Here's how I do it. Wrote this narrative last time I did one. Hope it helps you.
C-1 Corvette Windshield Replacement (never let fear and good sense hold you back)
Replacing the windshield on an older Corvette is probably one of the most feared and intimidating jobs you will ever perform on your older Corvette. If you have patience and a modicum of mechanical aptitude you too can perform this task in a professional and rewarding manner.
Myth Ė You can change the windshield without removing the whole assembly from the body. Well, almost a myth. It can be done but not without breaking the tabs off of the lower windshield posts. This was reportedly a fairly common practice in glass shops where flat rates were charged and quality of work was not one of their strong suits. In short Ė To do the job right without destroying anything, you must remove the windshield assembly from the body completely.
It really helps to be young and limber as you have to lie on the floorboards in a contorted position with your head and shoulders underneath the dash in order to remove the nuts which hold the windshield frame to the cowl. There are a total of 12 nuts which hold the windshield frame down to the cowl. The two outermost on each end are larger than the rest and secure the end posts to the cowl. There are two tabs (one per post) that are a part of the end post casting. The center u-channel is screwed to the end posts through these tabs. These are what you will frequently find broken. After you get all the nuts loose, enlist the help of an assistant and gently rock the windshield to break the bond with the cowl. In the two times I have done this on my car, the paint was not damaged as the u-channel rests on a rubber cushion strip and this is normally the point of separation. When you get the windshield assembly off, set it on a clean, flat, well lit, padded work surface. A couple of sawhorses with a sheet of plywood on it or an old door work well. Cover the wood with an old blanket for padding. Congratulate yourself and go have a cold beer! While you are having that cold beer you can assemble all the necessary tools, put on some soft music, and re-read the instructions. Before you start disassembly, take a magic marker and mark the centerline of the glass and the weather-strip at top and bottom, Also mark (on the glass, and on the weather-strip) the points where the end posts join the upper and lower channels. This is very important because once it is apart it is much more difficult to find these points accurately. Knowing where they are makes assembly much, much easier.
I did this job the first time about 30 years ago (when I was young) and then again last summer because the rubber around the windshield had become severely cracked during that time. The first time I was limber and impatient, the second time I was not so limber but much more patient. The net result both times was the same in that the job was accomplished successfully. The only difference was the first time it involved more mental anxiety and the second time it involved more physical pain. Iím thinking that Iíll be gone before it needs it again.
Over the years Iíve heard quite a few stories of breaking windshields in the process of replacing the glass. Fortunately I have not experienced that disappointment. It is important to have a good flat sturdy area to work. As noted above I used a couple of sturdy sawhorses with a sheet of thick plywood and then covered with a blanket for padding. This allows you to move all around the windshield without having to flip or turn it so much. I did the job by myself but it would be a help to have someone to help hold things in place in the assembly process.
One thing that makes things a whole lot easier is if before disassembling the windshield you take a felt pen and mark the center of the glass and also the location of where the wider part of the weatherstrip which overlaps the dash pad ends at each door post. Since the weatherstrip is so stretchy and it is hard to measure a centerline on the glass once the posts are removed, it is much easier if this is done prior to disassembly. If you are like me, I neglected to do this (both times) and had to do it the hard way.
Trial fit: You will notice that the part of the weatherstrip that lays against the dashpad has a wider lip than the rest and you want this to be centered on the glass and also to be stretched just the right amount so that the wider lip goes from end post to end post. If you take the lower channel and lay it up against the glass and then slip on the end posts (helps to have a friend here) and then take a felt tip marker and after centering the assembly on the windshield mark the glass at the intersection of the end posts and the lower channel on each end. Also mark the glass at the upper end of the windshield posts where they intersect the upper channel. Now take them off again and measure between the two upper marks and mark the centerline of the glass. Now take the weatherstrip and pull it out straight and measure to find the centerline of the upper part of the weatherstrip. This way when you assemble it you can line up the centerline of the weatherstrip with the centerline on the glass and avoid having to take the whole thing apart again because the weatherstrip is off center. I used sealant on my windshield inside the weatherstrip but a lot of guys say not to. I drive long distances sometimes and have gotten caught in rainstorms on many occasions. With the sealant I have never had a leak around the glass. It does make it a lot more challenging though with the sealant as it can be very messy. I used black windshield sealer in a caulking tube which I picked up from a glass shop. If you go this route make sure you get a quart of the windshield sealer cleaner to remove any excess which oozes out in the process.
Assembly: Use some silicone spray and spray the inside of the upper and lower windshield channels as well as the inside of the grooves on the end posts. This will make them easier to install on the rubber later. If you use sealer have your helper hold the weatherstrip open while you lay in a thin bead of sealer right in the bottom of the groove all the way around. Now make sure you have everything facing the right direction and carefully install the weatherstrip on the windshield taking care to line up the center marks at the top and then you can stretch the bottom as required to make the ends of the dash lip come out to the marks you put on the glass at the end posts. It should actually go a little past where the end posts meet the base channel on each side. With the sealer on it makes the whole windshield rubber want to move around easier and if it is not held in place can actually pull itself off. Avoid letting this happen as it makes a mess with the sealer all over. Now center and position the lower track on the windshield rubber and press into place. Be sure that you have installed the t-bolts in the base channel first. I used some windshield sealer to hold mine in place and let it cure prior to assembling it on the windshield. It helps to keep things from falling apart in the process. Next install the upper channel, centering it on the windshield between the two marks on the glass, and push it into place. Make sure the screw plates are still in place and then assemble one side frame and then the other and install the screws loosely till everything is started and lined up. A rubber mallet can aid seating the channels and end frames but avoid getting to rambunctious here as it is easy to break the glass. Check carefully to make sure that the weatherstrip is fully seated in the lower channel and that it looks even and there are no gaps at the glass. If something needs adjusting, now is the time to pull, tap, and tweek as needed. When everything looks good, snug up the screws at the top channel and lower channels. Now you will undoubtedly have sealer on the glass and on your hands etc. Here is where the sealant remover comes in. It works really good. DO NOT USE ANYTHING ELSE SUCH AS LAQUER THINNER etc. It will damage the rubber and it will crack in short order and the whole job will be wasted. When everything is cured over night spray some silicone on a rag and wipe down all of the rubber to clean it up and protect it. At this point I let it sit overnight and then when everything is set up I install the top molding by starting one end over the channel and then simply pressing it down into place and tapping it from side to side till the screw holes line up.
Installation on the car: Clean the cowl channel and wipe it down well. Trial fit the cowl rubber to make sure holes line up and then use weatherstrip adhesive to glue the rubber strip down in the cowl channel. Install the windshield end post rubber shims at each end in the proper thickness to give even pressure all along the base when it is bolted down. (I used 2 shims on each end) Next make sure all the holes are clear and the t-bolts are correctly positioned in the lower windshield channel and with helper carefully guide the windshield down into place making sure that all of the t-bolts enter and go through the holes in the cowling. Install nuts and washers on all bolts and finger tighten them making sure they are all straight and positioned correctly before starting to tighten down. Iíve heard of many a windshield being broken at this point due to misaligned bolts or un-even tightening. Begin at the center and work towards each end. Incrementally tightening a little at a time. After each round of tightening check windshield base to make sure it is coming down evenly. If something doesnít look right at this point, stop and find out what is wrong prior to commencing with tightening further. I found that sometimes the lower exterior molding becomes partially unseated causing there to be a gap between the molding and the cowl. I found that with a piece of soft wood and a mallet the molding can be tapped down so it properly seats against the cowl again. The nuts that hold the windshield down should just be snugged evenly. You will have to use your judgment here as it is impossible to torque these nuts. They donít have to be real tight but must be pretty snug to get a good seal.
I have not had any problems using this method both times I have done this job. I hope this helps you somewhat. Iím also attaching a few photos showing the sequence of assembly. If you have further questions, feel free to ask away and Iíll do my best to help.
The main thing is take your time, be very patient, let it set overnight prior to putting it on the car
Well, now you know as much or more than I do so there is nothing left to hold you back, so what are you waiting for? Jump right in there and do it.
Good Luck and I hope that in some small way this has been of help to you.