Help Torque converter problem

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Trussie

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Need some help…. We think we’ve diagnosed our problem via Google ( yes- I know…). Torque converter issue- the symptom is a distinct feeling of driving over rumble strips. It occurs anywhere from 40+ km/hr up to highway speeds, but not during acceleration or when the foot is not on gas….but does occur when foot is on gas maintaining a consistent drive speed. Dealer is not much help as they want to replace spark plugs.
Car: 2016 Stingray LT1 with no mods with 19,100km on it. It’s never seen rain, only best fuel used, stored in heated garage…. it’s babied! We noticed it start last summer and got spark plug suggestion to fix. It’s a little worse this season since putting her on the road 2 weeks ago.
I’d like to know:
1- spark plugs are not the fix, correct?
2- a reputable shop in Barrie or surrounding area that can fix
3- safe to drive to get it there?
Thanks all!
 
As you've already discovered, this is a well documented issue with the C7 as it relates to the 8L90 transmission. What you've described is the infamous "shudder" and, yes, it is related to the torque converter. The possible good news is that, from what you've described and based on your mileage, you may have caught it early in the development stage. Given that your vehicle is a 2016 it's most likely that the original ATF is the culprit and, as such, would be the most logical first step in solving the problem. However, there have been a number of component modifications and improvements relative to this problem. Valve modulator bodies, torque converters and, of course, ATF's, since the 2016 MY that have helped to improve the problem. I'd start with the ATF triple flush.

To test this theory, activate speed control at about 100 kph with the car in full auto, "D". Determine that it is shuddering. If yes, repeat the process in "M", manual mode. Does the shuddering stop? If yes then it's very likely that the problem is the ATF. If no then it's a different issue.

Just a few points of clarification on this issue. First off, the torque converter "shudder", as related to the 8L90 8 speed automatic transmission, is caused by the operation of the Active Fuel Management System (AFM). The problem occurs because the lock-up clutch in the torque converter fails to lock completely during the change from V8 to V4 mode. This is now thought to be due to excessive moisture absorption by the ATF, or so says the latest from GM. They have gone through 3 different formulations of Mobil 1 Synthetic ATF with the third, and so far final version, being the most successful. The general consensus is that the latest triple flush approach with the newest ATF (see attached TSB) will, in most cases, solve the problem.

As for the dealer not being familiar with this problem, not surprising. Try to talk to a senior service staff member or an experienced Corvette tech. Mention the triple flush for the 8L90 transmission and show them the TSB. Failing that, I'm sorry, I don't know of any qualified service techs in your area but maybe another forum member can recommend one.

Lastly, no, spark plugs are not the fix, as you've discovered. Yes, it's safe to drive the car IN MANUAL MODE, until you resolve the issue.

Many C7 owner's have also had good results from using an AFM disabler (Range device). You must solve the original shudder problem first as an AFM disabler will only mask the problem at this point.

Best of luck
Ross
 

Attachments

I have the same issue on my 19 GS A8. In manual, no vibration, back to full auto and vibration felt in the seat. I did install a Range device which prevents the change to V4 mode. However, it the tranny issue does need to be addressed by dealer. Thanks cdnrx1 for the TSB - saves time in hunting it down. Did see recently that a class action against GM has started for the 8 speed tranny issues
 
Thanks so much - I found references to this online, but not the full TSB write up! It's exactly what is happening....now to find a shop I trust:confused:? I am surprised it hasn't been listed as a motor vehicle recall. Fingers crossed it gets solved....
Cheers
 
cdnrx1 said:
As you've already discovered, this is a well documented issue with the C7 as it relates to the 8L90 transmission. What you've described is the infamous "shudder" and, yes, it is related to the torque converter. The possible good news is that, from what you've described and based on your mileage, you may have caught it early in the development stage. Given that your vehicle is a 2016 it's most likely that the original ATF is the culprit and, as such, would be the most logical first step in solving the problem. However, there have been a number of component modifications and improvements relative to this problem. Valve modulator bodies, torque converters and, of course, ATF's, since the 2016 MY that have helped to improve the problem. I'd start with the ATF triple flush.

To test this theory, activate speed control at about 100 kph with the car in full auto, "D". Determine that it is shuddering. If yes, repeat the process in "M", manual mode. Does the shuddering stop? If yes then it's very likely that the problem is the ATF. If no then it's a different issue.

Just a few points of clarification on this issue. First off, the torque converter "shudder", as related to the 8L90 8 speed automatic transmission, is caused by the operation of the Active Fuel Management System (AFM). The problem occurs because the lock-up clutch in the torque converter fails to lock completely during the change from V8 to V4 mode. This is now thought to be due to excessive moisture absorption by the ATF, or so says the latest from GM. They have gone through 3 different formulations of Mobil 1 Synthetic ATF with the third, and so far final version, being the most successful. The general consensus is that the latest triple flush approach with the newest ATF (see attached TSB) will, in most cases, solve the problem.

As for the dealer not being familiar with this problem, not surprising. Try to talk to a senior service staff member or an experienced Corvette tech. Mention the triple flush for the 8L90 transmission and show them the TSB. Failing that, I'm sorry, I don't know of any qualified service techs in your area but maybe another forum member can recommend one.

Lastly, no, spark plugs are not the fix, as you've discovered. Yes, it's safe to drive the car IN MANUAL MODE, until you resolve the issue.

Many C7 owner's have also had good results from using an AFM disabler (Range device). You must solve the original shudder problem first as an AFM disabler will only mask the problem at this point.

Best of luck
Ross
Click to expand...
Have you experienced the shudder effect Ross?
 
Vanguard2001 said:
Have you experienced the shudder effect Ross?
Click to expand...
I have not experienced the shudder in my 2019 GS built in 04/18. The build date indicates that my car has the second formulation of the Mobil 1 Synthetic LV ATF HP, the "Black Label" fluid. The third, and so far final, version is the "Blue Label" fluid which is the one that seems to solve the problem as long as no actual torque converter damage has been done.

I started out using the Range device from day 1 and continued using it for that first driving season. Thing is that I drive 99% of the time in "M", manual mode. As such, AFM is never activated and the Range device, for me, was really redundant so I sold it. The other 1% is driven in full auto just to check for "shudder". So far, so good but I've only got about 19,000 kl's on the car. Fingers crossed, who knows what the future holds. :rolleyes:
 
Not much in Barrie, Georgian Chev... maybe, Paul Sadlon bigger maybe. You might need to go farther, Race Ready in Cambridge or Stingray Tech in Mississauga. I have used Peacock in Barrie, but I don't have a C7.
 
I'll chime in as I also went through the Tranny shudder..... 2017 Grand Sport, bought new. In 2020 I started to experience the shudder issue aorx 17000kms on it. After the tranny flush I did note some improvement but it returned within 3 mos. 2nd Tranny flush performed at that time and has not re-appeared since. Current mileage slighti over 26000kms. I drive 90% of the time in manual mode.
 
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Paul C7 said:
I'll chime in as I also went through the Tranny shudder..... 2017 Grand Sport, bought new in 2020 I started to experience the shudder issue aorx 17000kms on it. After the tranny flush I did note some improvement but it returned within 3 mos. 2nd Tranny flush performed at that time and has not re-appeared since. Current mileage slighti over 26000kms. I drive 90% of the time in manual mode.
Click to expand...
Which dealer did you go to for the ATF flush?
 
I presently have the vette booked at Paul Sadlon's for a diagnostic (@$125). I have driven it the last few days, strictly in manual mode to speeds up to 80Km/hr. No shudder, fingers crossed they diagnose it properly?!
In case anyone is interested....here's the pending Canadian Class Action Suit with Merchant Law. .... and the related article that includes the hotlink. Interesting read, if nothing else.....and yes, I did register with no obligation...
 
Paul C7 said:
I went to Dueck "Downtown" on 888 Terminal ave by Main St. As stated in my post I had it done twice, both under warranty. Hope it works out for you!
Click to expand...
Thanks I'll try going there later to see what happens. Any particular service person that is knowledgeable and how was their service overall?
 
No particular person, they were aware of the tranny issue. Lately, as they are closer to me, I have been using Eagle Ridge GM but found their service level and expertise to be lacking and will be returning to Dueck downtown.
 

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