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Acrylic Roof Bonding

Hot Rod Roy

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Joined
Jul 6, 2005
Messages
317
Location
Mission Viejo CA
Corvette
Yellow '84 Coupe
I know there are companies that rebuild acrylic roofs by replacing the roof panel on your frame. My acrylic panel is in good shape, but it has come un-bonded from the aluminum frame on my '84. I can't be the only person to have this problem, but so far, my attempts to re-bond my roof panel to the frame have only lasted for a short time. Who's got the answer here? There's got to be a better adhesive that will stick to the acrylic that I haven't been able to find! I've even adjusted the hold-down brackets to reduce the stress on the bond area, but am still having problems.
 

ecss

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Joined
Nov 27, 2004
Messages
649
Location
Windsor Mill, MD
Corvette
89 Brilliant Red Metallic
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Hot Rod Roy

Well-known member
Joined
Jul 6, 2005
Messages
317
Location
Mission Viejo CA
Corvette
Yellow '84 Coupe
Thanks, ecss. This is some good stuff! Is this what Corvette used to put these cars together? Sounds like you've got an inside track to the adhesives engineering field. The guarantee is for metal to metal, in un-stressed applications, so it's not quite bullet proof. I think I discovered the stress limits of my roof when I hit a big bump going around a fast corner and went airborne! Exciting? Yes, but I wouldn't recomend it. '84's are well known for liking fast corners, but that was just too much! I'll check out this super adhesive. Thanks again! (I'm sure glad my wife wasn't with me!!)

:thumb
 

ecss

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Messages
649
Location
Windsor Mill, MD
Corvette
89 Brilliant Red Metallic
You hear more complaints about the factory acrylic tops crazing and developing what appear to be stress cracks more than the top separating from the frame.

At one time Melrose sold a replacement acrylic top by itself. You could try contacting them and see if they they recommend a particular adhesive. They claim to be licensed by GM to repair the tops. :upthumbs. I have a feeling it may be top secret information. :chuckle Stay away from Astro Tops if you purchase a replacement top.

Here's a link to Melrose. I've read about some of their
replacement tops separating and the acrylic cracking so using acrylic for the top wasn't a good idea considering how much the C4 flexes.

C4 Corvette Roof Replacement
 
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Hot Rod Roy

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Jul 6, 2005
Messages
317
Location
Mission Viejo CA
Corvette
Yellow '84 Coupe
I don't think we should bad mouth the Corvette engineers for the acrylic top. They designed a beautiful car, and mine is coming up on its 30th birthday! Since we don't hear of many de-bonded tops, they did something right. My "stress test" was certainly outside of the design specifications for the car. The adhesive they used had to withstand the high temps of an Arizona heat wave, the cold of Connecticut, and all with crazy, vigorous drivers trying to lift a front wheel in the corners! And now, 30 years later, I'm having trouble finding something as good as the stuff they used! I still marvel at the talent of those engineers as I work on my car! Thanks, guys, for a (mostly) good job! What a huge improvement over the C3.

:D
 

Hot Rod Roy

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Jul 6, 2005
Messages
317
Location
Mission Viejo CA
Corvette
Yellow '84 Coupe
After reading the detailed information about the Lord Fusor 116 adhesive, I decided that's not the right stuff. It's designed as a hard bonding agent that can be ground and filled with body fillers for painting. The thermal coefficient of expansion (c.e.) of acrylic is about 4.5x10(-5)/*f, and the c.e. of aluminum is about 1.3x10(-5)/*f. A hard bonding agent will crack with temperature extremes, and my dark top does get hot! I found a urethane adhesive, Dow Chemical Betaseal U-418, which looks identical to the soft butyl-like adhesive Corvette originally used on the roof. I'm giving it a try. Hopefully, it will let me drive more than 20 mph without the roof flying off. From now on, all four wheel stay on the ground! ( www.dowautomotiveaftermarket.com )

:pat
 

Schrade

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1,315
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Not in CF; BANNED!!!
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'90 LT 5
Have you thought of trying to lay a bead of RTV / Silicone in the channel? The hard bonding agent that you referred to probably IS not the best stuff; RTV dries like latex and bonds as good as anything I can think of...

If I ever get my car back, and get TO the top, I'm gonna' give it a try. Only thing I can't grasp fully is removing the acrylic top from the top frame.
 
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Hot Rod Roy

Well-known member
Joined
Jul 6, 2005
Messages
317
Location
Mission Viejo CA
Corvette
Yellow '84 Coupe
Yes, I tried a "high strength" RTV intended for bonding. Some RTV's specify they're for sealing, rather than bonding, and those are low strength. That RTV lasted for about three months, then started coming apart. My first clue was the sound of an air leak at the top of my windshield.
It's not as hard to separate the acrylic top from the frame as I expected it to be. A narrow putty knife, wiggled into the adhesive from the inside of the frame, will cut the adhesive. There are four pads, one in each corner, which contact the acrylic panel to provide the proper spacing between the frame and the roof panel for the factory assembly tooling. Try to avoid damaging these four pads, which look like a nylon material, and are about 3/4" dia.
The Dow adhesive appears to be a much better adhesive than anything else I've tried. It's some really sticky stuff. Very messy to work with. So far so good!

:thumb
 

2VettesMike

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Joined
Sep 27, 2006
Messages
131
Location
Blk Mtn, NC
Corvette
1972 Bryar Blue Coupe 1993 40th Coupe
You hear more complaints about the factory acrylic tops crazing and developing what appear to be stress cracks more than the top separating from the frame.

At one time Melrose sold a replacement acrylic top by itself. You could try contacting them and see if they they recommend a particular adhesive. They claim to be licensed by GM to repair the tops. :upthumbs. I have a feeling it may be top secret information. :chuckle Stay away from Astro Tops if you purchase a replacement top.

Here's a link to Melrose. I've read about some of their
replacement tops separating and the acrylic cracking so using acrylic for the top wasn't a good idea considering how much the C4 flexes.

C4 Corvette Roof Replacement

X2 on Astro Tops. The top they used is a lot thicker, doesn't fit the clips in the hatch area and are prone to leak in the front corners. If I had only not traded in my old top.....

Mike
 

gmjunkie

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Nov 11, 2004
Messages
4,547
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
Only thing I can't grasp fully is removing the acrylic top from the top frame.
You can cut it off with out damage with a Guitar B or E string!:thumb
What your going to find is corrosion on aluminum frame between the Frame and Urethane Adhesive!:thumb

Been There,Done That!~!! ........at least a hundred times.

:D




For lexan tops I use "ONLY" 3M Windo-Weld Super Fast - PN 08609 :thumb
It's a fast set Automotive Urethane for setting Windshields and Fixed Windows,When cured it remains strong,flexible and will "NOT" compromise the structural integrity of the vehicle!:thumb:thumb
Sets in about an hour and will be completely cured in about 24.:thumb:thumb:thumb

:beer
4143.gif
 
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