iclick

Not fake news.

This will likely remain in deep classified mode unless GM is forced to release the info by legal means.

Yes, the latest appears to be 24280631, and although I haven't seen a report of this one failing yet it's only been available for several months. I don't follow the other forums for TC issues (Silverado, etc.), so I can't say what has been reported over there.

The TC part numbers I have are 24264542, 24273061, 24279495, 24280631--presumably in chronological order of release. The first three have shown to repeatedly fail in many cases.

Reflashes didn't fix my issues with shudder, tach oscillation, or delayed engagement. It did fix some hard-shifting symptoms in some cars, but my 2015 A8 never exhibited these.

Very early on before they got a handle on the problem, which was the TC. They now know the origin but unless the Rev. 3 TC is the magic bullet replacing the TC is still not a permanent fix.

After GM stopped replacing the entire tranny they went to the fluid replacement "fix." Not sure what fluid was used back then, but in his question/answer session about the A8 some time ago Tadge said the following:

The service bulletin you cite says to perform a double oil flush if you suspect that the trans is exhibiting TCC (torque converter clutch) shudder. That procedure has been successful in fixing a few vehicles. This has primarily been a truck issue, pretty rare on Corvette. The bulletin is now being updated to have the converters replaced instead of just a flush since it has not been 100% effective. So the bottom line is if customers are not having any problems, they shouldn’t worry about that document. In the rare instance where there is truly a torque converter problem, there is new design that should help. That hardware became available in December of 2015. I want to make sure customers with the prior design understand that if there is an issue, symptoms will appear early in the car’s life. The design change was not to improve the performance of the car or it’s durability over the long term. Bottom line is that if customers are not having a problem now, it is very unlikely to occur later.

Time has shown that some of these statements are not accurate. The newest fluid is Mobil 1 low-viscosity HD ATF (#19353429), and up until recently was part of the TC replacement fix. My guess is that they are getting hit with major service costs on replacing TCs and are trying this first, but I think many or all of those cars will eventually see a TC replacement.


I did and now have a new GS M7, which makes me very happy. I really liked my 2015 with the A8 even though I never warmed to the slushbox experience, but I can say that I'm really glad it's gone and the A8 issues are behind me. It's a shame because it was a great car marred by a flawed piece of corporate hardware, and that alone drove me away from that car. In early Jan. mine got the latest revision TC and fluid swap and worked perfect for one month before I traded it on my current ride.

djnice

The way I read it, as currently written the fluid flush service bulletin is not meant to address the RPM fluctuation issue. There is more than one torque converter issue GM is dealing with so it might help if you can clearly explain the problem so your dealer is using the correct TSB.

dmvette

Day 1 after triple flush - Drove close to 100 miles with no signs of TC shudder occurring.

Tomorrow will be interstate driving with cruise set around 70 for extended periods.




Got rained out today so interstate driving will be delayed!

djnice

Hey dmvette, Did you have RPM fluctuation or only shudder?

Always Red Dave

These tranny problems are ridiculous after 3 model years from 2015 - 2017 A8's. Bring on the A10 this month which I hope is released at the BASH in KENTUCKY! Hang in their guys and hopefully GM can get a permanent fix!

dmvette

I had the rpm fluctuation as well but it was only noticeable if you watched the tach while you was in cruise control set at around 70 mph or so.

The shudder started next and would happen while in cruise and when the car required a little throttle to maintain speed, it would shutter.

It progressed to shutter even when not set on cruise and just driving down city streets (45 mph). The shuddering itself also got worse as time went on.

So far, I haven't felt the shudder since the triple flush but need to drive more to test it out. I can't see how this would fix the shudder but so far, it has. I will update for sure if the shudder returns and what the mileage was.

lakemg

You're assuming that the A10 has no growing pains like the A8 and is going to be perfect right out of the box. The same assumption that we made with the A8 when it was introduced...

On edit: I respect and applaud the optimism, but it's just hard to be optimistic that the A10 is going to be perfect especially since Ford was involved...

Red C8 of Jax

Ford is currently having problems with the A10 and has stopped production of their new F150.

Always Red Dave

Maybe Ford can fix the A10 problem in the first year not like GM which is still looking for a fix on the A8 after 3 years. Listen I want to trade out of my 2014 A6 Z51 just not into a A8 unless GM comes up with a fix for 2018 !

69L79

How anyone who visits, even occasionally, this Forum can consider buying an A8 is beyond me. The A8 is to the C7 what the LS7 valve guide issue was to the C6 Z. A ticking time bomb. As these A8s continue to pile up mileage there will be more problems. GM should be ashamed of themselves. As for the A10, good luck with that.

Ernest_T

It takes a pretty large leap of faith to think GM can do a better job with the A10 than they did with the A8. I'm beginning to think its the AFM that is the issue and that the technology isn't there to stop the vibration in inherent in a V8 only running on 4 cylinders.

69L79

KemahGT

I have thought for some time that AFM, DOD, V4 mode, whatever you wanna call it is a factor in this surge and shudder fiasco. A big factor.

djnice

Ditto AFM. Trans tech is not available to support what they are trying to do. Gotta give GM some credit for trying to give us high HP cars and still meet the 2025 mpg deadline.

VLADIE22

listen.....ever since I have started running with the AFM disabler device I have had ZERO rpm fluctuations. So that is definitely part of the problem.

iclick

The M7 runs fine with AFM engaged, so I'm reluctant to blame AFM for all the A8 woes. It isn't AFM that's breaking, but is apparently the catalyst that's wreaking havoc with the A8 because of GM's efforts to mask the sensations, which they're not trying to do with the M7. The M7 does transmit a bit more vibration and transition bump into the cockpit when going into V4 and back, as there is no buffering going on at all, but not enough to create any emotional trauma--for me, anyway.

Maybe the smoke and mirrors they're employing to mask the sensations amounts to protection for more fragile A8 components. If so, they apparently haven't gotten a grip on a solution. If not, why not just quit trying? Tweaking the driving modes to disable AFM in Drive and, say, Sport or Track modes, would also help. I'm guessing there are reasons they don't do this, like fuel economy compliance, that is forcing some owners to buy third-party devices to disable AFM. Otherwise they would make it easier on themselves and make owners happier by loosening AFM programing.

Red C8 of Jax

After my new TC, I have no idea if I'm in V8 or V4, I feel no transition between the two. Sometimes I will check my computer just to see which one I'm in.

NSC5

AFM doesn't work well with the A8 because GM is trying to use the torque converter to reduce the transmission of engine vibrations to the rest of the powertrain and vehicle. The A8 itself does very well shifting quickly and holding power but trying to rapidly lock and unlock the mechanical lockup clutch in the torque converter multiple times per second is apparently beyond its ability to survive. AFM is active much more frequently in the A8 (compared to the M7) because vibration can be reduced to a tolerable level via this strategy.

Imagine how the M7 clutch would hold up if it were being engaged and disengaged multiple times per second. It is impossible to not have some wear when clutches and clutch packs are cycled and that can be seen through the ability of clutch to clutch architecture transmission (like the 8L90) to calibrate itself throughout its service life to adjust for the normal wear that occurs to the clutch packs that are used to choose the ratios available with this transmission. But these clutch packs aren't being constantly cycled at a very rapid rate like the clutch in the torque converter.

I expect that a converter clutch robust enough to properly withstand this strategy would be too big and heavy to be a good fit with the 8L90 in a passenger vehicle application. The torque converter clutch in the Allison 1000 (used in GM's diesel pickup applications) probably could withstand this sort of abuse since it is a very beefy unit designed to remain locked during full throttle heavy load operation but weight and size aren't a huge concern in that application.

ddelallata

I wish the new service bulletin would have also included RPM fluctuations as a criteria for the new triple-flush procedure. I'm hesitant to take mine in for this as mine is not shuddering yet and two local dealers claim to have never heard of A8 problems . I'm keeping the Range device plugged in for now. Mine is an 8/16 build date GS.

iclick

When I had my A8 I rarely felt V4/V8 transitions, either before or after my TC replacement. The new TC and fluid made no noticeable difference with that. My M7 transmits more transition bump and engine vibration than my A8 did, but I can only feel more vibration through the shifter. I also sometimes notice more tonal change between V4 and V8, whereas my A8 never did that. None of this bothers me at all and I do use Eco mode, which enables AFM, much of the time. If I could've had this setup in my A8, i.e. no smoke-and-mirrors engineering to mask the sensations and no reliability issues, I might've kept that car.