Rear view mirror attachment to windshield failure - trials and failures

Sorry for the essay – hopefully it will help others too.

Short story – I’m near my end of attempting to reinstall my rear view mirror. After 3 tries, I have a thin ~1.5x1.5 steel plate epoxied to the spot where the metal rear view mirror tab was previously glued. Looking for suggestions. Will share photos later too if it’s helpful.

Longer version: In the past 5 Months I’ve reinstalled my rear view mirror 3 times, and they’ve all failed.

1st try – I was on the road and picked up a Permatex rear view mirror kit at the Autozone immediately after it failed. Note: during this initial failure, the metal tab took a small chunk of glass out of the windshield. I didn’t have any tools to remove the chunk that was still bonded to the metal tab, so I just glued the whole think hoping the glass would fit like a puzzle piece back into the windshield. Other than not removing the glass chunk, I followed the directions in the kit, cleaning both sides while simultaneously applying the glue activator, holding it on the windshield at least a minute. Then I let the glue cure to the windshield overnight (although directions say only 30 minutes curing before reinstalling mirror) and reinstalled the mirror. It broke a few days later – interestingly the glass to glass bond was strong and some (not all) of the original broken chunk stayed glued in the windshield when it failed..

2nd try – After the road trip, back home I ordered another Permatex kit. This time I removed all the glass that was still stuck to the tab. I sanded both the metal tab and the windshield to remove any existing glue. I then thoroughly cleaned with alcohol. I picked a spot with pristine glass about 2 cm below the missing chunk of windshield. This was the best result and it lasted over a month. I walked out to the car one day and the mirror was dangling..

3rd try – I changed things up completely here with a new strategy I was sure would work. I assumed that the metal-glass bond seemed to be the weakest link so I took thin steel plate (the kind that comes with a magnetic phone holder that you attach to your phone. I cut it to shape approximately 1.5x1.5 inches – this is about 5x surface area of the metal(aluminum?) rear view mirror tab. Also this plate would completely cover the missing chunk of glass and allow me to center the mirror in the original location. Maybe the epoxy would also fill in some of this missing chunk and improve windshield integrity if that is even an issue.

I first glued the metal tab to the plate. I thoroughly sanded and cleaned both surfaces. This is a metal to metal bond and I used jbweld clearweld (5 min) epoxy. I clamped and left overnight to cure in the garage at fairly cool temperature (average 65 degrees?). After attaching the tab to the plate, next I needed to attach that entire piece (plate+tab) to the windshield. I read / watched some videos saying this epoxy was a good solution for metal to glass too. I used magnets on both sides of the windshield to hold the entire thing in place and let it cure overnight before removing the magnets. I left town after, so it was another week before even installing the mirror. With a week passed, I put the mirror on, used the torx screw to carefully tighten lightly to the point where the mirror didn’t jiggle. I got in the car the next morning and found the mirror dangling! To my surprise, the metal to metal bond failed – the tab separated from the plate. Given I did this in the garage with plenty of time and space to keep things clean and sand both sides nicely and then securely clamped it, I definitely didn’t expect this. Was setting/curing temperature a factor?

Now: At this point I have a 1.5x1.5 inch steel plate in the middle of the windshield that I can glue the metal tab to. I’m planning to try again.

2 main questions:

1. Should I try epoxy again or a different glue? With epoxy I think the tab is aluminum and not magnetic. Because the steel is already stuck to the windshield, I can’t easily clamp it and it may be hard to hold for 5 minutes for the epoxy to set. I’ve scoured various threads on the internet and primarily see suggestions for Permatex, followed by some suggesting silicon glue, and some for epoxy. Note that the bond I need now is metal-metal.

2. Are there conditions that I can control for to improve on what I’ve already done? The only thing I think I could have improved was doing it at a different time of day? I don’t actually know the best conditions, in terms of temperature and daily cycles to do this. And as a note I live in a mild climate in northern California – temps were reaching a high of ~80 in the day, maybe a low of 55-60 at night (at the time of the last attempt/ failure). The inside car would have been much hotter obviously. But the glue will need to withstand these fluctuations and more in the future anyways, right?

- Lastly, do I need to worry about differences in thermal expansion/contraction between glass, epoxy, steel, aluminum? And with this is mind is epoxy a good glue that can handle this?

Seems like I’m overthinking everything, mostly I’m just frustrated with having a dangling mirror that I can’t seem to fix! Other suggestions?

 

Does your insurance cover a broken windshield?
Check it and see. It might and would end all of your frustrations.

In SC glass damage / replacement is covered at 100% by law. Your state may also have this.

 

Good thinking.. Its been lurking in the back of my mind and this may be the best solution!