Im making this thread to have a place to put my thoughts and experience on rebuilding my astro tops and why they fail so quickly in the first place.

There is many threads of unhappy customers and if you happen to have a set of defective tops dont bother calling them for help, they will only want to sell you a new pair full price with no appreciation of your previous purchase.

I called hoping they could just reglue the frame to the lens, my lens is in great shape, but I was told my lens was sun damaged even though he did not have any way to look at it. The tops are 9 yrs old but I have not taken a close look at them for ages so these failures have likely been there for some time. The weatherstripping cracks in 3ish years or less, there is even a thread I found where willcox said they do not use the top of the line weatherstripping which can cause window alignment issues as well. Its not easy to tell when the lens starts to separate, you have to get up close and personal to know for sure but slowly over time your car will have more wind noise and water leaks that wont be super obvious because they happen overtime and not all at once. I imagine there are many happy customers who probably store their car indoors and do not have these issues. My car was under a carport under a car cover and driven 10k miles in 10 years and I have had these issues so if you are in similar conditions I would expect similar issues.

I would like to discuss the reasons these issues exists and why their one piece tops have such great reviews. If you look at the c4 forums there are a lot of unhappy customers who have the oem style rebuilt tops. The issue I see with the c3 tops for starters is that astro tops uses paint to black out the area surround the original frames they use and this paint cracks because it doesnt expand at the same rate as the lens. On original glass tops they use a vinyl sticker for the blackout areas. Another issues is that the acrylic lens expand and contracts more that glass does stressing the bond areas more than oem tops. I do not know the primer they use for the areas where glue is applied on astro tops but these areas failed just as much as the painted areas. Another issue I see is that there is zero UV resistant measures on the astro tops. I found primer that is meant for acrylic/plexiglass for boat windshields (sika primer) which seems very high quality but they even mention that you should paint the outside of the windshield where the glue is to be applied so that it can block UV light hitting the primer and deteriorating it. If the astrotops used a clear UV blocking exterior window tint I imagine the bond would last much longer. I also imagine that the reason many OEM corvette tops are reflective/mirrored is that it blocks a ton of UV light and preserves the bond/primers for longer.

So in my astro top rebuild I will be using 3m 1080 matte vinyl for the black out areas on the underside of the lens, likely sika primer but still looking into if there are other options, and I have found a mirrored exterior window tint that I plan to put on the outside of the lens (we'll see how that goes)

To remove the areas of the frame that were still glued, I used fishing line, guitar string and razor blades (only about 1/4 of the frame was still bonded) and in the end I just had to pull the frame off with force, the corner where the handle for the latch is has a lot of glue from astro tops so thatll be a challenging area for whoever tries to rebuild thier own top. Most of the paint flaked off of the black out areas, but what ever was left I carefully used a bent razor blade to remove the paint. This left scratches that I polished out with a harbor freight headlight polishing kit. I havent polished it out perfectly, up close I can still see sanding marks even tho they are glossy, the vinyl wrap will hide these althought on the second top I will try and find a chemical to remove the paint instead but it will be a lot of trial and error to make sure the chemical doesnt damage the lens.

The glue I will use will be some kind of black 3m urethane windshield adhesive and whatever primer they recommend for metal for the t top frame. The glue did not fail on the frame side although the glue used in some areas was thin and could be pulled off so I will make sure to use more than asto tops did in those areas.

The reason the one piece tops do not fall apart is because they are just using acrylic block bonded to the acrylic lens rather than the complicated metal frame and bond. The glue for acrylic to acrylic is extremely strong and basically melts them together making it much less affected by UV light.

The reason they will not reglue your perfectly fine lenses to your frames is because its more work to clean up the lens than replace it with a new one. If you are like me and cannot afford a second pair of astro tops and your lenses are fine, it is possible to rebuild them but be warned its a lot of work.

 

The increased thermal expansion of the astro top lens is likely one of the culprits of the bond failure on these style tops (acrylic lens with metal frame vs the one piece acrylic lens with acrylic blocks for mounting hardware)

Coefficient of thermal expansion of Acrylic (pmma), Glass, and Aluminum.
Acrylic: 68-75 10-6 m/(m K)) Material astro top lens is made of
Glass: 4-9 10-6 m/(m K)) Material orginal lens is made of
Aluminum: 21-24 10-6 m/(m K)) Material of t top frame

Another factor that may effect the lifespan of the bond between frame and lens is the UV characteristics of the lens. Glass blocks some UV rays while pure PMMA can allow more UV light to transmit through effecting the bond. Some PMMA, like plexiglass, can have UV resistance designed into the product negating the concern of UV penetration when compared to the OEM glass lenses. I do not believe astro tops are made with plexiglass.

I would like to add some sort of UV protection to the exterior of the lens but have not yet found a suitable product
The astro top lens may have some UV resistant properties, but I will not be able to confirm without a UV meter

It would be great if it were possible to confirm the products being used by astro tops. I feel confident in the sika products because they are engineered for a very similar application bonding plastic windows in marine applications. The primer and glue are designed to be used with acrylic and looks to be used in a structural way like what will be required for the t tops

A final note is that the thickness of the adhesive astro top used is 1/16-3/32 thick. This relatively thin amount of adhesive likely added to the stress between the acrylic lens and aluminum frame that expand a different rates. Sika products recommends a 3/16 thickness which I will try and maintain with the use of spacers that can be removed after the glue has set and then filled back in. I am not sure that it is possible to have a larger bond thickness but I will attempt to mock it up and see what that looks like on the car.

Links:
coefficient numbers https://www.engineeringtoolbox.com/l...ents-d_95.html
UV statement https://www.hydrosight.com/acrylic-a...raviolet-light
Sika product sheet https://www.chmarine.com/acatalog/295uv-guide.pdf