[basswilliamb@yahoo.com]

I purchased a 2017 RS for my son from a reputable dealer in South Florida with 14,000 miles on it. It now has 53,000. The vehicle is stock. We are feeling a vibration, rumbling, shaking, or hesitation at low RPM (1500 - 2000) regardless of the speed. Does not occur during automatic shifting. Happens temporarily and then quickly goes away. Even occurs on cruise control at 70 MPH. This is not an everyday occurrence, but intermittent. No check engine light. Ran a code at Autozone which showed something about Transmission Fluid Temperature Sensor which may or may not have anything to do with the vibration, rumbling, hesitation problem we are experiencing.

Does anyone have and thoughts or ideas on how to diagnose the problem and intervene with a fix?

[FarmerFran]

A8 shudder?

[Mark114]

A8 Shudder seems likely. TSB 18-NA-355

https://static.nhtsa.gov/odi/tsbs/20...63890-9999.pdf

[S.Macias]

Likely shudder. Sounds like what my car was doing. Do a transmission flush. Should fix it.

[arpad_m]

+1 on the previous posts, look up the TSB referenced above and head to a service department for a complete flush using the latest Mobil1 transmission fluid.

If this isn't a very frequent occurrence, chances are you can still save the original torque converter.

[SnakeEyeSS]

Another "A8 shudder" reply.

Glad I convinced a dealer to flush mine under warranty before it hit 1000 miles.

[basswilliamb@yahoo.com]

Thanks guys, you're the best. I even did a search on CHATGPT and came out with some other recommendations but the TSB 18-NA-355, and A8 shudder I believe are more likely than the solution Artificial Intelligence (AI) found. Will try the completeTransmission Flush with the latest Mobil 1 Transmission fluid and report back to the forum when completed. Much thanks again!!!

[CHASLT1]

I hear only 5% of A8's had probs. But that is all i see on the forums is shudder and this and that. I had it at 400 miles on a new 2019 C7 and now have a 2015 C7 that has never been touched and no shudder ever.

[arpad_m]

Originally Posted by CHASLT1

I hear only 5% of A8's had probs. But that is all i see on the forums is shudder and this and that. I had it at 400 miles on a new 2019 C7 and now have a 2015 C7 that has never been touched and no shudder ever.

Well, it's still a design flaw resulting in a much higher than desirable failure rate. There are many variables at play such as humidity, temperature, driving style and habits, mileage, likely even fluid and parts tolerance combinations, which explains why the hygroscopic nature of older fluids along with the factory tune does not immediately cause shudder on all A8 transmissions. Heck, some drivers may not even notice or care and live with it forever.

I had all available mitigating measures applied, including a proper tune, and never had the issue, my A8 works exceptionally well—this debacle is such a lost goodwill opportunity for GM, the 8L90 is a very good transmission that lost its initial great reputation entirely due to this stupid mistake.

One thing I've always wondered is if the 10L90 would shudder the same way if the same bad fluid and tune were used with it. We will never know, of course, but it's not an altogether different unit from the 8L90, nor is it a ground-up brand new design.

[cellsafemode]

if the shudder is strong enough that people other than the driver with their foot on the peddle can feel it, it might be too late for just a fluid replacement to fix. the torque converter gets glazed during these slip events and becomes permanently damaged over time. you have to do the change at the early onset, otherwise you have to do a fluid change + new converter.

make sure you get the good fluid when replacing. blue label, not black if using mobile 1.

anyone driving with fluid pre 2019 should change their fluid even if you don't have a problem. the issue in many environments is just a matter of time because it's due to the bad fluid used before 2019 that attracts water and the trans not reaching operating temps to boil it out over time.

[dmcmahan60]

A8 Transmission shudder and P0700, P0711 code which is a broken ribbon cable in the Transmission that is the temperature sensor cable And hopefully it did not do enough damage that it hurt the torque convertor. Let us know what happens.

[TP2SS]

Originally Posted by basswilliamb@yahoo.com

Thanks guys, you're the best. I even did a search on CHATGPT and came out with some other recommendations but the TSB 18-NA-355, and A8 shudder I believe are more likely than the solution Artificial Intelligence (AI) found. Will try the completeTransmission Flush with the latest Mobil 1 Transmission fluid and report back to the forum when completed. Much thanks again!!!

Not sure if you intend to do this yourself, but don't! It is a special procedure done with special equipment at the dealer (all outlined in the full TSB). It should be about $450 out of pocket since your PTW is long gone. DIY this and if it doesn't work it's gonna cost you a lot more than $450! Don't wait to get this done if the shudder just started. The longer you wait, the more damage is done and then you'll need a TC too.

Originally Posted by cellsafemode

if the shudder is strong enough that people other than the driver with their foot on the peddle can feel it, it might be too late for just a fluid replacement to fix. the torque converter gets glazed during these slip events and becomes permanently damaged over time. you have to do the change at the early onset, otherwise you have to do a fluid change + new converter.

make sure you get the good fluid when replacing. blue label, not black if using mobile 1.

anyone driving with fluid pre 2019 should change their fluid even if you don't have a problem. the issue in many environments is just a matter of time because it's due to the bad fluid used before 2019 that attracts water and the trans not reaching operating temps to boil it out over time.

Not entirely true about the first part. My wife's '16 CTS started doing it around 41k and she mentioned the "weird shake" to me. It'd been doing it for a week or two she said. I knew what it was before driving it myself and confirming it. It went to the Caddy dealer the next day. No problems since and it's at 63k now. Great advice on the last part. I tell everyone with an A8 to do this as well. I did my '16 SS, still under PTW, in 2020 with around 4k. Never had the shudder, just did it as preventative. Had to argue with the dealer about "verification" but when I pointed out the text of the TSB they relented and did it under PTW.

[plus1zero]

Yup A8 shudder. I've had several GMs with an A8 and they all do it at some point. Tranny flush will fix it.

[Hyper Blue RS]

My 2018 RS has 46k miles and just started the shutter last week. Maybe the Louisiana heat and humidity of the last two weeks finally got to it? Went to a well respected transmission shop who dropped the pan, changed the filter and put all new fluid. They told me that the magnet at the bottom of the pan did not have any metal on it at all. So far, the car is driving good, without the shutter.