C6 owner here looking to get into a 2016 C7 in the next month or so. I want an A8, but am leery after seeing all of the problems. How is the best way to test for or find if a particular sample has problems or not? Is there any particular thing I could do on a test drive that would manifest itself? Thanks.

 

on the main dash screen, go to the screen where you can monitor if the car is in V8/V4 mode. Check for RPM fluctuations in V4 mode at steady speed driving on the highway or if there is a noise from the rear of the car that sounds like you are going over rumble strips.

 

In another thread here today, it's claimed that the slight fluctuations are normal and do not, by themselves, indicate a problem.

Confusing...

 

^^^ No, they are designed in but can also be out of normal operating conditions when the TC has issues.

Set cruise control to 65mph and drive for a little bit on smooth highway. Look for constant RPM fluctuations that are "unsettling". This is all in the feeling, there is no other way to judge besides hooking it up to the computers. If it doesn't feel right and the slips are too many, a tad bit violent, then be wary. If you like a certain car, test drive it then one or two others to compare in same conditions.

Also, ask them NOT to start the car overnight if possible, and go test first thing in the morning. Dont let the salesman turn it on at all until you get there. Once you arrive and start it up, look for a delayed engagement from park to drive (or reverse).

I know this is alot, but you asked how to check for issues and the above is the best way to do it.

 

Sure glad I have an M7!

 

The slight fluctuation of the rpm while switching in/out of V4 mode IS normal, but not when in V4 constantly.

When my torque converter failed it would fluctuate (and vibrate) while constantly in V4 mode with an ever so slight increase in speed that wouldn't put it into V8 mode. The easiest way to demo this for my tech was the put cruise control on, let it drop into V4, then whenever there was a slight change in elevation that required more gas, it would oscillate.

 

Loving my A8. 2016 Z51, built 10/15.

 

Gary, check the build date. GM changed some stuff in the trans, and the ones after 10/15 are suppose to be good to go. Yes, I know some have had problems even with those, but as they are mechanical things can go wrong with a few. My 03/16 build has been just fine. Paranoia has crept in with many here thinking every A8 was build in hell, and will completely detonate before they hit 5K miles. If it's pre-owned have the salesperson let you look at repair records for the car. If they look good don't be afraid to buy. Good luck.

 

The torque converter mechanical clutch is being continuously modulated in V4 mode to absorb the additional vibration that the engine generates in V4 mode. In theory the clutch is cycled at such a high rate that there is no noticeable or displayed RPM variance but I believe in reality the "squashed" torque converter clutch assembly that lets the 8L90 (aka A8) occupy the same space as the previous 6L90 (aka A6) doesn't hold up well to this operation and will start to vary in its locking characteristic over time creating the varying RPM and shudder.

You rarely see this issue showing up with Z06 owners where AFM is rarely active compared to the Stingray but I bet the issue starts showing up at higher mileage once the torque converter mechanical lock up clutch spends enough time being cycled. My Z06 will not be going into V4 mode.

 

OK, my reply is tongue-in-cheek. Mostly . . .


Buy the car and take off! Never visit the forum again unless you have a problem. OK, I obviously have not taken my own advice. My 2016 A8 has been fine, but read the forum too much and you will start to wonder if every little bump in the road is a slip, or a surge, etc. Try not to stare at the tach so much you hit someone. I too check it in V4 and V8 and have no oscillation like has been shown on videos.


When brand new I had a slightly rough 3/2/1 downshift in auto when coming to a full stop, but with just a couple hundred miles it learned to skip the 2 and just go 3/1.


And have some fun with manual shifting too. I go back and forth--around town maybe A8, but a spirited drive on curvy roads go M8. Using M more and more. Here is a fun link to manual shifting: LINK

 

I hate to be the voice of doom and gloom, but driving a 2015, 2016, or even a 2017 A8 once and observing no oscillation or shuddering doesn't mean it won't appear tomorrow or next month. I noticed the shudder in my 2015 when driving from the dealer when new in Feb. 2015, a 60-mile drive with 12 miles on the odometer when purchased. I didn't notice any tach oscillation but also didn't know to watch for it, as it was an unknown issue that far back, at least for me. The shuddering did not resurface until one year later on a sporadic basis, but once started it would go away after about 15 miles of highway driving. Thus, I never could demonstrate the problem to the dealer I used for service which was 35 miles away. After that it got progressively worse and by Dec. 2016 the car would shudder and oscillate any time it was in V4 mode at a constant speed. I had the TC/fluid fix done in Jan. 2017 but since they couldn't verify it at a dealer the delayed engagement problem that occurred rarely on my car was not dealt with.

What's more, if it gets fixed there also is no assurance a repair job will nix the problems for the long term, as some have reported having the job done twice as GM continues to experiment with new TC and fluid revisions. Nobody knows if even the current revisions are good fixes. My car got the #24280631 TC and #19353429 fluid and ran fine for the next month. The shudder was gone and tach oscillation reduced to just barely noticeable, no longer the rhythmic up and down movement seen before. The lack of certainty that it would be a definitive fix and GM's lack of interest in doing the o-ring upgrade for the delayed engagement while the tranny was out of the car exhausted my patience for what was otherwise a great car. In March of 2017 I traded it for a new GS M7 and I'm very happy indeed.

 

As mentioned, I'd look at the build date.

There's a very slight vibration that can occasionally be detected (honestly unless you're looking for it, it goes unnoticed) when going from v8 to v4 mode...and it's "normal".

I haven't experienced any issues with mine, other than a couple of hard shifts while coming to a stop. I blame it more on software than hardware. The A8 does an amazing job of predicting what a driver would naturally do (downshifting, upshifting, holding a gear) under various road conditions. Occasionally it will make a mistake.

I'm REALLY happy I chose the A8. I was concerned it would be lacking on the track, but after Spring Mountain, and living with the A8 for a year, I'd never choose a Tremec in its place.

Hopefully my A8 will hold up long-term...so far so good.

 

Chasing ghost ... If you want to find something you surely will. Enjoy the car ...

 

when I bought my 16 vert last august, I had no idea it would run on 4 cylinders. I would not have bought it had I known. it was over 3k miles before i read of troubles on this forum and found how to determine 4 cyl mode, I watch the dash now and still cannot feel shifting into and out of 4 cyl mode. the A8 transmission is that good! I'm climbing up to 7k miles daily...no regrets.

 

So you think this A8 issue isn't real maybe? I'd love to be a fly on the wall at the factory as the engineers try to figure this mess out. This is well documented at GM and I'm sure it's costing them. Mine is in the service dept. right now. The engineers at GM want to know why it failed, how it failed, and how to prevent it in the future. Perhaps they're finally growing weary of just throwing parts at this problem. They have to know this is a huge black eye for the company.

Now, I agree an owner that hasn't experienced any of these transmission shouldn't sit around worried that theirs will fail eventually, but that certainly doesn't mean it won't.

 

One test that is important, is to make sure the car has been sitting overnight and the engine is cold. Then start it up, put it into reverse(make sure everything is clear of you), give it some gas and see if it hesitates while the engine revs up, then slams into gear with a loud bang, and then shoots backwards like you are in a drag race.

A friend is on his 3rd C7 because of this problem. First car(2015) dumped the transmission with 4 miles on it(transmission replaced and friend refused to take delivery of it, even though he had just bought it), second (2015)dumped the transmission at 1200 miles(transmission replaced) and then started doing the same thing again in six months, so GM put him into a new 2016. He has around 3,000-4,000 miles on it and it's starting the shuddering problem. Last time I talked with him, he was going to take it to the dealer, and see if the fluid change would do any good.

But, even if the car drives right, it's no positive indicator that everything is all right with the transmission. Another friend's 2015 Z06 ran great(but did have the flex plate replaced earlier) up to 7,000 miles, when it decided to have it's transmission explode.



As you can see, that's not something that you can just accept and live with, even if you love your car more than you do your Pit Bull.

 

Mine is going in tomorrow for this very issue.
It was doing it every single day right up until I started having my phone ready to record the sumbitch doing it but wouldn't ya know it, now the sumbitch hasn't done it once!

Like the car is frackin with me and not how I like it neither.

I have the RPM thing too but the 2 minute delay from P to R was the most noticeable. Maybe if I stop trying to record it? lol

I told them I'll bring it in at 5pm and I'm keeping the key till the next day when I get there. Hopefully it does it but like so many other issues I've had them verify, verification and diagnosis can be mutually exclusive.