The Nut Behind the Wheel: Summer 1999

In the last issue of Moss Motoring, I introduced the topic of windscreen glass replacement and shared some of my secrets in re-glazing the windscreen frame. This time, let’s continue with the attachment of the completed frame to your car and the replacement of the windscreen to scuttle seal.

The four-cylinder’s folding windscreen frame chrome side pieces attach to the pillar pieces with slotted, cone head shaped machine screws, and must be assembled together before replacing the glass. The frame is recessed slightly to receive these screws, and they are truly special, as their heads are quite shallow. All of this is to prevent the screw head from contacting the edge of the glass. Contact will lead to cracking, for sure! If you can’t salvage yours, it’s best to order the right stuff. Normal hardware substitutes stand too proud of the frame and quite possibly will lead to a cracked windscreen. As for the tapped holes in the aluminum pillar posts, they must be cleanly threaded to their complete depth so that the screw can bury itself all the way. If any of these are broken, they must be removed any which way you can, the hole re-tapped, or, in extreme cases, relocated. The windscreen frame must exactly match the contour of the pillar and all the holes must line up. If they don’t, the screw head risks standing too proud of the frame. And guess what? Yep! More possibility for a crack!

On the roadsters, the glazing rubber and the windscreen form a sandwich that must easily fit into the channel in the frame. On the late model sport convertible cars, a one (or two) piece molded glazing rubber is used instead of individual strips. For all models, however, if the glazing rubber doesn’t fit easily and smoothly, then go back and make sure the frame is the right contour and that the frame’s channels are open enough to receive this sandwich. They should be tight enough that you can just push on each frame with a little effort without distorting the glazing rubber.

If the pressure you are applying to get the windscreen and seal to enter the frame channel is cutting the glazing rubber, the channel is too tight. One additional tip is to tape the glazing rubber to the glass to prevent it moving around on you. Be sure to relieve the corners somewhat on the roadsters by cutting and joining the strips at each corner on a 45 degree angle. The trick is to form that perfect joint after the frame is assembled and the corners pulled in tightly. The sport convertible’s glazing rubber corners are already molded to fit.

To aid assembly, it helps to have something that will allow the rubber to slide into the channel. I’ve used or heard of being used motor oil, window cleaner, mechanics hand cleaner, liquid soap, bar soap, and so on. All of these cause some problems of holding the glazing and windscreen in alignment while feeding the frame over them. It seems to always take more hands than I’ve got. My favorite slick stuff is liquid window cleaner. Less messy!

After assembly, and after you are happy with the fit of everything, then and only then, on the roadsters only, cut off the excess window glazing flush with the chrome edge of the windscreen frame. I use a sharp X-Acto knife. A razor blade will work, too. But be careful to cut only the rubber. Don’t press so hard you etch the glass. A scratch can lead lo a crack!

How to get that bottom seal into that T channel? I use a large blade screwdriver that is not sharp, but is rounded somewhat. I hook one side of the T into the channel and ease the other side in, a screwdriver blade’s worth at a time. Yes, it takes patience, and some time, to do this. But this is the only reliable way I’ve been able to do it. I’ve never had one just zip into place, no matter what technique I used. If this is your first try at this, then practice with the old seal. If you are careful, you won’t mar the chrome, as all the pressure is on the rubber. If you are cutting the rubber, then you aren’t doing it right—the channel is too small, or your screwdriver is too sharp. Fix the problem and press on. And don’t put any slick stuff in the channel. You want that T to stay in there! Some of these replacement seals are quite stiff and will spring right out before you can get it all in. At least that’s my experience. Wonderful!

In trimming the bottom seal to the car, make sure that where you cut is where it really seals the pillar post to the windscreen and the scuttle. If it’s not right on, when you drive your car in the rain, you will get water into the car from under this seal. I wait and cut this seal on the car as part of the attachment process to make sure it’s cut in the right place.

Now that the windscreen and all the pillar post hardware are assembled, it’s time to put the assembly on the car. Here, it is especially important that the windscreen assembly fit the scuttle just exactly. For all three types of windscreens, the parts lists call for “packing” pieces, basically just strips of aluminum, shim-like stock, that are used to take up minor differences in the bodies and make sure there is no tension introduced to the windscreen assembly. If you draw in the bottom of the pillar posts, it will begin to pull the top apart, leading to separating of the components on top, and compression of those on the bottom. If one side is too far forward, you risk twisting the assembly. Twisting and separating can lead to cracking. The objective is to place no strain in any direction on the windscreen when attached to the car. On the late model cars, the vein window frames can be used as an alignment guide provided they, too, haven’t been removed for restoration. On the earlier cars, side curtains can be used to some extent if they fit the old windscreen. But be careful if you have never used them, as they are adjustable, may have come loose, or never fit properly in the first place, and so aren’t worth a darn as a guide. More importantly, the hood (as in convertible top) can also be used to check for alignment and that the windscreen does, indeed, fit!

A last thought. If your hood has shrunk with age, it may not fit the windscreen in any case. I’ve known several owners who hadn’t had their tops up in years, had replaced a windscreen, and in cold weather did manage to get the top to clamp closed, only to come out the next morning and find a cracked windscreen. Too much tension! Don’t let your passenger use the top of your roadster windscreen as a grab handle. I have them use the grab handle on the dash. That’s why it’s there! I hope this helps you to get this important component installed correctly the first time, whether you have a glass shop do it or you do it yourself. It’s not real fun experiencing the dreaded “crack of doom” after spending many hours reglazing your windscreen.