags deployed. Hadn't thought of that till just now and no idea if that's true or what.
|01-04-2013 06:29 PM|
|01-04-2013 04:51 PM|
As long as you know what you are doing, I have seen too many cars destroyed by someone who didn't get it.
|01-04-2013 04:34 PM|
|01-04-2013 04:21 PM|
More often than not it did just the opposite, trapped water that couldn't leave, and rusted the metal. And if you haven't cleaned up out you don't know what is there. You don't plan on sand blasting the body do you? That is a serious NO NO unless you have piles of experience. You can do some SERIOUS damage to sheet metal panels. We are talking throw them away because they are ruined kinda damage VERY easily.
|01-04-2013 03:43 PM|
I have installed a windshield using urethane back in my auto body class I took in high school. I feel confident I can get this done.
|01-04-2013 03:33 PM|
Yes you MUST remove it all, leaving it would be a big mistake on a number of levels.
First off, there is GOING TO BE rust in that channel. I have done way too many of those GM window channels to count and I have NEVER, make that NEV-ER seen one that didn't have some rust that needed to be cleaned up and primed, and only a few with only rust, they most always have rusted holes. The clip studs are often broken, there is just no reason what so ever to leave that junk there.
Now the next decision, do you use the Butyl tape or do you have a glass shop set it in urethane? I have done a pile of those windows on butyl and it seems to work fine if you have covered all your bases. Some worry about the structual aspect, but realistically in my opinion this isn't an issue for a number of reasons. But your car did NOT come with butyl as I thought for years it did. It wasn't urethane either, I think kinda in the middle between the two as far as strength. But non the less, having a glass shop install your new windshield on urethane could be a good way to go. You can do it your self but the learning curve is pretty steep and I would say have someone do it.
Here is a "Basics of Basics" on setting glass. I added a disclaimer at the end warning about using butyl tape because I was getting such flac. But really especially on the back glass I don't see a big deal. But it is a choice for you to make.
"Basics of Basics" Window Setting - Team Camaro Tech
And you are going to want to sand blast your channels and apply epoxy primer by the way.
|01-04-2013 02:58 PM|
Do you guys leave the old butyl tape on when you change your windshield?
I been working on my Firebird. I am trying to get the body ready to be blasted. I just got done removing the front and rear windshields.
I used one of those windshield removal tools with the two handles and a blade.
Windshield Removal Tool - Speedway Motors, America's Oldest Speed Shop
The rear windshield came out fine, no damage to the glass. The front however was a real pain. The blade on the tool was not even long enough to cut through the mass of goo. I then tried the guitar string method which seemed to do the trick. Unfortunately the glass cracked on the edge while using the guitar string method.
When I removed the glass, there was so much butyl tape on the windshield frame that even the trim clips were buried under it. It is basically a mess of butyl tape. People must have just piled new butyl tape over the years without ever removing the old butyl tape.
I figured it was just some more poor quality work that has been done to my car over the years until I talked to this neighbor who swears to me that you should not remove the old butyl tape.
What you guys think?