I have taken the rear glass out of my 70ss and need to reinstall it. My car has just recently been painted, and the guy didn't do a good job repairing the window channel, there were a couple of pinholes. I have filled the holes with POR epoxy putty. The rest of the channel has body filler and painted metal. The body filler is not perfectly smooth. Will this cause problems with the window sealer? I want to use butyl tape and do it myself, but I dont want it to leak. If I use the butyl, do I really need the pinchweld primer? Would it be worth it to have a pro do it with urethane for $65? Please give me your suggestions.

Joe

I haven't had too much experience with butyl, but i would say go with urethane regardless. The pinchweld primer is not used for adhesion, only for rust protection. I'm only aware of butyl being used for flat glass these days.

The glasses were originally installed with butyl and is the preferred installation method by restorers and professional installers. It's much easier and is a neater method.
However, I have been down the road you are, dealing with a channel that isn't straight and even and the only way you will get a seal is to use the urethane.
I think you pretty much know the answer, otherwise you wouldn't be on here second guessing...go ahead and call out a professional installer, let him make the professional decision. Then, if it leaks, he should stand behind his work and correct the problem.

Shannon

I use the primer even with butyl tape. Put your rubber blocks down with the drain slots down in the bottom of the gutter. Put your tape down and set the glass in. Push it from the center of the glass to set it and look around the edge to see how your seal is doing. If you have any spots that haven't sealed, take a paint stick and push the butyl in that spot better. When your satisfied with your work go get the hose and check it for leaks. If you find one, get the paint stick out again. You can run a bead of sealer around the top and sides in addition to the butyl if you have leak problems or for added insurance.

I used Butyl Tape and the pinchweld primer on both the front and rear windshields of my 68 El Camino and the rear windshield of my 68 Chevelle and nevr had any problems. This was the way they did it back then when these cars where new and look how long they lasted!! Id say that was pretty darn good. So why wouldnt it be good enough to do still today and have it last another 25-30+ years ?? The Butyl and pinch weld primer is the only way I will go!!!
Mark -------------------------------------------------------------------------------------------------------------------1968 El Camino -1968 Chevelle Malibu

New glass has a "blacked out" area that hides the urethane, so it's not as critical how it squishes out. Older glass doesnt' have that area so you'll see an uneven area around the glass. Other then that they both do the same thing. I used butyl BTW.

David

As the above post mentioned, the blacked out hides the urethane but more importantly protects from the UV light. That blacked out area around modern day glass protects the urethane from breaking down from UV light. Your chevelle glass does NOT have that. And over time that urethane WILL break down.

Pinch weld primer is for corrosion protection AND adhesion.
Ever see an urethane installation without that primer applied first? You can peel that urethane right off!!!
If you can peel the urethane right off the pinch weld you did something majorly wrong...Eric

When you replace the glass you put primer on the glass which is black and creates a black out mask for uv protection. Just replaced the glass in my 70 El Camino and I used urethane, 65.00 is a good price considering all, but make sure they space out the glass properly so the moldings fit. I used 3/16" spacer blocks.

IM getting ready to do the same thing with both windows. But my rear window channel is rusted out. Weve decided to go with a fiberglass filler for the rear and use screws for the trim studs. I think im gonna go with the butyl and then seal around it good with some silicon.

I have used butyl for 3 windows, 2 front and one rear. I works well, but I did use the primer first before I laid down the ribbon.
On my 69 cutlass, someone before me installed the rear window with urethane. It squeezed out all over the place, and I can't get it off because there is no room on the inside of the car on the bottom by the package tray to get at it. Hence, I will remove the window some day and install again with butyl. Butyl doesn't squeeze out like urethane calk if you press down too much.
Here is a tip I learned from a corvette magazine. Lay the butyl tape on the window frame. BEFORE you lay the glass against it, go around the outside edge of the butyl tape with the urethane calking gun and squeeze some urethane against the butyl ribbon. Paddle the urethane which is nice and soft tightly against the butyl. You will then have a leak free seal. THEN push the window down on the tape.
You have to put the urethane calk in place before you put the glass down because usually there is not enough room to fit your calk gun tube against the butyl tape after the glass is down. I did this once and it worked fine.

If you want original looking, go with butyl. Must be 5/16" on the rear window if you want the moldings to fit right. There probably are pros that do a nice job with urethane but I've also seen some nasty looking jobs with it that really jump out at you. No doubt it seals out the water but butyl looks the best and most original. Maybe the butyl/urethane combo mentioned by bhawk is a good alternative. I've never had any leaks with just butyl myself. As mentioned, you can tell by looking through the glass at the strip if you have any gaps in the seal.