[Melze]

Out of nowhere, last week my 30,000 mile 2016 ATS began exhibiting the dreaded shudder. At first I thought I had run over a long rumble strip, but I was soon able to provoke it by "feathering" the throttle, and stop it with a downshift, so I knew I had fallen victim to what seems to be a universal problem with the new 8 speed transmissions. I called my dealer and they said to bring it in the next day. Got the car back the same day. The service writer (and the work order) said they flushed the transmission 3 times, and filled it with GM part # 19417577 which is the latest iteration of Mobil 1 LV HP transmission fluid with a modified anti-shear additive. It seems to have worked. The shudder is gone and (subjectively) WOT upshifts feel more positive. Now the question is how long will it last?

One piece of advice I have is that if you begin to experience the shudder, get the fluid flushed and refilled ASAP. The shuddering will eventually burnish the internal clutches to the point where the torque converter has to be replaced. Instead of a couple or 3 hours work, you're talking about major downtime waiting for parts and then major work. Hopefully this new fluid is the effective cure.

 

[rsingl]

Does your 2016 ATS have an AFM (active fuel management, drops cylinders under light load including highway cruising) equipped engine? If so, do yourself a favor and install a Range anti-AFM module in the OBD II port to prevent AFM from going active. The Range module does NOT change the ECM programming but simply tells the system that one of the many environmental variables necessary for AFM to go active has not been met.

When AFM is active, the torque converter lockup clutch is continuously and actively modulated to reduce the transfer of engine vibration to the rest of the powertrain and the passenger cabin. AFM makes shudder more likely and increases wear of the lockup clutch.

The current GM explanation is all previous versions (there have been many) of ATF used in the 8Lxx series transmissions were hygroscopic and they blame the shudder on this. It has gotten bad enough that the dealer is no longer required to test and verify shudder (nor will they be reimbursed under warranty for this diagnosis work) but simply to do a one time replacement based upon customer complaint. The triple flush is no longer required however the single transfusion process is equivalent to it; it is really more semantics because a complete exchange of fluid still occurs.

My 2016 Z06 still has the first iteration of fluid in the second generation torque converter with no problem but it has never been allowed to run in V4 mode and it will get the new fluid when it comes out of hibernation in Spring.

Rodger

 

[RonBaker]

"One piece of advice I have is that if you begin to experience the shudder, get the fluid flushed and refilled ASAP. The shuddering will eventually burnish the internal clutches to the point where the torque converter has to be replaced."

My condolences Melze, once you feel it it's always on your mind. Your advice above is good advice and is the only option available. From everything I've researched the fluid exchange simply removes any metal shaving already present and masks the shudder. Most of those who have had the shudder then had one or multiple fluid exchanges had the shudder reoccur, usually soon after the exchange.

The anticipated potential solution supposedly to be released Q1 2019 (mentioned below) turned out to be yet another iteration of the fluid exchange. There is no known solution except to continually exchange fluid when shudder presents and ultimately replace the converter with another of exactly the same design.

"(4). GM has known about the Transmission Defect for years, since right after introduction of the transmission. Since 2015, GM has issued thirteen versions of a “technical service bulletin,” or “TSB,” related to this shifting issue alone. A TSB is an alert to dealerships, informing them of a potential problem in a GM product and advising them how to address the problem when customers complain to GM dealerships. The TSBs related to the transmission issue have advised dealerships to, among other things: complete the “clutch drive learn procedure,” replace the valve body, replace the entire transmission, flush the cooler lines and cooler, remove debris from and clean the transmission pan, replace the transmission filter, replace the transmission fluid, and flush the transmission.

(5). While the problem is known, the solution is not. None of GM’s suggested repairs have remedied the problem. Some recent repair orders found by Plaintiffs’ counsel note that “GM is aware of concern and a release date of late January/February to correct issue.” Another noted, “no repair available until quarter 1 in 2019.” But current purchasers and lessees should not have to cross their fingers for a fix, and prospective customers should be told of GM’s awareness of a defect. Presently, it appears GM is merely biding time until its warranty expires."

https://www.classaction.org/media/duffy-et-al-v-general-motors-inc.pdf

 

[Melze]

Does your 2016 ATS have an AFM (active fuel management, drops cylinders under light load including highway cruising) equipped engine? If so, do yourself a favor and install a Range anti-AFM module in the OBD II port to prevent AFM from going active. The Range module does NOT change the ECM programming but simply tells the system that one of the many environmental variables necessary for AFM to go active has not been met.

When AFM is active, the torque converter lockup clutch is continuously and actively modulated to reduce the transfer of engine vibration to the rest of the powertrain and the passenger cabin. AFM makes shudder more likely and increases wear of the lockup clutch.

The current GM explanation is all previous versions (there have been many) of ATF used in the 8Lxx series transmissions were hygroscopic and they blame the shudder on this. It has gotten bad enough that the dealer is no longer required to test and verify shudder (nor will they be reimbursed under warranty for this diagnosis work) but simply to do a one time replacement based upon customer complaint. The triple flush is no longer required however the single transfusion process is equivalent to it; it is really more semantics because a complete exchange of fluid still occurs.

My 2016 Z06 still has the first iteration of fluid in the second generation torque converter with no problem but it has never been allowed to run in V4 mode and it will get the new fluid when it comes out of hibernation in Spring.

Rodger

Thanks for the informative reply. My ATS is a 2 liter Turbo and does not have the active management "feature". Some of the guys at Mobil talk about greater shear resistance in the new iteration of the fluid as well as well as enhanced resistance to water absorption. In the end, however, it all seems like bandages being applied to remedy a mistake in design. I wonder if the new 10 speeds are going to exhibit similar problems.

 

[rsingl]

Thanks for the informative reply. My ATS is a 2 liter Turbo and does not have the active management "feature". Some of the guys at Mobil talk about greater shear resistance in the new iteration of the fluid as well as well as enhanced resistance to water absorption. In the end, however, it all seems like bandages being applied to remedy a mistake in design. I wonder if the new 10 speeds are going to exhibit similar problems.

You are welcome and be happy that you don't have AFM because it is a Rube Goldberg style mess. I suspect the 10 speed is probably OK because vehicles were designed around it while the 8L90 (and 8L45 little brother) were designed to fit the same mounting space as their 6Lxx predecessors and part of the strategy to make it fit was to shrink the amount of space allowed for the torque converter resulting in what GM called a squashed torque converter. Apparently torque converters (or at least the clutches used for the lockup function) don't like being squashed

Rodger

 

[HP52TA]

Has anyone tried this product as an additive?

https://www.lubegard.com/wp-content/uploads/2019/07/GM-8-speed-shudder-flyer_all_sizes.pdf

I have been experiencing the intermittent shudder and 1-2 shift issues as well in a 2017.

 

[Melze]

Has anyone tried this product as an additive?

https://www.lubegard.com/wp-content/uploads/2019/07/GM-8-speed-shudder-flyer_all_sizes.pdf

I have been experiencing the intermittent shudder and 1-2 shift issues as well in a 2017.

That hard 1-2 shift is probably not good for the longevity of the transmission and I don't think there will ever be a mechanical fix for it. But if you take 15 seconds on a cold start to manually shift from 1st to 2nd and wait a few seconds while in second gear, you can then shift back to automatic and the harsh 1-2 upshift will have been eliminated.

 

[rsingl]

That hard 1-2 shift is probably not good for the longevity of the transmission and I don't think there will ever be a mechanical fix for it. But if you take 15 seconds on a cold start to manually shift from 1st to 2nd and wait a few seconds while in second gear, you can then shift back to automatic and the harsh 1-2 upshift will have been eliminated.

That hard shift is definitely not good and it will glaze the associated clutch pack, there have been a few replaced in Corvette applications because of this issue. And it doesn't even take 15 seconds; I remote start my Z06 and by the time I am belted in the engine has already dropped to curb idle. I then back out of the garage, put the transmission into manual (where it generally stays) with the brake applied, paddle up to second and then paddle back to first. Literally 1 second is sufficient to fill that clutch pack actuator but you want the engine to have dropped to its base idle speed before you do this quick shift in and out of second.

Once done, you shouldn't need to go through this process again until it sits overnight. And all GM needed to do was a quick software update to do a partial pre-fill of that clutch pack at initial start. They solved the same issue with the same initial lazy shift of the Allison 1000 transmission after a cold start almost two decades ago. The 8Lxx family also pre-stages next anticipated clutch packs during hard acceleration which is one of the strategies used to provide shift completion speed in line with a DCT transmission so they are doing this anyway for other parts of the operating cycle of the transmission.

Rodger