Came out to the truck the other day and the mirror was on the floor. This happens too often for me. The last one was a few months ago. I do everything it says on the package and more with the cleaning. My truck is parked facing the east out in the open and the Florida sun has been really strong. My wife had to drive 500 miles yesterday with only the outside mirrors but she's a trouper. I'm thinking about putting a piece of duct tape outside on the windshield. Any other suggestions?

]

 

On my 94 Taurus I noticed that the bond had failed at the Glass surface. SO, I made sure All of the old adhesive was removed from the windshield glass & metal mount. I put on rubber gloves so oil from my fingers wouldn't contaminate the glass & metal bond areas. I wiped the glove fingers with a clean non linty wipe wet with the isopropanol to remove any glove mold release that might be on them.

I rough cleaned the windshield bond area (that I outlined on the Outside with a magic marker, for later mirror mount alignment reference) with a new single edge razor blade to make sure all old surface adhesive was removed. Cleaned the glass bond area with a fresh lint free wipe dampened with 70% isopropanol, Then Final cleaned the windshield glass bond area with another lint free wipe dampened with ammonia bi-fluoride, the metal mount bond area with a clean lint free wipe dampened with 70% isopropanol that you can get at Wally-World..

Before final cleaning the metal mount with the propanol, I Figure 8 rough sanded the metal mount bond area with 240 grit Wet carbide sand paper on a Flat surface. All to make sure the bond area was Flat & was down to All Bare metal, so to get more metal bond Surface Area with the course 240 grit figure 8 swirl marks. Then Final cleaned the mount bond area with a propanol dampened Clean wipe.
Gotta Get & Keep Both mounting surfaces & the gloves squeaky clean & lint free & Not touch the mounting metal or glass with our Bare fingers, dirty wipe, or dirty gloves, or lay the cleaned mount bond area on a dirty, or linty surface that'll re-contaminate the bond area.

I precut tape strips & had them ready to hold the mirror mount in place with my outside magic marker outline & so to hold the metal mirror mount Still, over night, before hanging the mirror on it. So to give the adhesive its Full cure time before re-hanging the mirror & over stressing the bond line before its had time to Fully cure & attain its full bond strength. So use the tape to hold the metal mount in place so it isn't being moved around while curing, or hanging the mirror on it before it Fully cures, as those things can mess with the product strength & its surface bond strength.

Yah I know all this detail sounds super ****, but we want a long lasting bond, thats going to see Severe service, last a looooong time, so to build on your shading idea, you might consider painting, or bonding a metal shield on the outside of the windshield to help shade the inside bond area from the outline, so to shield from the sun UV & IR heat. Auto glass is a good short wavelength UV attenuator, but the longer wavelength UV might be making its way through strong enough to affect the bond over time. Or maybe you need to install some vent shades & lower the side windows some, so to lower the cabin heat & help keep the bond area cooler, in case the product your using has a heat tolerance problem.

Make sure to use a Fresh, name brand adhesive kit, don't buy off brand & don't reuse any left overs from previous kits. I used a Loctite kit. They make their own adhesive & primer, so have good control over the process But we have to make sure we're getting Fresh product from the store because Loctite can't control how their customer stores or displays the product.

I digress, My old Advance Auto used to have their adhesives on a West facing shelf on a Glass Wall. Everything on that shelf that wasn't new had seriously Faded packaging & Cooked goods inside. I finally convinced the store Manager to move the adhesives to the back of the store & put his shinny chrome items on that window shelf, as the sun won't hurt chrome but it'll sure get guys driving by attention & likely increase customer traffic!!!! It worked. lol He got more customer foot traffic & I got fresh adhesives, so we both won on that move!!!

Anyway, thats the **** detail on what I did to fix my 94 Taurus inside rear view mirror falling off woe, about 20 years ago & yup, its still on there as of yesterday, so give the details a try & let us know how it goes.

 

I prepped and cleaned like you said but didn't sand the metal hanger; sounds like a good idea, I'll do that when I get the adhesive and either put a piece of tape or paint with a light color on the outside of the glass.

 

I forgot to specifically ask Which Surface still had the adhesive attached, the windshield glass, or the metal mirror mount surface???? The surface Without any adhesive, is the problem bond area. So needs a .different preparation approach.
The 70% propanol will degrease really good & the ammonia bi-fluoride will super clean & micro etch the glass surface, giving its bond line a good grip with more surface area, like the figure 8 swirl marks on the metal mirror mount does for its bond line.

On applying the curing agent, I applied it to Both surfaces, the glass magic marker outline & the metal mirror mount & let it fully dry as the instructions say.

On applying the adhesive, put it in a line centered on the metal mirror mount flat surface & touch that centered puddle line of adhesive to the Center of the mount magic marker outline & slowly press the metal mount so the adhesive will evenly spread from the center outward, evenly pushing the air away as the adhesive spreads to the edge of the mount. Then apply your tape to keep the metal mount from floating / moving around & moving off center, until it Fully cures. The parts need to be still, not moved around while it Fully cures, so to get the strongest bond & strongest cured material. Applying the adhesive to the center line of the mount will help prevent trapping air bubbles in the glue line & that'll make it stronger.
Will be interesting to hear how it goes & holds up over time.

 

I just walked outside and looked @ the adhesive on the glass and the metal puck. It looks like it's about !/2 on each. The metal has adhesive in the middle and the glass is mostly around the edges. Another thing is the truck was probably 150* when I opened the door. There's no way to have a window open because we have thunderstorms almost every afternoon here in N GA. I'm getting a ordered from Amazon, next week so I'll try it again. I really think the sun beating down on the windshield is heating it up beyond it's sticking range. I don't remember it falling off during the winter but I'm an old man and might be mistaken.

 

Ok, thats good feedback, so lets think about this some more. Since there is about 50% adhesive material remaining on Both halves, I agree it sorta suggests a material problem. Since this material likes to cure Completely, Without Movement, before loading the mount with the mirror weight, all of which can disturb its cured molecular structure, try to remember How & for How long, you've been securing the mirror mount to prevent movement & how long have you been allowing it to cure Before re-mounting the mirror for use???

 

I don't remember the last time but next time I'll leave it overnight or maybe, if I don't need the truck, several days.