BBRYANT

I recently had the top of my 05 C6 blow off the car at 80 MPH. As a new Forum member, I want to say thanks for all the support I received in your comments. GM provided a new top, incliding new paint under warranty, as they should have.
Naturally, I do not ever want the experience again. Therefore, I started looking at how this egregious failure happened. The answer to the top delamination issue is basically bad design driven by, cost management and weight management. Here are the points.
1) Air flow over the top remains laminar to a point just behind the leading edge of the top skin. A low pressure area (disturbed, non-laminar air flow) develops about 3 inches behind the leading edge of the top and extends rearward to the rear top latch, where the dynamic air flow over powers the low pressure and then directs the air over the rear glass.
2) As speed increases, the low pressure area over the top intensifies. As the low pressure intensifies, the top skin is pulled upward and the top skin deforms. Corvette/GM added a structural trough in the center of the top skin to resist the deformation, but it is not strong enough.
3) With the top deformed, the only area that can move is the leading edge, center of the top skin, as this center leading edge area is the "least" attached and weakest part of the top. The right and left leading edge is held in place by the wind screen latches. The top cannot move rearward because of the two fixed pins in the targa post and the rear center latch.
4) Since we are talking about a Corvette, not even GM is going to be surprised when one of their creations is driven fast. In the case of the C6, it is capable of speeds in excess of 180 MPH. Now, get your little speed machine up to 145 or higher and the low pressure area over the top is "intense". Get it up to 180 and the pressure will likely be approaching the catasprophic failure point. At high speeds, the chemical/thermal adhesive bond between the top frame and the top skin will be highly stressed. If high speeds are experienced often enough, the adhesive bond will fail and it will fail nearly every time at the leading edge center of the top skin. Once the adhesive bond is broken, the laminar air flow will enter the vehicle between the top skin and the top frame. You will hear the air leak and if water is present, it will also come inside the car.
5) Why is this top a bad design?
a) The rear of the top is installed first. If we drove around in reverse, it would be a good design.
b) The leading edge of the top, after deformation is exposed to laminar air flow. The only thing keeping the air out is a 3/4 inch adhesive stripe.
c) With the leading edge, by design, going into place last, when failure occurs, the top has only one way off the car, over the rear glass.

What will fix the problem? Answer- Redesign the top! Some suggestions;
1) The leading edge of the top should attach first, followed by the rear.
2) Change the windshield top finished edge design and incorporate an overlap, a grove if you will, into which the leading edge of the top skin fits snugly under. Get fancy and mill or mold a slot tongue on the leading top skin edge and the lap joint will disappear as the top skin meets the windshield fascia. What is accomplished is the formation of a mechanical bond between the top skin and the windshield frame. Secondly, when the top deforms at high speed, the leading edge is protected from laminar air flow. (Think fighter plane canopy)
3) Add a stiff rib to the under side of the roof panel on each side of the structural trough. This would add a small amount of weight. If you simply mold the ribs when you have the top skin made, the cost should be small. Yes, you would have a two piece headliner, if you lack imagination.
4) Replace the two fixed pins with latches built into the targa post and leave the rear center latch as is.

In conclusion, this seems like a no-brainer to accomplish, but I do not have green shades and layers of Corporate nay-sayers breathing down my neck. However, if GM took this advise, the top delamination issue would stop costing them money. If the new Z06 has a similar risk exposure, god help the driver going north of 200 MPH when the top skin departs.

Happy driving my Corvette,

Bill B

vetteman22

I thought the problem was caused on early cars that had defective glue or wasn't applied properly? Did you have one of the early cars or are all of our cars subject to this happening?

rmp

and the NHSTA.

tom4416

How did you measure pressure at speed or do you have access to a wind tunnel? I ask because what you are stating is not what was shown in the early wind tunnels tests before the car was on the market. One of the car mags had pictures two years ago in the tunnel with smoke passing over the car (granted, it was a static photo) and it didn't look like there were pressure pockets such as you described but I don't remember what the tunnel speed was (or if it was even mentioned) so maybe it was 40MPH and means nothing.

I think GM just went to the low bidder for the tops and they are using an adhesive that is thermal sensitive. The majority of people reporting the problem have mentioned they own a black car which obviously builds up and retains heat greater than the other colors.

We glue airplanes together today, must be adhesives that can withstand airflow and temperature extremes! Probably cost fifty cents more per application so it isn't being used.

C6 Strangebob

I can't believe the folks whose tops separated were all doing 145+. I've done 125 and had the car out in the sun for several days at a time, and there's no hint of separation. Mine was built at the end of August; possible the problems were resolved by then. JMHO

Shrike6

Also BBRYANT had his top blow off at 80 mph. Other delaminations took place at lower speeds, and most didn't completely blow off. I suspect poor adhesive bonding due to poor technique (failure to use enough adhesive), or inadequate adhesive properties. Or both.
Bonding of dissimilar materials (magnesium frame and composite panel) is tricky. If the frame were made of composite, no problem. Dissimilar materials expand and contract at different rates ( coefficient of thermal expansion). This is supported by the black car/ hot weather experiance.
The Corvette spent lots of time in the wind tunnel, and the likelihood of such a marked low pressure zone is unlikely. Any delaminations at the Nurburgring? Or at the American lemans series? Naw, poor manufacture process/ inadequate adhesive properties.
That said, I like the idea of the leading edge lip fitting under agroove in the windshield frame.
Didn't someone's delaminated top have no evidence of adhesive, only double sided tape?
It will be interesting to follow this problem as it gets nailed down.
GM

ilkhan

Just a reminder of the "official word", which was that a batch of tops from the supplier was finished incorrectly or had a bad batch of glue or something. I seem to recall the tops in question being may-june-early july timeframe.

GTC

That's what I thought by what I've read in these types of threads.

The roof panel is attached to the frame by double sided tape and glue.
The double sided tape is used to hold the two parts in place as the glue is drying.
There was a manufacturing quality problem where they shipped roof panels that never received the glue, but by external appearances they looked ok because the double sided tape held it together.
After enough time on the road, the double sided tape is not going to hold, and *whoosh*, there she blows.

I haven't had this happen to me, so this is only second-hand info. Is this an accurate summary of the problem?

mikeyc6

I thought this case was one where the top got damaged and then repaired by a non-GM "authorized" shop and the repair didn't hold. Isn't this a simple case of a botched fix?

Mike

Shrike6

That's the 411 so far.
GM

Jeffthunbird

Anybody got pics of a damaged roof?

CV62

I had the same happen to my top and posted a thread with pictures back in August.
http://forums.corvetteforum.com/show....php?t=1165798

My original looked like it had no glue. The dealer first tried to fix and used windshield epoxy. They let it cure for 96 hours. 15 minutes after I picked it up, it started to delaminate again. The surface appeared to be impervous to any adhesive and peeled of like elmers glue.

My dealer finally replaced it with a new one from GM. It arrived basic black and had to be repainted VicRed. All hardware including latches and liner had to be reinstalled. They tried removing the old liner which looked like crapped so I insisted on a new one. Once recieved they assembled everything and I have had no problems since.

If you have an earlier version, beware as it will happen to you so listen to your vette and if you hear wind noise or creaking, take notice.

vetracer

The Z06 uses a totally different fixed roof panel.

PoundF15

I'm not sure where your info came from...it sounds close to me...

But I'm fairly certain the laminar air flow over the top is decreasing the pressure (Bernoulli's Principle) causing lift on the roof, which in turn causes the deforming you talk about and separation and putting the metal skin into the airstream which results in the failure.

The disturbed air you talk about would actually decrease the low pressure area above the roof...think stalling an airplane wing. That would help keep the roof on there.

I agree with making a permanent attachment on the front to prevent the leading edge being pulled into the airstream. And there should be some kind of bracing to prevent the metal skin from warping.

Deep Silver C6 Z51

It was a flaw in the construction of the roof by a GM supplier.

When I toured the Bowling Green assembly plant in September, there were boxes of painted tops sitting around waiting to being shipped back to the supplier.

PoundF15

Some engineer somewhere had to have thought about all the stuff we've been talking about already...

Doesn't surprise me to be a construction issue. Hopefully they've got new, better constructed ones, by the time my Coupe gets built here in the next couple weeks...

LS WON

Does this also apply to the translucent top?

LS WON

Will there be a recall? or will you just have to wait for it to happen and pursue it from that point? How about NHTSB similiar to the power steering hose recall?

Mocoso

Bryantt while your reasoning and explanation as to why it delaminated are based on sound principles I think that some of the assumptions you may have made could have been a little off. I dont think the upward forces generated by the pressure differential would be sufficient to stress or worse yet cause catastrophic failure to the adhesive. And I dont think the engineers at GM would have "given up" so easily on the bean counters trying to cut costs on such an obvious safety hazzard. Im siding on the faulty assembly over a faulty design camp.

Im glad they gave you a new top and sorry for your troubles.

o0 zeno 0o

Wow... An aerospace engineer, are we? Not quite I guess, as your technical outline is a little flawed. This is obviously a materials issue, not a design issue. While perhaps a change in design could compensate for the materials issue, it's pretty abusive to state that deformation at high speeds equals delamination due to bad design.

I think the real issue is your upset (and rightly so) that your vehicle had a defect that was improperly handled. The real fault lies with the dealer that did an inadiquate repair job. If it were in fact a bad design, then all our racing readers would be screaming by now.