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Could be either one.  I would dry everything off really good than take a piece of plastic and tape it right at the of the bottom below the rear window trim and cover the trunk with it.  You can then pour some water over the rear window and see if you are still getting water in the trunk.  If so I would pull the rear window and replace the gasket and foam tape and reinstall.  If still dry than your trunk seal is leaking.




"The only dumb question is the one not asked"

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If you do pull the rear window do not go back with the foam tape it sucks and leaks a lot. They used on the roof rail and about every one of them leaked. Best to just dress up the window opening, hammer and dolly spot welds and file or grind sharp corners off the opening and of course clean and paint if rusty. Use the non hardening 3-M windshield sealer not urethane.
If you are pulling I can get your more info on window. Also the rear tail light gaskets that Ford used sucked and held water and rusted out around the tail lights. If leaking there you might need new panel. Daniel Carpenter makes a much better seal for the tail lights. I have NOS Ford and will never use them.

When a man is in the woods and talks and no women are there is he still wrong??:P


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I am going to have to pull the rear window.  It actually moves when I press down on 2 of the corners, pretty sure water is getting under the window seal.

I've seen a 360 mustang article talk about using string as part I install but it wasn't clear what they did with it.  Another writeup on this site.  Still unclear.

Like the idea of not using close cell foam.   Do the windows just press in and hold, no sealer or "glue"?  No wonder they leak?

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The string is actually a cord or thin rope and  it is used only to put the window in.   Although David has been at this much longer than I have I believe you should use the foam.  There are a number of post on the foam subject. I helped a friend with a 72 put his in using only sealant and no foam.  We were able to move the window a little after is was in.  I know the sealant will set but I feel the foam provides a tighter fit while acting as a water seal also.  If you follow the directions and put the sealant as shown it should provide a leak free window.  The link on our site for a "how to install rear window" from 2010 does not work anymore. The below video is for a front windshield of a earlier year mustang but it uses a gasket and the installation procedure is the same.   It's not that hard to do. Just make sure you have a helper.

Mustang Windshield 1965-1968 Installation - YouTube

Edited by Kilgon




"The only dumb question is the one not asked"

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Urethane vs. Butyl Windshield Adhesive: Don’t Compromise Your Safety

« BackTeran Marsell | Published on January 13th, 2021


urethane vs. butyl windshield adhesive

There are many factors at play when it comes to your vehicle’s safety – too many for the average car owner to be able to keep up with. Of course, you want to make sure that you and your family are safe…

But if we are being realistic, we have no choice but to leave some of this to the mechanics and repair shops. And, when it comes to windshield replacement, safety is critical. Your windshield is what keeps you inside your vehicle in the event of a collision. It helps to anchor your passenger-side airbag and keep your roof from caving in if your car rolls.

The Importance of Having a Quality Windshield For Your Safety

You may not realize it but, right now, there are no enforced safety standards for windshield repair. That means that each and every auto glass repair shop can make their own decisions about what materials they choose. They may choose to use for the repair as well as the installation process.

If you are in a situation where you need to have your windshield replaced, you should always push to have it fixed to the exact same manufacturer standard. Because it came off of the car lot at purchase.

If you are not sure that is happening, you should consider finding another shop that can answer your questions and fix your windshield right. The best way to do this is to look for an AGRSS certified auto glass repair shop. AGRSS certificate is a kind of guarantee that the shop will take care of all of your auto parts.

Certification by the Auto Glass Safety Council is entirely voluntary. But the organization is committed to “developing and maintaining standards for the replacement of auto glass, educating and accrediting the industry. It is also committed to promoting awareness of the Auto Glass Safety Council Standard (AGRSS) to the insurance industry and driving public at large”.

Auto Glass Adhesives are not all created equal…

One of the most important elements of a windshield replacement is the adhesive used to keep it in place. Without this, your windshield cannot stay in place and keep you safe.

Urethane Windshield Adhesive

Urethane Windshield AdhesiveWhen your car goes into the shop to have the windshield replaced, the auto glass repair professional should be able to take you through the adhesion process in advance. He/she should describe how they will remove the old windshield adhesive, install a primer and then use auto glass urethane for the new installation.

The urethane must then sit after it is applied in order to cure properly and create a seal. This is very important to a successful and safe installation. A full 24 hour cure time is usually recommended.

Some auto glass repair shops cut corners when it comes to windshield application. This can lead to major problems and even injury/death if a serious accident occurs. One way that some shops cut corners is by using Butyl windshield adhesive instead of Urethane windshield adhesive.

Butyl Windshield Sealant

Buyl Windshield SealantButyl is not actually even an adhesive, but a windshield sealant. It does not cure or get hard after an installation, so it does not create a hard bond with the vehicle that urethane does.

It was widely used until the 1970s and is about one half the price of urethane. So, many installers continue to use it despite the fact that it is not as safe.

Be an informed consumer about your auto

So, if you have a chipped or cracked windshield that you need to get replaced, find professionals to do the job. Also, ask your shop if they replace it based on the manufacturer standards and whether they are AGRSS certified.

Also, ask if they use urethane as the adhesive and talk to them about how long they recommend the car (for curing) before it is driven. If the answers to these questions do not meet the standards outlined here, we recommend you consider finding another shop to install your windshield. Safety is the most important thing when it comes to your vehicle. Do not let your repair shop cut corners and roll the dice with your safety!

3M Auto Glass Urethane

We, as Team Acme professionals, use top quality materials for auto part repairs. Safety is the highest priority in our processes. We use 3m auto glass urethane as our auto glass urethane windshield.

If you happen to live in the Las Vegas area and are looking for windshield repair, you are in luck. Team Acme one of the only AGRSS certified auto glass repair shops in the area and is also home to the only master certified tech in Nevada.

We are committed to using only the safest products during installation and making sure that when your car leaves our job, it is just as safe as when it left the manufacturer. Contact us for more information about AGRSS Certification or request a quote for windshield repair today!

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Two different issues, one is setting stationary glass that uses weather-stripping that fits around both the glass and the pinch weld and the other is setting a windshield that does not use gaskets/weather-stripping.

Use only urethane for setting stationary glass that does not use a gasket/weather-strip, it is all that holds the glass in place.

Use butyl in conjunction with the gasket/weather-strip for water proofing the gasket/weather-stripping, the gasket/weather-stripping holds the glass in place, not an adhesive.

It's possible to set our rear windows in urethane, just like the front windshields, and do away with the gasket/weather-strip, you will just need to come up with something to hold the headliner in place. This link will show you what is involved (sorry about the GM stuff):

1960's - 70's GM A-Body Stationary OEM Installation Details - Belden Speed & Engineering - window channel rust patch panels, chevelle, rust repair, patch panels, GM a body repair



“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein


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I hate to see bad information. The foam used by the factory was junk. My car leaked two days after I picked up new. 2" of water in the back floor.
When you have a rubber seal a good seal is all you need but a little insurance is the 3-M non hardenging sealer. I have been using for over 50 years. It is called bedding compound and was made to use with rubber seals, glass and steel body. It takes a tiny amount of the bedding compound to work.
Pulling in windows with a cord has been around as long as there has been rubber seals nothing new. I have pushed the windows out with my feet and not broken. There are special tools for the corners to pull them through.
I cannot make a video I just found out today that along with my crushed disc I have torn rotatory cuff in my left arm.
You can use what you want but I stand behind getting the flange around the opening in great shape, break any sharp edges, coat in paint and pull the window rubber in with cord and apply small amount of the 3-M bedding and it works. My first car I did was a 1950 ford with rubber seals and bedding it worked in 1964 and works today. The foam tape was an attempt to clean up the assembly process but does not work. Even NPD states to not use the foam tape for the roof rail IT DOES NOT WORK.
CJ PONY  has a stupid video saying that you need three tubes of the bedding compound. I would be shocked to use 1/2 tube.
Your car do as you like but the foam is junk and for sure the urethanes are not made for rubber seals.


When a man is in the woods and talks and no women are there is he still wrong??:P


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