Seeing as to how I'm frequently asked about information on self-dimming mirrors, I thought it would be a good idea to start an informative thread outlining how the mirrors work, the different brands and kinds there are, the pros and cons to those different kinds, as well as basic removal and installation instructions. My goal is to make this as thorough as I can, but if you still have some questions I didn't go over, please feel free to ask. I'm not an expert by any means, but I've been fascinated by these mirrors ever since I discovered them 10+ years ago, so I have gathered a decent amount of information about them. Forgive the quality of the pictures. I will update this post when I get a better camera and more ideal lighting.
Quick History & Background
Auto-dimming mirrors are nothing new by any means. The electrochromic technology used to make today's mirrors has been around since the '40s, and has been in use in automotive mirrors since the '80s. The concept of an auto-dimming mirror was first introduced by the Zeeland, Michigan based electro-optical products manufacturer Gentex Corporation. They created the world's first electromechanical mirror in 1982, which found its way into higher end American luxury cars as an option in 1983. It used sensors to detect glare from behind. The sensors were connected to a small motor that would move the angle of the mirror to adjust accordingly. In other words, it basically acted as an automatic version of the flip tab on standard mirrors. These mirrors would be available through '91.
In the meantime, a father and son team of chemists convinced Gentex that they knew how to apply electrochromic technology (a gel that darkens when electrically charged/clears with no charge) to their mirrors. After investing a lot of money for R&D, they found a way to sandwich a thin layer of the gel between 2 pieces of glass, and have it react to an electrical charge initiated by sensors mounted on the front and rear of the mirror when they detected glare. The first electrochromic self-dimming mirror was introduced in '87, and was made available in the '88 Lincoln Continental, and 8 GM cars in '89. They became more commonplace in the early '90s.
It is at this point that Holland, Michigan based Donnelly Corporation, another major automotive mirror manufacturer, came into play. Gentex' auto-dimming mirrors were a huge success, gaining more and more car manufacturer contracts. Donnelly was trying desperately to take back some of the market share by producing mirrors with very similar technology. In may of '90, Gentex sued Donnelly over patent violations. Through a mess of suits and counter suits over the next few years, as well as out of court settlements, things finally cooled down between the companies. In the meantime, Gentex continued to expand upon what they started with their mirrors. In '93, they introduced the first self-dimming mirrors with a compass that showed the direction you were headed in a little digital display within the mirror itself. These mirrors would become available on '94 model year luxury cars. From '97 - '98, cars would start receiving self dimming outside mirrors, inside mirrors that displayed compass as well as outside temperature, and compass mirrors with LED map lights, which were ONLY available as an option on the Intrigue GLS in '98. The GLS also had this same mirror available in an OnStar equipped version.
Fast forwarding to today, Gentex has grown immensely, and is regarded as the leading company in auto-dimming mirrors with distribution in several countries, including Germany and Japan. They have expanded their contracts to almost all car manufacturers around the world, and self-dimming mirrors are no longer something reserved for higher end luxury cars. They can be found in all sorts of makes and models in many variations. The features have also increased dramatically, including versions with HomeLink, back-up camera and navigation. Meanwhile, Donnelly lost a lot of ground in the war for market share since 2000, and is virtually non-existent in the manufacturer's contract department.
Gentex vs. Donnelly Pros & Cons
Being the 2 major producers of auto-dimming mirrors, these two have been dueling each other for a couple decades now. Virtually every feature Gentex came out with, Donnelly would copy. However, the 2 companies took a very different approach as far as aesthetics. Donnellys had more of an "egg shape" to them, especially if they had temp and compass, because they put the display for those in the base of the mirror as opposed to in the mirrors themselves like Gentex does. The front of a Gentex mirror looks more like traditional mirrors, but with a bit of an extension at the middle of the bottom for the buttons. Personally, I prefer the way Gentex' look a lot more, but that's subjective. One plus for Donnelly mirrors is that they are much more commonly available with map lights. Since most of the vehicles that Gentex' originated in were luxury, or well equipped, they usually already had some kind of fancy overhead console or dome light, so they scarcely received map lights in the mirrors.
Fully optioned Donnelly mirror.
However, this and all other advantages for Donnelly mirrors are a moot point because of one monumental problem they're prone to which renders them useless. Donnellys are notorious for breaking and leaking the liquid inside of them, often causing discoloration in the paint when the liquid eventually drips onto the center console. Why is not completely known. However, I mentioned the legal troubles between the 2 companies earlier, and that Donnelly had to change their methods of accomplishing the auto-dimming effect due to patent infringements. My theory is that whatever they did to change the process for auto-dimming, it was an inferior process with poor reliability/durability. On the other hand, I've never really heard of a Gentex mirror failing in any capacity (certainly not by leaking out the gel). It is for this reason that I usually suggest people switch to a Gentex when their Donnelly mirrors finally fail, which they inevitably will.
Mmkay, now for the good stuff you've been waiting for.
Removing and installing auto-dimming mirrors
Removing factory auto-dimming mirrors from the windshield
*DISCLAIMER: The process for removing mirrors with the newer mounting style can put your windshield at risk for cracking or breaking. I am not responsible for any damage. Attempt at your own risk!
This will actually be the hardest part of adding/replacing an auto-dimming mirror. Rather than using the traditional, easy-to-remove single torx screw to tighten the mirror onto the windshield button, newer auto-dimming mirrors have a tensioned spring with tabs in the brackets that, once the tabs clear the windshield button, locks it into place, making removal a serious pain by comparison. To get an idea of what you’re dealing with, here is a mirror off the car with the spring/tabs exposed (tabs circled in blue). It is this spring that has to be pushed in towards the mirror so that the tabs on the spring will clear the mounting button, allowing the bracket to slide up and over it.
You will basically have to insert a small slotted screwdriver into the slot opening at the bottom of the mirror bracket’s base, and gently tap at the screwdriver (preferably with a rubber mallet) till it pushes the tab back far enough to clear the button. The screwdriver is in far enough when it won’t fall back out with little force, but at the same time, not so snug that it takes a lot of force to get it unstuck. Take your time, and check to see if it’s at this point with every few taps. Driving the screwdriver in too far can cause the windshield to crack or break. Here’s an off the car visual to give you an idea of what you’re looking for.
At this point, the mirror bracket should slide out by gently lifting UP on the mirror while wiggling it back and forth.
Again, I have to stress to be extremely careful with the removal of these mirrors. The process itself sounds straightforward and easy enough, but the springs are often stubborn, so you have to be very cautious not to exert enough force to break the windshield.
Tip: If you do not feel comfortable trying to remove the mirror yourself, skip to the wiring so that’s in place, and then take the vehicle to a glass or body shop to pop the mirror off. Most will remove rear view mirrors for $10 - $15, and many will even do it for free! Same with reattaching mirrors that have fallen off!