A Perfect Convex Glass Replacement for our Cowl Mirrors

[patrickt]

Replacing the tiny rear view mirror that sits on the cowls of our Cobra with a high quality OEM night-sensitive convex mirror is not nearly as difficult as you might imagine. First, you have to find just the right mirror. It has to be optical grade first surface reflective and ground to allow just the right amount of light to pass through the mirror itself (which helps with night driving) and it can't be too convex or not convex enough. Then all you have to do is disassemble your old rear view mirror, cut the new glass mirror to just the right size, then reassemble it all without breaking it. Piece of cake.

Over the last few months I've bought half a dozen or so different mirrors, all with different curvature of radius values (which is how "convex" it is) and different optical quality. I ordered some nice 3000mm radius curvature glass from Japan, but that wasn't convex enough and the Longacre Racing Mirror glass was a little too convex for my liking (but not terribly so and you might find you like it). Finally, I found the OEM General Motors replacement glass for the lower outside passenger towing mirror on the C/K Pickup that you got with the towing package. Beautiful first surface mirror, just the right curvature radius, and it is optically tuned to allow light to pass through it. Plus it doesn't have that pesky "Objects in the mirror..." message since it was for towing and skirts those regs. Just the quality of the image compared to the cheapo mirror that comes with our cowl mirrors was astonishing. Now to cut it...

At first I tried a traditional glass cutter where you score the mirror, run the score and then snap it apart. That resulted in me buying more mirrors. Don't even try a glass cutter unless you have some sort of super human skills. Instead, go straight to the Dremel Diamond Cutting Wheel #545 and punch a pin hole in a plastic water bottle so that it "pisses" a stream of water out the hole. Do not use the diamond wheel dry. Aim that stream of water right at your glass as you cut it with the wheel. Voila!

Figuring out how to take a picture of the original mirror, and the new mirror, so you could see the difference was not easy. Here's a pic that gives you the orientation of looking at it while in the car and a fence as the image. The second pic is just to show you how clean the cut is (that mirror is the first one that broke when I tried to use a glass cutter on it).

Here's the new mirror assembled in the original frame, which could stand a little touch up with flat black paint.

[jeffgrice]

Nice work

Here's the clip on mirror I have used on several Cobras: https://www.amazon.com/EPARTS-Univer...23711245&psc=1

Jeff

[patrickt]

Originally Posted by jeffgrice

Nice work

Here's the clip on mirror I have used on several Cobras: https://www.amazon.com/EPARTS-Univer...23711245&psc=1

Jeff

Yes, I've seen that and it's pretty nice. It's a shame they insist on splashing their logo on it. I'm not sure whether I like the blue tint or not. It might clash with beige. One of the problems with remedying the mirror problem on our Cobras with convex mirrors is that nobody, with the exception of Talbot and some Japanese places, tell you what the radius of curvature is. If you call them up and ask them what the radius is it's like asking them to explain the unified field theory to you. When I replaced my driver's side Talbot knock-off with the true Talbot mirror glass they were kind enough to send me the specs on it. The radius of curvature for that mirror was 40 inches. A beautiful piece. First surface reflective, optically translucent, really nice. Here's that old thread: A Replacement Convex Mirror that Really Works The radius of curvature for my rear view mirror in this thread is slightly greater, thus less convex. Clearly easy to see by putting the mirrors next to one another and looking at your face. U.S. regs prohibit driver side convex mirrors, mandate that pesky message on the passenger side, and limit the radius to be between 40 and 60 inches for that side. No convex interior rear-view mirrors or driver side allowed, regardless of the fact that there is ample data that it reduces blind spot accidents. Europe uses them, as well as aspherical mirrors, which I have no personal experience with. Accessory mirrors for towing, and race mirrors, apparently fall outside the regulations. And I don't know what the rules are for tinting but the specs for translucency and reflectance are pretty specific. But the stock Cobra cowl mirrors that almost all of us use are really no better than your wife's compact mirror that she keeps in her purse. And the optical quality isn't even as good as your bathroom mirror.

[Morris]

Here’s one that we use on the track....

[patrickt]

Dang, that looks like you could almost pop that on over the stock ball stem that we use for the standard POS mirror.

[Blas]

If you run over to your local auto parts store and purchase a good quality glass clip-on mirror or a replacement glass blank, you can remove the glass and disassemble your current mirror and take the SS plate (or a facsimile of it) to a local stained glass window shop and you can have them cut a blank and use a wet grinder to match the shape exactly. You must remember to modify (bend) the mirrors edge channel to match the curvature of the new glass and not over tighten the mounting clip. I also recommend also a coat of silver paint on the edge of the new glass to keep moisture from attacking the aluminizing on tge glass.
Blas

[patrickt]

My fall back plan, if I just couldn't cut it myself, was to go to a small family owned glass shop and see if they would do just what you suggested, but the Dremel Wet Diamond Wheel cutting technique really was easy. Now, the difference between a first surface reflective mirror, which uses chromium, and the lesser quality mirrors, which do use aluminum or zinc really is astounding. Even in my crappy picture comparing the two the brightness and clarity difference comes out.

[bwcobra15]

Patrick, do you happen to have the GM part number of the replacement glass you used?

and... how did you remove the original mirror glass and replace with your cut piece?

[patrickt]

When you remove the screw that holds the clamps around the top and bottom of the mirror, as well holding the clamp to the end of the ball on the stalk that is screwed in to your cowl, the clips can be removed from the mirror assembly that surrounds the glass and you will see that it is a frame that can be gently spread apart. It is much easier than you think. Here is the link to WLLW, which is an automotive mirror supply store that sells off of Amazon. I was quite pleased with the quality of their wares as well as their service (and I bought more than one mirror from them). You might find that you need to replace the backing plate behind the original mirror with something a little thinner (since the new glass is slightly curved). A piece of slightly thicker, but not too thick, plastic works like a charm (I used a piece of plastic separator that I found in one of the kids school notebooks from decades ago -- just trimmed it with scissors). Then paint the inside of the plastic with a flat black paint to absorb light passing through the mirror and the outside, which would face the the front of the car, with a wrinkle finish black paint so it kind of looks like it did 50 years ago, dust the frame with a flat black, and you're done.

https://www.amazon.com/dp/B07H7ZFX5M...t_details&th=1

[patrickt]

This is what I have on my shelf for making wrinkle black finishes. Follow the instructions and it works surprisingly well. Bought off Amazon.