I redid the numbers using that format and got 18 of 127 complaints from 2020 through 2024 were related to DCT issues.

 

Yes, I was referring to these aftermarket warranties. The GM Warranties are the most dependable.

 

Yeah if only 18 DCTs issues out of the 100k plus C8s on the road. The C8 DCT would be the most reliable transmission know to man kind. In the past 15 mins I’ve come across two additional DTC failure issues on the forum within the past 30 days. One of them was the second C8 from a DCT failure buyback.

 

 

Or Rick "Nature Boy" Flair (Flare)?

 

It's rare but has happened. A member on the "other" C8 forum had his DCT replaced 4 times.

 

I'm not going to comment on whether or not "major transmission issues" are "widespead". I don't even know that other means (0.5%, 1%, 2%,10%) when they use that term, and even if I did, I don't have enough data to estimate the percent of C8 (there are 195000) that have had a major transmission issue. The only statistical data we have is consumer reports data which is based on C8 owner reports, and its been verified that consumers only reports on vehicles with sufficient miles, and its compared with other vehicles with similar mile (I mention this because some were dismissing the data say it was not representative because C8 are not driven as much as others). And based on owner reports, the rate of major transmission issue for the C8 is average or above compared with other vehicles in its group. Even so, we do not know what the average rate of major transmission issues is, so we still cannot say whether it 1%, 5%, or whatever.

I question whether NHTSA reports are completely representative of the known transmission issues, widespread or not. Isn't the NHTSA mostly about safety related defect? The Z06 fire issue was limited to a very, very few cars but it was a major issue and recall. But there are plenty of GM documents of C8 transmission issues - widespread or not. I would think that to warrant a bulletin, or customer satisfaction report, or nhtsa report there would need to be a significant percentage of transmissions that manifest or could manifest the issue. We don't know what the percentage warranting bulletin or report is - and not everyone would agree on whether it was widespread or not. I can think of a few examples of documented issue though:

Case Porosity - GM Service Bulletin Bulletin No.: 22-NA-173. I think this is resolved, but there may have been few early on.

Park Pawl Sensor Drift - Bulletin No.: 23-NA-176- Enough to warrant a bulletin and now there are parts available so it can be repaired in the field.

Transmission Pan Gasket Leak on early model - don't know if there was a bulletin but the original stamped pan was replaced with a case pan, with slightly different bolt pattern. However the cast pan can still be retrofitted to the earlier transmission cases to solve the problem. There were enough of these to warrant the design change to the cast pan.

Internal transmission solenoid or switch sticking due to debris - Bulletin No.: 21-NA-033 - the symptom of this problem was one or more DTCs set, and it was remedied by executing a series of Transmission Service Cleaning Procedures, followed by the infamous Hydraulic System Flush. Enough cased of issues caused by debris to warrant a bulletin. And later versions of the bulletin indicated that the service manual was updated to deal with the list of DTCs.

Shift Fork Position Sensor Issue - this was discussed in a tech-link article:
https://gm-techlink.com/?p=14615 At the time this was not repairable in the field. I do not know if that is still the case.

Customer Satisfaction Program N242435630 Serial Data Gateway Module

Clutch Replacements - there have been a few cases of replacement of clutches and/or related clutch components.

Axle shaft seal leaks - I have seen reports of that on the forum.

I'm sure others can add to this list.

 

@Andybump This is true, but a little off the point I was making. I'm not interested in "us" trying to figure out the stats of transmission failures or in consumer reports publishing that data. I'm just trying to encourage folks who have had transmission issues to report them to the NHTSA so that the NHTSA can decided if an investigation is warranted. If an investigation is opened, GM would have to address it and the information would most likely be published (I assume). To be clear, I'm not claiming there should or shouldn't be an investigation. I have only noted that (as another forum member point out), 18 transmission issues have been reported 2020-2024 for the C8. We know there have been so many more that which gone unreported. When compared to the L87 engine failures in the Tohoe 21-23 for example, 245 engine failures were reported. These reports (along with other models using the L87), sparked an investigation which lead to GM having to acknowledge and address it. Now I have know idea how many C8 transmission have been replaced, or how many buyback there have been. I just wonder if the real numbers, if reported, would garner attention from the NHTSA.

 

Yes, I was apparently under a misconception about what you meant. When you spoke of pulling NHTSA reports, I thought you were talking about the reports the the NHTSA puts out. Which are generally the result of an investigation that started with some reports or observation from wherever. But it seems you were referring to some record of the actual individual reports made to NHTSA. I think for example, there were less than a handful that resulted in the identification and investigation of the Z06 fire hazard. So, what you are saying is that you have access to or a link to a site where we can see the entire list of "complaints' lodged by individuals, and in that list you find 18 reports to the NHTSA about C8 transmission issues.


Can you provide a link to the source so that we can see the types of transmission issues reported the NHTSA?

Interestingly, the number of vehicles affected by SUV/truck sudden engine failure was on the order of 877000, so 245 reports would be just 0.028% reporting rate for this "widespread" issue. Pretty darn small. There are only about 195000 C8s on the road. If every single one of them is affected by a "major transmission issue" (and what could be more widespread than that?) this same reporting rate would be a mere 54 reports and we already have 18 you said. I don't know how many it takes to trigger an investigation, but the Z06 fire issue was from only 3 or 4 reports.

I think most folks are under the impression that the NHTSA is interested in safety related issues - ones that result in injury or death, and perhaps that's why there are so few reports. The Z06 fire thing was considered a safety issue and it required very few reports. The report was "I was putting gas in my car and it blew up". The SUV issue was considered a safety issue because the engines could, and did, fail suddenly creating an instant traffic hazard. The reports were "I was driving down the road at 60 mph and the engine failed, my power steering and power brakes failed, and it was dangerous". During the investigation that GM was required to do by the NHTSA, after the initial reports to the NHTSA that you cited, GM investigated 28,102 field complaints or incidents in the US potentially related to failure of the L87 engine due to crankshaft, connecting rod, or engine bearing failure, of which 14,332 involved allegations of loss of propulsion. GM identified 12 potentially related alleged crashes and 12 potentially related alleged injuries in the U.S. So this was a safety issue and widespread. This information appears in the report that GM made to the NHTSA.
https://lemberglaw.com/wp-content/up...5V274-1938.pdf

I think the majority of the transmission issues start with the appearance of a MIL on the DIC, or maybe a fluid leak on the garage floor, maybe some odd behavior - the owner takes the car in - and it gets repaired or replaced, under warranty. Sometimes the repair is a Hydraulic System Flush - or a valve body replacement - or a clutch replacement, a seal replacment, or even transmission replacement. The owner may not ever know what the issue was. The report an owner would make to the NHTSA would be something like "I had MIL on my dash, took it to the dealer and they replaced my transmission under warranty", or "I had transmission fluid leak, took it to the dealer and they replaced an axle seal under the warranty", or "I got message that said idle creep disabled, took it to the dealer, and they replaced the valve body under warranty", or "I had a transmission problem and the dealer could not fix it so they bought the car back under the lemon law" .

I'm not for keeping any of this a secret.... and I'm interested in whether the percentage of such issues indicates a significant reliability problem, or is just the average rate of "major transmission issue", which was the motivation for your suggestion. I'm just wondering if this is what that agency investigates? And yes, I think one could argue that the transmission could fail suddenly driving down the road and create a traffic hazard, but that is not the typical way the transmission issues are manifesting.

 

Here is a link to a site that discusses reporting of issues to the NHTSA , and another link to the page where one can report an issue. Among the things said on the first link is this:

"What Problems Should You Report to the NHTSA?

Vehicle manufacturing defects can be divided into three general categories: safety problems, utility problems, and value problems. All three issues could be grounds for a California lemon claim, but the NHTSA doesn’t necessarily care about them equally.

Value problems are typically the least important, and the NHTSA rarely acts on them. For example, if your vehicle’s paint starts peeling after six months, that’s annoying and may hurt the vehicle’s value. However, it’s unlikely to put you or other drivers at risk. You can report the issue to the NHTSA, but it probably won’t lead to an investigation.

Utility problems are more serious. These are issues that prevent you from using your vehicle in ways you might reasonably expect. For example, if your window switches are defective and you can’t roll them down, or if your locks jam and you can’t secure the vehicle, those are utility defects. It may be worth reporting these because utility and safety problems often overlap.

Finally, safety problems are the most severe. These issues may or may not look serious at first, but they make accidents, injuries, or fatalities more likely. Examples range from inaccurate warning labels to faulty backup cameras to wiring defects to pedals that jam. These issues are always worth reporting to the NHTSA. "

Here is the link to that site:
https://calemonlawguys.com/how-to-fi...defective-car/

And here is the link to the page where on can report an issue:
https://www.nhtsa.gov/report-a-safet...le-information

 

Here is a link to the filing process. I'm neither recommending nor discouraging anyone from filing a complaint, but I was not aware of the process so I looked into it and thought I would share it.
https://www.nhtsa.gov/sites/nhtsa.go...nttorecall.pdf

And here is a link to a sample completed form.
https://static.nhtsa.gov/complaints/...E8789808C8.pdf

 

@Andybump Here is the link to my source. Its pulls NHTSA reports that are public.

https://thecarguyonline.com/CHEVROLET/CORVETTE/2020

 

Here is the link to the NHTSA site that lists the transmission related complaints. You can read each complaint in detail here. I count 17. They are all over the place. I used the keyword transmission, but some of them appear to be about other issues. One at least I recognize from the forum - about a fire that may or may not have been caused by a rag left in the engine bay.

https://www.nhtsa.gov/recalls?keywor...Model=CORVETTE

 

Thankyou. Yes, I found the direct link to the NHTSA page that allows that search - and posted it above.

 

I totally agree, it is best to keep track of the service bulletins like TSB 22-NA-173. I was able to get my 2025 Z06 engine oil leak fixed #1 because it is still under warranty but #2 because of the service bulletin. In my first year (4,700 miles) of ownership the one issue has been solved by the factory, and the car is strong and flawless. The car is mechanical and things could go wrong (human error) either at the factory or by the hands of the owner. I also had a C7 Z06 and never had any issues but I am also conscious and wait for all temps (including tires) to be at normal temperature before pushing it. My C7 did a 168 MPH at the Texas mile, again, no issues. And while I favor Japanese cars for their reliability I have to admit that the C8 is a great choice for the money. I’m lucky to have the best of both worlds.