More A8 transmission problems
09-18-2018, 07:34 PM
#41
And the real problem is GM will flat out refuse to replace the transmission and people are still having issues with 2019s. So even the newer parts are still not performing as well as they should. I would suggest you take the car in and ave as many parts as possible updated in case you never had the TSBs done. They help some but not 100%.
09-18-2018, 09:23 PM
#42
Melting Slicks
09-19-2018, 09:54 AM
#43
I never use 7, it's useless. I have asked this before but no one has ever answered. Why would anyone buy an A8 knowing so many people have this TC issue? Mind boggling!
09-19-2018, 10:02 AM
#44
Burning Brakes
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Last edited by Sconn; 09-19-2018 at 10:03 AM.
09-19-2018, 11:02 AM
#45
Instructor
2016 Stingray,A8 2LT. I have over 13,000 miles on mine and I've never experienced the shudder, shift problems,or hard engagement from Park. However, I do acknowledge that the transmission is a bit Quirky compared to other automatics that I've owned. I've always assume It's the computer controlled components making their calculations, road conditions and other factors causing this Quirkiness.
09-19-2018, 11:23 AM
#46
Patman gets it, lol...
Let me explain myself. A 7 speed manual is not natural. It is not a perfect "H" configuration/pattern. With the M7, I'm afraid I will have to double check myself to see what gear I'm in, when I'm in gears 5-6. It's just counterintuitive - for me, lol...
The 6 speed manual has two "H" patterns. (HH). Reverse gear is either logically at the far lower right corner, or at the far upper left corner of the H pattern/configuration. The two "H" patterns are for gears 1-6.
That seventh gear is just odd!
It appears from what I've read that gears 5-7 are overdrive gears... If this is true, then why give me three OD gears? I could care less about MPG... This is not the car for gas consumption concerns...
I am/was fine with 4 speed, 5 speed and 6 speed manuals. M7 is just weird/unnatural for me.
Those who don't get it; we can agree to disagree, eh?
Cheers/Best,
BB
Let me explain myself. A 7 speed manual is not natural. It is not a perfect "H" configuration/pattern. With the M7, I'm afraid I will have to double check myself to see what gear I'm in, when I'm in gears 5-6. It's just counterintuitive - for me, lol...
The 6 speed manual has two "H" patterns. (HH). Reverse gear is either logically at the far lower right corner, or at the far upper left corner of the H pattern/configuration. The two "H" patterns are for gears 1-6.
That seventh gear is just odd!
It appears from what I've read that gears 5-7 are overdrive gears... If this is true, then why give me three OD gears? I could care less about MPG... This is not the car for gas consumption concerns...
I am/was fine with 4 speed, 5 speed and 6 speed manuals. M7 is just weird/unnatural for me.
Those who don't get it; we can agree to disagree, eh?
Cheers/Best,
BB
If you are a 1:1 max upper guy, then just use the "first H" and stop at 4th. The springs are set up to return the shifter to the middle anyway, so all will be well using 1-4 only.
09-19-2018, 12:30 PM
#47
Race Director
I understand all the rhetoric around the 8-speed transmission I have two of them one in my Sierra and my ZO6
the Sierra had to have the torque converter replaced at 25000 Miles because of the shudder and my Z06 is having the trans flushed now because it's developing a slight shudder at only 5800 miles.
There's nothing wrong with the transmission or the torque converter the problem is with the fluid viscosity
the new GM trans fluid for the 8-speed Transmissions is a low viscosity type
whoever decided to use the old formula really screwed GM and all of us over
they have figured out the problem and once you get the flush it cures most of the issues
some of the torque converter clutches are so beat up that even the flush with the new fluid didn't fix it hence the need for the new torque converter like my pickup.. if the vet needs one so be it thank God for the warranty and glad they fix the problem because before this it was just going to be a matter of everyone was beat forever
I spoke with a GM engineer at Carlisle in 2017 he told me they were changing the viscosity because of the issues and that would solve the problems so any Corvette or 8-speed made after a certain date probably late 17 or early 18 is my guess would have the new viscosity type in there.
and you know General Motors isn't about to announce we have this new fluid come in and get it changed I can't imagine how much it cost to do all that per car they're getting their butt kicked
the Sierra had to have the torque converter replaced at 25000 Miles because of the shudder and my Z06 is having the trans flushed now because it's developing a slight shudder at only 5800 miles.
There's nothing wrong with the transmission or the torque converter the problem is with the fluid viscosity
the new GM trans fluid for the 8-speed Transmissions is a low viscosity type
whoever decided to use the old formula really screwed GM and all of us over
they have figured out the problem and once you get the flush it cures most of the issues
some of the torque converter clutches are so beat up that even the flush with the new fluid didn't fix it hence the need for the new torque converter like my pickup.. if the vet needs one so be it thank God for the warranty and glad they fix the problem because before this it was just going to be a matter of everyone was beat forever
I spoke with a GM engineer at Carlisle in 2017 he told me they were changing the viscosity because of the issues and that would solve the problems so any Corvette or 8-speed made after a certain date probably late 17 or early 18 is my guess would have the new viscosity type in there.
and you know General Motors isn't about to announce we have this new fluid come in and get it changed I can't imagine how much it cost to do all that per car they're getting their butt kicked
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Rkovette (12-21-2019)
09-19-2018, 02:05 PM
#48
Get the M7. I had a 2015 A8 with both TC and stator problems and after 18 months of intrigue and hassle I moved to a 2017 GS M7. Life if good again. I also thought the M7 was one gear too many but after living with it for 18 months I can say that it is not confusing like I thought it might be, and most owners seem to agree.
Yes, if you are used to a standard 4 H pattern, anything else takes a little getting used to. I think the OD gears are great. In my Miata I longed for another higher OD gear when cruising. It just brings the RPM and noise level down considerably. The C7 also gets away with it because of all the torque (you've still got it in the OD gears unlike many other vehicles).
If you are a 1:1 max upper guy, then just use the "first H" and stop at 4th. The springs are set up to return the shifter to the middle anyway, so all will be well using 1-4 only.
If you are a 1:1 max upper guy, then just use the "first H" and stop at 4th. The springs are set up to return the shifter to the middle anyway, so all will be well using 1-4 only.
My head says get the Base Stingray, but my heart says, get the GS. Either way, M7 here I come.
Cheers/B
09-19-2018, 10:32 PM
#49
Burning Brakes
^^^ Yep; I plan to ignore gears 5-7, at least during break in... I have resigned myself to getting the M7. I'm sure I'll grow to love the M7. After all, it's just having to get used to something I'm not quite comfortable with - yet. I'll get over it. I'm now at the point of deciding, do I get the Base or a GS, lol... Have not made up my mind yet.
My head says get the Base Stingray, but my heart says, get the GS. Either way, M7 here I come.
Cheers/B
My head says get the Base Stingray, but my heart says, get the GS. Either way, M7 here I come.
Cheers/B
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BenDiem (09-20-2018)
09-20-2018, 07:25 AM
#52
Team Owner
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St. Jude Donor '15
"In honor of jpee"
Is it the trans alone, the engine alone, or a combo of both? Is it either their original design, or interface with each other? I have no idea, but there is a problem. And after 5 model years of the A8 and 6 for the AFM, it's not completely solved/fixed to my knowledge. Correct me if I'm wrong.
Considering the cost of engine repair, and auto trans repair/replacement, I would be hesitant to own the car with no warranty, whether it's the original powertrain or GM-sponsored extension that covers both components. Maybe that's an overly-cautious (and expensive) attitude, but I just have a big dislike for high-4 figure, mid-5-figure dollars spent for repairs. Especially if those potential costs can be worked around by an original warranty or its extension. Then again, many don't keep their cars that long in years or miles.
09-20-2018, 07:44 AM
#53
My 2016 Z06 A8 is fine but it has either been in manual mode or had a Range module installed since the moment I took delivery at the museum. The root cause of the major A8 issue is GM's ridiculous implementation of V4 mode where the torque converter lockup clutch is continuously modulated during V4 mode to attenuate the amount of engine vibration transferred through the rest of the powertrain. Lockup clutches (realistically no friction clutch) is going to stand up long term to this type of abuse where it is being engaged and disengaged multiple times per second. "Magic" fluid with friction modifiers can help reduce and to some extent mask the effects of wear from this operation but anyone who wants to keep their car long-term needs to seriously consider if they want to subject the transmission to this increased wear. GM MAY have addressed the increased oil consumption issues with their prior implementation of AFM but I don't plan to empirically test that premise either.
The only quirk I have with my A8 is in order to avoid an initial harsh 1 to 2 shift, while the car is still stationary after the first start of the day I shift to second and then back to first. The clutch pack associated with this range has a large fluid reservoir that is a little slow to initially fill after sitting overnight and this provides a good workaround to the initial harsh shift. GM may have updated the software to do a partial pre-fill of this clutch pack actuator so this step may not be needed with current production. The pre-fill strategy has been used on many other clutch to clutch architecture transmissions over the years and I have no idea why GM didn't do it in this case since it is under software control.
There is one relationship between the harsh initial shift and shudder. These clutch to clutch automatics depend upon very precise timing of the engaging and releasing clutch packs during shifts and this is accomplished via the controller working with precise sensors that measure input, output, and intermediate shaft speed. When unexpected slippage occurs (indicated via the RPM measurement of the various shafts) the transmission controller immediately responds by increasing apply pressure on the offending clutch pack(s). The initial 1 to 2 harshness occurs because of the slow fill resulting in an initial slip causing a command for an abrupt increase in apply pressure with resulting harsh engagement. Shudder occurs when there is unexpected slippage in the converter because the controller has ordered engagement of the lockup clutch. With shudder you have commanded engagement of the lockup clutch but because of wear there is slippage, when this happens apply pressure is abruptly increased resulting in harsh engagement. Under AFM in V4 mode this converter clutch slippage followed by abrupt lockup is happening continuously resulting in the shudder behavior. If the converter clutch were left completely unlocked during V4 mode operation then there would be no shudder but the already meager mileage gains from operating in 4 cylinder mode would be lost.
You will see the results of this increased wear before you begin to feel it as RPM variation at steady cruising speed will increase until it reaches the point where the controller is actively trying to combat this undesired slippage. By the time this occurs you already have experienced significant wear to the lockup clutch in the converter.
Shudder is very uncommon in the Z06 because it goes into V4 mode far less due to the different operating characteristics of its lower compression, forced induction motor. I suspect GM also made V4 mode engagement less aggressive with the Z06 because it doesn't have the vibration absorbing steel torque tube assembly or the AFM sound control valves which would have a very short life given the additional exhaust heat from the supercharged engine. In any case my Z06 will not be spending any time in V4 mode.
One other caution is that shudder can also come from engine problems and because the shudder problem is so common with an 8L90 (aka A8) transmission that engine operational/power delivery problems are going to be misdiagnosed because techs have become so used to the frequency of the issue with the 8L90 (and its 8L45 lower torque sibling).
The only quirk I have with my A8 is in order to avoid an initial harsh 1 to 2 shift, while the car is still stationary after the first start of the day I shift to second and then back to first. The clutch pack associated with this range has a large fluid reservoir that is a little slow to initially fill after sitting overnight and this provides a good workaround to the initial harsh shift. GM may have updated the software to do a partial pre-fill of this clutch pack actuator so this step may not be needed with current production. The pre-fill strategy has been used on many other clutch to clutch architecture transmissions over the years and I have no idea why GM didn't do it in this case since it is under software control.
There is one relationship between the harsh initial shift and shudder. These clutch to clutch automatics depend upon very precise timing of the engaging and releasing clutch packs during shifts and this is accomplished via the controller working with precise sensors that measure input, output, and intermediate shaft speed. When unexpected slippage occurs (indicated via the RPM measurement of the various shafts) the transmission controller immediately responds by increasing apply pressure on the offending clutch pack(s). The initial 1 to 2 harshness occurs because of the slow fill resulting in an initial slip causing a command for an abrupt increase in apply pressure with resulting harsh engagement. Shudder occurs when there is unexpected slippage in the converter because the controller has ordered engagement of the lockup clutch. With shudder you have commanded engagement of the lockup clutch but because of wear there is slippage, when this happens apply pressure is abruptly increased resulting in harsh engagement. Under AFM in V4 mode this converter clutch slippage followed by abrupt lockup is happening continuously resulting in the shudder behavior. If the converter clutch were left completely unlocked during V4 mode operation then there would be no shudder but the already meager mileage gains from operating in 4 cylinder mode would be lost.
You will see the results of this increased wear before you begin to feel it as RPM variation at steady cruising speed will increase until it reaches the point where the controller is actively trying to combat this undesired slippage. By the time this occurs you already have experienced significant wear to the lockup clutch in the converter.
Shudder is very uncommon in the Z06 because it goes into V4 mode far less due to the different operating characteristics of its lower compression, forced induction motor. I suspect GM also made V4 mode engagement less aggressive with the Z06 because it doesn't have the vibration absorbing steel torque tube assembly or the AFM sound control valves which would have a very short life given the additional exhaust heat from the supercharged engine. In any case my Z06 will not be spending any time in V4 mode.
One other caution is that shudder can also come from engine problems and because the shudder problem is so common with an 8L90 (aka A8) transmission that engine operational/power delivery problems are going to be misdiagnosed because techs have become so used to the frequency of the issue with the 8L90 (and its 8L45 lower torque sibling).
Last edited by NSC5; 09-20-2018 at 07:47 AM.
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09-20-2018, 09:02 AM
#54
My 2016 Z06 A8 is fine but it has either been in manual mode or had a Range module installed since the moment I took delivery at the museum. The root cause of the major A8 issue is GM's ridiculous implementation of V4 mode where the torque converter lockup clutch is continuously modulated during V4 mode to attenuate the amount of engine vibration transferred through the rest of the powertrain. Lockup clutches (realistically no friction clutch) is going to stand up long term to this type of abuse where it is being engaged and disengaged multiple times per second. "Magic" fluid with friction modifiers can help reduce and to some extent mask the effects of wear from this operation but anyone who wants to keep their car long-term needs to seriously consider if they want to subject the transmission to this increased wear. GM MAY have addressed the increased oil consumption issues with their prior implementation of AFM but I don't plan to empirically test that premise either.
The only quirk I have with my A8 is in order to avoid an initial harsh 1 to 2 shift, while the car is still stationary after the first start of the day I shift to second and then back to first. The clutch pack associated with this range has a large fluid reservoir that is a little slow to initially fill after sitting overnight and this provides a good workaround to the initial harsh shift. GM may have updated the software to do a partial pre-fill of this clutch pack actuator so this step may not be needed with current production. The pre-fill strategy has been used on many other clutch to clutch architecture transmissions over the years and I have no idea why GM didn't do it in this case since it is under software control.
There is one relationship between the harsh initial shift and shudder. These clutch to clutch automatics depend upon very precise timing of the engaging and releasing clutch packs during shifts and this is accomplished via the controller working with precise sensors that measure input, output, and intermediate shaft speed. When unexpected slippage occurs (indicated via the RPM measurement of the various shafts) the transmission controller immediately responds by increasing apply pressure on the offending clutch pack(s). The initial 1 to 2 harshness occurs because of the slow fill resulting in an initial slip causing a command for an abrupt increase in apply pressure with resulting harsh engagement. Shudder occurs when there is unexpected slippage in the converter because the controller has ordered engagement of the lockup clutch. With shudder you have commanded engagement of the lockup clutch but because of wear there is slippage, when this happens apply pressure is abruptly increased resulting in harsh engagement. Under AFM in V4 mode this converter clutch slippage followed by abrupt lockup is happening continuously resulting in the shudder behavior. If the converter clutch were left completely unlocked during V4 mode operation then there would be no shudder but the already meager mileage gains from operating in 4 cylinder mode would be lost.
You will see the results of this increased wear before you begin to feel it as RPM variation at steady cruising speed will increase until it reaches the point where the controller is actively trying to combat this undesired slippage. By the time this occurs you already have experienced significant wear to the lockup clutch in the converter.
Shudder is very uncommon in the Z06 because it goes into V4 mode far less due to the different operating characteristics of its lower compression, forced induction motor. I suspect GM also made V4 mode engagement less aggressive with the Z06 because it doesn't have the vibration absorbing steel torque tube assembly or the AFM sound control valves which would have a very short life given the additional exhaust heat from the supercharged engine. In any case my Z06 will not be spending any time in V4 mode.
One other caution is that shudder can also come from engine problems and because the shudder problem is so common with an 8L90 (aka A8) transmission that engine operational/power delivery problems are going to be misdiagnosed because techs have become so used to the frequency of the issue with the 8L90 (and its 8L45 lower torque sibling).
The only quirk I have with my A8 is in order to avoid an initial harsh 1 to 2 shift, while the car is still stationary after the first start of the day I shift to second and then back to first. The clutch pack associated with this range has a large fluid reservoir that is a little slow to initially fill after sitting overnight and this provides a good workaround to the initial harsh shift. GM may have updated the software to do a partial pre-fill of this clutch pack actuator so this step may not be needed with current production. The pre-fill strategy has been used on many other clutch to clutch architecture transmissions over the years and I have no idea why GM didn't do it in this case since it is under software control.
There is one relationship between the harsh initial shift and shudder. These clutch to clutch automatics depend upon very precise timing of the engaging and releasing clutch packs during shifts and this is accomplished via the controller working with precise sensors that measure input, output, and intermediate shaft speed. When unexpected slippage occurs (indicated via the RPM measurement of the various shafts) the transmission controller immediately responds by increasing apply pressure on the offending clutch pack(s). The initial 1 to 2 harshness occurs because of the slow fill resulting in an initial slip causing a command for an abrupt increase in apply pressure with resulting harsh engagement. Shudder occurs when there is unexpected slippage in the converter because the controller has ordered engagement of the lockup clutch. With shudder you have commanded engagement of the lockup clutch but because of wear there is slippage, when this happens apply pressure is abruptly increased resulting in harsh engagement. Under AFM in V4 mode this converter clutch slippage followed by abrupt lockup is happening continuously resulting in the shudder behavior. If the converter clutch were left completely unlocked during V4 mode operation then there would be no shudder but the already meager mileage gains from operating in 4 cylinder mode would be lost.
You will see the results of this increased wear before you begin to feel it as RPM variation at steady cruising speed will increase until it reaches the point where the controller is actively trying to combat this undesired slippage. By the time this occurs you already have experienced significant wear to the lockup clutch in the converter.
Shudder is very uncommon in the Z06 because it goes into V4 mode far less due to the different operating characteristics of its lower compression, forced induction motor. I suspect GM also made V4 mode engagement less aggressive with the Z06 because it doesn't have the vibration absorbing steel torque tube assembly or the AFM sound control valves which would have a very short life given the additional exhaust heat from the supercharged engine. In any case my Z06 will not be spending any time in V4 mode.
One other caution is that shudder can also come from engine problems and because the shudder problem is so common with an 8L90 (aka A8) transmission that engine operational/power delivery problems are going to be misdiagnosed because techs have become so used to the frequency of the issue with the 8L90 (and its 8L45 lower torque sibling).
Heidi
Save the Wave
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Yoggi (09-20-2018)
09-20-2018, 09:24 AM
#55
Safety Car
The first incident they were accommodating. They gave me a new loaner Silverado for over two weeks while everything was going on. But personally I think its the service manager who is the problem. He has had an attitude with me since I told him I wasn't going to pay for my armrest that was ordered while everything was still under warranty. It's not my fault that they failed to tell me that they ordered the part. But yes, after this incident I will most definitely not be going back, I'll be driving over an hour to a different dealership.
09-20-2018, 10:29 AM
#56
7th and 8th gear trans shudder
My 2017 Grand Sport has 4,500 miles on it. When driving in automatic (D) mode in 7th gear you get a quick shudder on and off. It also happens in 8th gear when cruising... When I drive in manual mode (M) in 7th 8th gear it doesn't do it. I've tested this several times. Anyone with any thoughts? Car Computer????
09-20-2018, 10:42 AM
#57
09-20-2018, 10:54 AM
#58
Melting Slicks
Member Since: Jul 2014
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A friend's 2015 3LT has the A8 trans issue and he's not heavy footed, but is pretty frantic w/ the gas and brake pedal operation even in a parking lots, taps brake and gas constantly which also brings on the lurches and clanks.
I'm guessing there are plenty of owners that only drive the car like a Blvd. cruiser and won't encounter these issues.
09-20-2018, 11:00 AM
#59
Much depends on how you drive the car. If you dive it like it's in a parade, easy starts and stops and just average speeds A8 will not display any issues. Mix some spirited driving, quick starts, some "heavy foot" action and then resume "parade" mode, the A8 will start to act up (mine does).
A friend's 2015 3LT has the A8 trans issue and he's not heavy footed, but is pretty frantic w/ the gas and brake pedal operation even in a parking lots, taps brake and gas constantly which also brings on the lurches and clanks.
I'm guessing there are plenty of owners that only drive the car like a Blvd. cruiser and won't encounter these issues.
A friend's 2015 3LT has the A8 trans issue and he's not heavy footed, but is pretty frantic w/ the gas and brake pedal operation even in a parking lots, taps brake and gas constantly which also brings on the lurches and clanks.
I'm guessing there are plenty of owners that only drive the car like a Blvd. cruiser and won't encounter these issues.
09-20-2018, 12:08 PM
#60
Instructor
I'm not an engineer or a physicist ,......However, If your Corvette already has forward momentum, The amount of effort the clutches needs to keep that forward momentum going is very minimal. When your Corvette switches from V8 TO V4 and vice versa there's very little wear happening anyway. This shuddering/chattering that's happening reminds me of my Harley Davidson big twin clutch,...…..It's a WET/DRY style clutch that can get oil on it and still function normally. It used to chatter too, Then I change the oil viscosity and haven't had a problem with it since! The V4 to V8 setup is designed to switch Literally millions of times during the life of the car. The GM people realize this and know that there won't be long term damage to the TC clutches. That's probably why they don't seemed too concerned about it and won't issue a recall for this problem JMHO.
My advice is to get the triple flush and see what happens. And try not to worry about long term damage.
My advice is to get the triple flush and see what happens. And try not to worry about long term damage.
Last edited by Chevette!?!?; 09-20-2018 at 12:23 PM. Reason: advice