I had surmised that may years ago (C6 era), without any knowledge of the study. Non-like materials have different and varying expansion rates. Leather and the underlying synthetics evidently have different rates. As the various materials expand and contract the glue will "shear" as it has no choice but to do so, hence delamination occurs.

 

YES....That was part of the conclusion of this study. That leather can expand (and contract) at a faster rate than the underlying substrate and glue thus shearing the glue bond, where a synthetic material has less expansion and contraction. However, when the temperature changes are more gradual, where the substrate and glue can also change at a similar slower pace with the leather, then then bond holds.

 

Yep, this problem is 3 generations old

 

Yes, I don't disagree...This could be one of the causes for delamination failure due to either improper adhesive application or simply the selection of the wrong adhesive type which will not hold up to those environmental changes... If that's the case you'd think after all these years they would have resolved this issue by now!

 

So, if you drive your car for three hours on a 95 degree day with the cabin closed and AC on, then park it in the sun and shut if off, the interior temperature will rise from a comfortable 70 degrees to 114 degrees in 10 minutes and continue to get much, much hotter. And its probably even hotter on the surface of the dash leather if a windshield cover was not used. But underneath of the leather ( what folks are calling a substrate) that part is not nearly has hot. So even if the layers did change at the same rate with temperature, the temperatures are significantly different. It gets perceived as a heat problem because hot days are the ones that will cause this rapid temperature increase.

 

If this was the only cause then it doesn't explain why some garage queens (or new cars at a dealer with only a few miles on them) have the problem but many daily drivers and non-garaged cars all over the country don't have the problem.

 

Actually, this is not true.

The reason the engineering study was conducted was because management was paying for dash replacements. Management dispatched the engineering team because it wanted to know if there was an inherent manufacturing flaw, one that quality control was not reporting (or missing) such as - improper application of the adhesive in the assembly process.

The wrong type of adhesive is not possible if the manufacturing and design processes are being followed. Coming from a manufacturing engineering background, only the correct adhesive would be kept in that assembly area. Like any modern assembly process, if all the parts are not there (the correct glue in this case) manufacturing would not occur. The glue itself could be the correct glue, but be a bad batch. That was also looked at and QC controls on that raw material proved to be consistently good.

Bottom line - the study was conducted to determine if there was a manufacturing problem or an environmental one (either before, or after the product left the controls of the process, or both). The study concluded the defect was an environmental cause, and NOT a manufacturing one.

 

The "new car in the dealer showroom" is one of the poorest examples I've heard. Where was the car before it was driven into the showroom? Could it have been sitting outside in the lot, in the open environment for days before it was moved? What does mileage have to do with it? A brand new car with 4 miles on it could sit in an outside lot for 2 years and have much more environmental damage than just a delaminated dash. If it was moved into a showroom with 4 miles on it and you saw it THEN, how could you evaluate the damage you now see by mileage? Or conclude it has been sitting in the showroom for the last 2 years?

Garage queens are a perfect example if you're understanding the conclusion correctly - My garage can be 75*F still be the middle of the day when it is a clear bright sunny day and air temp outside reaching 85*. If I pull my car out in the driveway (from 75*) with the dashboard exposed to the full sun, roll up the windows and lock the car, how much TIME will it take to get the surface of the leather up to way over 100* while the glue and substrate are still possibly in the 75* to 80* range? It is this rapid temperature change that does the damage and causes the leather to shear from the glue. Not whether the car is a garage queen or a DD.

 

So...if this is true, you realize the flaw in your previous comment about "the wrong glue"?

 

Not flawed at all...

If it was an environmental problem, then the design engineers either have not selected the correct adhesive or designed the correct manufacturing processes used in manufacture to ensure this bond holds up under all conditions.

 

I would say (and I am no expert in the upholstery industry) since EVERY manufacturer, bar none, that sells cars with leather dashes, ALL have this delamination problem and all must be using the industry standard products, there is no better glue out there that they are all missing.

 

Do you have a link to this study? It doesn't seem to fit the C8 scenario where some cars don't have the problem and especially the infant mortality cases on some vehicles.

In the C8 case it could be a manufacturing problem especially if the necessary mistake proofing hasn't been put in place. What if all of the dashes go down the same assembly line but the 3LT dash material requires a different adhesive application process or different adhesive? A worker could incorrectly use a 1LT/2LT process/adhesive if the proper mistake proofing isn't in place. Or perhaps the same process/adhesive is used on all dashes but the process needs to be more tightly controlled for the 3LT dash components. Or perhaps it is variability in the 3LT dash material (which appears to be a bonded leather vs whole animal hide).

If it is just thermal cycling then there would be some consistency when the dash debonds after a certain number/magnitude of thermal cycles.

 

Yes, GM could have a manufacturing problem. It wouldn't be the first one. Look at the DCT, how it started out in mfg. This manufacturer wanted to ensure they did not, and if they did that it was corrected. Sadly, they found nothing in their process to correct.

The study is not public. In fact I only saw the conclusion excerpt, not the complete study which is under lock and key as any internal study like this with any manufacturer would be. I happen to have contact with an insider at one of the mfgrs. I thought it would be valuable to share in this forum since this issue comes up pretty consistently. The results of this study caused me to treat my car with an expensive leather dash to add some simple precautions when my car is out there. So far, so good! Maybe some here might try it.

Still, everyone leaves here drawing their own conclusions. I have no interests in trying to change anyone's mind, just offer additional insight that can either be accepted, challenged or ignored. I'm OK with any of those outcomes.

 

I just can't picture how some cars that only have a few miles on them went through more extreme thermal cycling conditions than thousands of high mileage daily drivers constantly exposed to the elements. You will definitely see more rapid and higher magnitude thermal cycles when a car is consistently parked outside for years in cold or heat and the AC or heat is turned to drive than you will on a low mileage car parked in a garage in the same part of the country.

 

Sounds as if GM simply has not focused enough time and resources on resolving the problem with their suppliers who manufacture the leather dash...Also, good design practice takes into account environmental conditions that the part will be subjected to so that should be no excuse for failure if designed properly...

The fact that there are many examples of dashes that do manage to survive a lifetime with no signs delamination while a few others fail points to a control problem due to either design, manufacturing, or material...

This is clearly not something any of us are going to resolve...But it is extremely frustrating to many who have had to go through this problem for years...If GM can't manage to fix this with their suppliers, then they should not offer it at all to customers...

 

Rapid Blue, its not dark

 

Frankly, I've had cars with, without leather dashes. Leather (animal dead skin) is not something that moves me like it does some people. All the Vettes I've had were without. The playcar I drive now simply doesn't come with anything but leather dash, so did my Bentley CGT, my AMG GTS, etc.

It is interesting to me that with all the dash leather separating there is no match on door cards with leather, consoles, seats (maybe bad example) even steering wheels (mostly), only the dash leather that, coincidentally, has the most environmental exposure in the car.
Just a few other examples - Bentley, Aston, Bentley again, Ferrari, Jaguar:

 

I still don't see an answer to the question:

why has this been happening since the 4LT option that was begun in the 2008 model of C6 and the problem of "dash separation" still exists 17 model years later, through 3 generations of cars produced?

and with all due respect to "tadda"---
"Sounds as if GM simply has not focused enough time and resources on resolving the problem with their suppliers who manufacture the leather dash...Also, good design practice takes into account environmental conditions that the part will be subjected to so that should be no excuse for failure if designed properly."

To my knowledge it isn't GM's problem to solve because they don't make or apply the materials. It's done by an outside firm contracted to manufacture the upholstered dash. Plus, after 17 years and 3 generations of just Corvettes (not incl. other brands) it's not just a little problem---it should be embarrassing. To someone.

 

Yes, I understand that it's outsourced to other suppliers....However, GM is still responsible in the end...

Here is the statement I made...Note the highlighted part below ..

Meaning that if a problem exists with any supplier, then GM's Supplier Quality Team is tasked with working with the supplier / contractor to resolve the problem...

For example "if" extreme temperature cycling or high heat is a concern then GMs team should recommend to the supplier that they periodically pull samples and run temp cycling and high temp heat soak stress tests to ensure the manufacturing process is under control...

 

My 2010 still has not experienced this. Perhaps it was repaired by the first owner. I have no idea. But it sometimes keeps me up at night regardless.