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There have been several postings on the A8 problems. I noticed the harsh downshift while the car was still under 3 years and in warranty. Reported it to the dealer at oil change time. I wanted it on record. Dealer smiled and thanked me for buying from them.
Now I am having the shudder and delayed engagement problems and went back to Dealer before the 5 yr powertrain warranty expires October 30,2019. Gave them the TSB numbers (Thanks to Stingray Forum for that info). They were all wishy washy about the flushing repair and wouldn't commit to the warranty repair. Also not sure if I was able to get a loaner. I explained forcibly that this is the cure and I want it done. Left the car on Wed before Labor day. Called numerous times for update. Got lots of answering machines. Finally got my service writer and let him know how I felt about the whole situation. Turns out the car had not been in the shop due to shortage of help, sick days, blah blah blah. I demanded my car be returned for the holiday because I knew no one would look at it for another 3 days. Tuesday following Labor Day I went in and had a long chat with my salesman who was very nice. Took the car in on Wed, and they all but rolled out a red carpet. Apparently someone got the message. One quick phone call to verify my loaner. I was in the shop and out of there in a few minutes. Was told parts on order would take 2-3 days. Was told they may even replace the entire transmission if GM determined it is more cost effective. I don't care. Just fix it. So far so good.
Here we are on Friday. No update from Dealer after my call for one. (Left a message of course.) I will stop in tomorrow for an update and will post my results here when the dust settles.

As a PS. I contacted another dealer in the area who I was told was savvy with all things Corvette. They wanted to charge me $135 diagnostic fee and had no cars for loaners if in warranty. "No cars? Isn't this a chevrolet dealer?" I said. That didn't go over well and I didn't even say goodbye when I hung up on them.
Good thing I am an easy going person.
 

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Sorry for your problems. I priced the fluid swap at last oil change. Was told about $400. I am going to do it as a proactive measure. Service person said he did it a few weeks ago on a problem vehicle and the owner said after a hundred miles of driving it was like a different car (for the better).
 

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The other thing I discovered was...after installing a new battery (that's another story) the transmission relearned my driving habits as opposed to the habits that were in there from the previous owner. But it still had the delayed engagement problem.
 

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I hate to be the bearer of bad news. I have gone through the same issue. My warranty expires 9/2020 and I got the trans flush at 38k and now I have 42k. I still have the shudder and was sold a new rim because they claim it was the reason for the shudder. After paying $900.00 for a new rim and waiting a month to get my car back, I took my car to another dealer and that dealer told me I had 3 bent rims. After explaining that I just paid for a new rim I was then told, go back to that dealer. I went to a private garage that road force balances wheels and was told my rims are not bent. This issue is known to GM and they refuse to do anything about it. After being given the run around, I went to a transmission shop and they advised me that my torque tube converter is bad (drive shaft). The dealer refuses to replace it because they continue to blame it on the rims. I wish you luck but I will most likely fork up $1200.00 rather than have GM and the dealership continue to blow smoke.
 

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Currently my C7 is sitting in the dealers shop waiting for a transmission person to handle the TSB regarding delayed engagement. In reading the fix it requires a transmission fluid flush as part of the TSB. While i did not notice any shudder issues I was told the trans fluid will be the replacement with Synthetic recommended in the TSB for the shudder fix.
Mean while my car has been sitting on the lot for a week. Time will tell..
 

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Sorry to read that 15snow-ray, hope it gets properly resolved shortly.
 

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I hate to be the bearer of bad news. I have gone through the same issue. My warranty expires 9/2020 and I got the trans flush at 38k and now I have 42k. I still have the shudder and was sold a new rim because they claim it was the reason for the shudder. After paying $900.00 for a new rim and waiting a month to get my car back, I took my car to another dealer and that dealer told me I had 3 bent rims. After explaining that I just paid for a new rim I was then told, go back to that dealer. I went to a private garage that road force balances wheels and was told my rims are not bent. This issue is known to GM and they refuse to do anything about it. After being given the run around, I went to a transmission shop and they advised me that my torque tube converter is bad (drive shaft). The dealer refuses to replace it because they continue to blame it on the rims. I wish you luck but I will most likely fork up $1200.00 rather than have GM and the dealership continue to blow smoke.
Kevin, bent wheels and the shudder are 2 different issues. I had a similar situation with 4 bent wheels and the transmission shudder. the dealer i used for service handled them separately. Since the flush i have driven from the DFW area to Bowling Green and back. A total of 1500 plus miles. The shudder is gone. The wheels were sent out and straightened. If you read the procedures to do the flush, there are other diagnostics involved. My shudder was very subtle. Stand your ground. I do know that the fluid has been a back order item. I waited a month after they told me it was approved. As my service adviser told me the had a “bunch” of them to do. The wheels on the GS and Z06 are a known issue. In talking with one of the GM engineers at the NCM 25th Anniversary celebration, he stated they have revised the testing procedures and beefed up the wheels on the C8. Doesn’t help us with the C7’s. My experience with the Bent wheels is 1 or more of them will eventually crack. That’s what happened the last time. I will most likely go to an after market wheel at that point.
 

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Discussion Starter #8
Got some good news today. I called the dealer (again) and finally got to talk to a live person. The Transmission is out and disassembled. They did not like what they saw and a new transmission was ordered from GM. It should be there today and installed. Not sure exactly what the diagnosis was. I want to talk to the tech in person for all the technical info. I also want to be sure they are installing the proper updated fluid. Stay tuned.....
 

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Final Chapter in this saga:
Got OUR15 back today. The Transmission was replaced with a new one from GM. Said there was nothing evident internally but GM said replace it. New synthetic fluid installed. Road test confirmed correct pressures and shift points, etc. They let it sit overnight and when it was started up this morning a loud banging/clanking was heard. After shutdown antifreeze was leaking. Apparently a piece of plastic was caught in the fan blade and shot into the radiator. Origin of the piece unknown. It looked like part of an electrical connector, but not from this car. No one knows. They replaced the Radiator and antifreeze at their expense and off I go. Hopefully this will be good now for a long time.:tickled_pink:
 

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All's well that ends well, and let's hope this continues to end well :)
 

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OUR15,
So sorry to hear this treatment. That's a horror story. I don't know any other providers of customer service who can readily get away with that.

I truly hope they get your pride and joy repaired and correctly. 🙏
 

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The performance or lack of, with the A8 is not a good sign for the ME C8. More reason to adopt a wait and see attitude. Sorry guys.
 

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So car sat for 10 days and was told they have confirmed the delayed engagement now and have started the repair. Another week at minimum for the repair and no word on the transmission flush as of yet. Flush requires about 24 quarts of synthetic fluid as they flush it 8 quarts at a time to get to a complete system flush of about 12 quarts in the system. considering just paying for it myself but goes against my grain to pay for something they know is their responsibility. And i have a pre paid service contract that includes a transmission flush . Don't like feeling like i have been taken advantage of like that.
Seems so ridiculous that they would not handle both issues while they had the car apart and the transmission sitting where they could handle the issue. So counterproductive in my opinion. Sadly this is what i was afraid of in opening this can of worms. Had a minor issue with the delayed engagement only when I first start the car up after sitting. Always happy with it after that. Now i have a car sitting in pieces on a shop floor and arguing with a polite service writer about handling the issue to completion before the car falls out of drive train warranty.
Trying to keep a positive attitude and looking forward to getting my girl back home and under my care . Hopefully in the same or better condition than when I handed it over to them.
 

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Discussion Starter #14
SNOWRAY... If your dealer is proactive, they may be waiting for the new transmission as did mine. According to the notes that were scribbled on my work order, GM said if you disassemble it and can't find anything obvious, Replace the trans. My dealer ran the diagnostic with car in gear and running through the shifting sequence. I saw the graph and it verified the problem with pressures, etc. Hopefully they will do the right thing. The replacement trans got the updated fluid and also includes the torque converter. So all the TSBs were covered. I have driven it only about 12 miles but am happy with the operation. Haven't tried the paddles yet. Will do that this weekend. I found that it is a bad idea to take it in previous to a holiday cause they will let it sit for the 3 days off. Also you get better results if you complain to all who will listen. Even if you are an even tempered person like me. This affair makes me glad I got the extended warranty which covers everything for another 40000 miles. So I am not concerned if the new transmission acts up again.
Good luck with your car.
 

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SNOWRAY... If your dealer is proactive, they may be waiting for the new transmission as did mine. According to the notes that were scribbled on my work order, GM said if you disassemble it and can't find anything obvious, Replace the trans. My dealer ran the diagnostic with car in gear and running through the shifting sequence. I saw the graph and it verified the problem with pressures, etc. Hopefully they will do the right thing. The replacement trans got the updated fluid and also includes the torque converter. So all the TSBs were covered. I have driven it only about 12 miles but am happy with the operation. Haven't tried the paddles yet. Will do that this weekend. I found that it is a bad idea to take it in previous to a holiday cause they will let it sit for the 3 days off. Also you get better results if you complain to all who will listen. Even if you are an even tempered person like me. This affair makes me glad I got the extended warranty which covers everything for another 40000 miles. So I am not concerned if the new transmission acts up again.
Good luck with your car.
Thank-you. In reading further the newest TSB on this issue is 16na364. In reading that I assume they will be checking several areas on the transmission for issues and without any positive results from those checks the fix is to replace the transmission. I'll follow up Monday to see where I stand.. Just glad I'm taking care of it now rather than next year when my drive train warranty expires. This would be a very large repair bill to swallow I am sure. Not rushing to go to the dealer as I'd be embarrassed to let them see me cry if I saw my beautiful Stingray in pieces all over the shop...:sorrow:
 

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My 2015 C7 with A8 transmission (26K miles) started shifting down to 1st gear with a "Thunk" when slowing down and come to a full stop. This was about 6 months ago. It was not severe and only did it 50% of the time, however, recently it has become more frequent.

My car was due for an oil change so I thought I would get the Thunk taken care of. I went in armed with the TSB #18-NA-355 dealing with the triple flush of fluids. However, the Corvette Tech specialist at the dealer said he would perform a complete diagnostic test before considering the TSB.

Much to my surprise and pleasure, the Tech found the problem was simply a software update #26400. He said he has performed this procedure in the past and it has always solved the problem.

So far, after one week, he was absolutely correct and the Thunk is gone.
 

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My 2015 C7 with A8 transmission (26K miles) started shifting down to 1st gear with a "Thunk" when slowing down and come to a full stop. This was about 6 months ago. It was not severe and only did it 50% of the time, however, recently it has become more frequent.

My car was due for an oil change so I thought I would get the Thunk taken care of. I went in armed with the TSB #18-NA-355 dealing with the triple flush of fluids. However, the Corvette Tech specialist at the dealer said he would perform a complete diagnostic test before considering the TSB.

Much to my surprise and pleasure, the Tech found the problem was simply a software update #26400. He said he has performed this procedure in the past and it has always solved the problem.

So far, after one week, he was absolutely correct and the Thunk is gone.
Now that is a nice outcome and one we have not seen (I don't recall, anyway) previously. Thanks for sharing Ron.
 

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Now that is a nice outcome and one we have not seen (I don't recall, anyway) previously. Thanks for sharing Ron.
I believe I posted about a similar problem with my transmission about 18 months ago. A software update corrected it. The update # was not listed on the invoice but the "transmission control claim module code" was 183D0.
 

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My 2015 C7 with A8 transmission (26K miles) started shifting down to 1st gear with a "Thunk" when slowing down and come to a full stop. This was about 6 months ago. It was not severe and only did it 50% of the time, however, recently it has become more frequent.

My car was due for an oil change so I thought I would get the Thunk taken care of. I went in armed with the TSB #18-NA-355 dealing with the triple flush of fluids. However, the Corvette Tech specialist at the dealer said he would perform a complete diagnostic test before considering the TSB.

Much to my surprise and pleasure, the Tech found the problem was simply a software update #26400. He said he has performed this procedure in the past and it has always solved the problem.

So far, after one week, he was absolutely correct and the Thunk is gone.
Actually, you don't even have to have it reprogrammed to fix this problem. The transmission can adaptively learn the new clutch pressures on its own over time. However, the software fix resolves the issue immediately, of course.
 
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