2018 transmission shudder, lucky me
09-29-2018, 12:16 PM
#61
It's like riding a bike. You won't have any problems operating the manual transmission, and I predict you will be happy you got the stick shift every time you drive the car
09-30-2018, 07:29 PM
#62
Agreed, it's going to be easier now to drive one, rev matching, hill assist what more does one need? All these A8 threads, I just can't can commit to an auto it has to be a M7. I know the auto is convenient and faster but in my mind I would always be thinking will today be the day it fails? What fun is that? I am having a hard time understanding why people keep buying an A8 not just a C7 but across the GM line.
09-30-2018, 07:56 PM
#63
Race Director
it doesn't fail.. it's a fluid issue that's been resolved for over a year.. this trans has put C7's in the low 9's and street driven.. reliably... Once you get the new fluid (if miles are low enough) any issue is over with. and if not? you get a new converter NEW fluid and it's the same.
If you haven't driven an A8 equipped C7 (especially Z06 or SC C7) you have no idea what a great trans this is.. it's FANTASTIC..
If you haven't driven an A8 equipped C7 (especially Z06 or SC C7) you have no idea what a great trans this is.. it's FANTASTIC..
10-01-2018, 07:25 AM
#64
Burning Brakes
it doesn't fail.. it's a fluid issue that's been resolved for over a year.. this trans has put C7's in the low 9's and street driven.. reliably... Once you get the new fluid (if miles are low enough) any issue is over with. and if not? you get a new converter NEW fluid and it's the same.
If you haven't driven an A8 equipped C7 (especially Z06 or SC C7) you have no idea what a great trans this is.. it's FANTASTIC..
If you haven't driven an A8 equipped C7 (especially Z06 or SC C7) you have no idea what a great trans this is.. it's FANTASTIC..
10-01-2018, 07:34 AM
#65
Burning Brakes
Agreed, it's going to be easier now to drive one, rev matching, hill assist what more does one need? All these A8 threads, I just can't can commit to an auto it has to be a M7. I know the auto is convenient and faster but in my mind I would always be thinking will today be the day it fails? What fun is that? I am having a hard time understanding why people keep buying an A8 not just a C7 but across the GM line.
10-01-2018, 10:57 AM
#67
For some reason I could have sworn someone here has reported 19 with the problem too, but I might be wrong. I am not sure about timing but I believed people have had the flush, then TC changed just to have the same problem and have the TC changed again. Again not sure on the timeline of those in conjunction with the new fluid or I could have completely misread everything.....
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Jeffer (10-06-2018)
10-02-2018, 09:38 AM
#68
The difference is that when in V4, the A8 TC locks/unlocks every few microseconds or so to eliminate the vibration caused by running a V8 engine in V4 mode. This process is know as "pulse width modulation". By preventing the ECM/TCM from entering V4 mode, the Range stops this modulation of the TC lockup and lets it lock fully at the predetermined speed only to unlock when dropping below it.
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10-02-2018, 12:53 PM
#69
Le Mans Master
The shudder comes from the lockup clutch in the converter not "locking" in the manner expected because of increased wear from the constant on/off modulation it experiences during V4 operation. To a lesser extent these "micro-slips" of the friction clutch are used when engaging the lockup clutch in normal use but this is the same smooth engagement method GM has been using for many years and the wear from this portion of the operation is so minimal that the lockup clutch material will easily last through the normal lifespan of the transmission.
As the lockup clutch wears, it no longer grips as expected so the transmission controller commands greater lockup force which results in harsh engagement. When shudder starts your lockup clutch is in a cycle of constant greater slippage than expected followed by an abrupt harsh lockup as engagement pressure is ramped up to prevent the unexpected slippage and this constant dance of slip then hard lock that occurs during AFM operation creates shudder. The friction modified fluid GM now uses helps to mask some of the problem but the lockup clutch material in the torque converter is still being stressed under a severe duty cycle.
A lockup clutch was added to torque converters many years ago as a method to increase fuel economy by preventing the normal power loss that occurs in the converter at cruising speed and this also reduced heat buildup in the converter because the power lost in the converter gets converted to heat. It is very good at accomplishing its original intended purpose but not so much with the perverted AFM system GM uses. Just as the converter clutch slip is used to mask the additional vibration and harshness from operating a V8 as a V4 the new fluid is designed to mask the effects of utilizing a lockup clutch in a manner/duty cycle not originally intended. The problem could be addressed by either leaving the lockup clutch locked in AFM mode but then the vibration would be too noticeable to vehicle occupants OR just leave the clutch disengaged during AFM operation but then the very minimal mileage increase from V4 operation would probably turn into a mileage loss due to power lost in the open converter.
The best solutions so far are to either use a Range module or drive in manual mode or move to Europe because the A8 equipped Corvettes for that market only use AFM when eco mode is selected just like the M7 models sold in the U.S.
As the lockup clutch wears, it no longer grips as expected so the transmission controller commands greater lockup force which results in harsh engagement. When shudder starts your lockup clutch is in a cycle of constant greater slippage than expected followed by an abrupt harsh lockup as engagement pressure is ramped up to prevent the unexpected slippage and this constant dance of slip then hard lock that occurs during AFM operation creates shudder. The friction modified fluid GM now uses helps to mask some of the problem but the lockup clutch material in the torque converter is still being stressed under a severe duty cycle.
A lockup clutch was added to torque converters many years ago as a method to increase fuel economy by preventing the normal power loss that occurs in the converter at cruising speed and this also reduced heat buildup in the converter because the power lost in the converter gets converted to heat. It is very good at accomplishing its original intended purpose but not so much with the perverted AFM system GM uses. Just as the converter clutch slip is used to mask the additional vibration and harshness from operating a V8 as a V4 the new fluid is designed to mask the effects of utilizing a lockup clutch in a manner/duty cycle not originally intended. The problem could be addressed by either leaving the lockup clutch locked in AFM mode but then the vibration would be too noticeable to vehicle occupants OR just leave the clutch disengaged during AFM operation but then the very minimal mileage increase from V4 operation would probably turn into a mileage loss due to power lost in the open converter.
The best solutions so far are to either use a Range module or drive in manual mode or move to Europe because the A8 equipped Corvettes for that market only use AFM when eco mode is selected just like the M7 models sold in the U.S.
And your follow up reply about “The tick from the fuel pump is a slow tick at idle and sounds very much like a lifter tick since it is also driven via a camshaft lobe” was also enlightening. I had assumed the tick was a lifter tick. Now I know.
Thank you.
Last edited by Maxie2U; 10-02-2018 at 01:06 PM.
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Ericm1949 (10-06-2018)
10-02-2018, 01:14 PM
#70
Le Mans Master
10-02-2018, 01:26 PM
#71
Your post was completely enlightening. It helped me to finally understand about the issues associated with V4/V8 mode and and the lockup clutch in the converter.
And your follow up reply about “The tick from the fuel pump is a slow tick at idle and sounds very much like a lifter tick since it is also driven via a camshaft lobe” was also enlightening. I had assumed the tick was a lifter tick. Now I know.
Thank you.
You are very welcome. I believe with a Range module you will have very few worries about the A8 or any other AFM related issues.
I have been completely happy with the A8 in my 2016 Z06 and I have driven a lot of different manual and automatic equipped vehicles over the years. I also don't feel the need to go "evangelical religious" to try to convert every M7 driver to an A8 unlike some of the proselytizing M7 owners
10-02-2018, 01:34 PM
#72
I hear ya, I have about three discs in my lower back disintegrate and it's bone on bone now. On occasion, it flares up and using the left leg to push a clutch is not something I would look forward to so I can understand those scenarios would require an auto.
10-02-2018, 02:55 PM
#73
The Consigliere
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10-05-2018, 06:53 PM
#74
Le Mans Master
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2019 CHEVROLET SILVERADO PROPULSION LINEUP
4.3L V-6 w/AFM (6-spd.)2.7L I-4 Turbo w/AFM (8-spd.)
5.3L V-8 w/AFM (6-spd.)
5.3L V-8 w/DFM (8-spd.)
3.0L I-6 Turbo-Diesel (10-spd.)
6.2L V-8 w/DFM (10-spd.)
Last edited by NemesisC5; 10-05-2018 at 06:55 PM.
10-05-2018, 07:54 PM
#75
Just started in my 17 GS. All speeds, acceleration and deceleration as well during automatic down shifting. Jst under 7000 miled. Taking it to dealer tomorrow. They don't sell a lot of vettes so I hope they understand the problrm.
10-05-2018, 10:49 PM
#76
Race Director
Jist give them the tsb number
10-06-2018, 02:34 PM
#77
Update on last night's post. Got to dealer and spoke with one of their top men who also is the liaison to our local vette club. He attended last Tuesday's meeting which I did not. Apparently he made a short talk regarding this very problem and urged members with recent models to come in. He took me back to service who also was on top of the issue. She explained that they have not had good success with the flush solving the problem and GM requires that first. This dealer is writing it up in such a way that they will have me in only once and will do the flush and replace the torque converter at the same time. They are being very proactive in in addressing the iissue and taking good care of their customers and making the whole thing as easy as possible. Kudos to the dealership.
10-06-2018, 02:55 PM
#78
Le Mans Master
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St. Jude Donor '15-'16,'18
I wonder what GM will do if a car is flushed and then shudder returns past 5 years or 60k miles. Will they replace the TC at no cost?
10-06-2018, 03:10 PM
#79
Le Mans Master
10-06-2018, 03:26 PM
#80
Le Mans Master
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St. Jude Donor '15-'16,'18
Great way to sell extended warranties.