A8 Transmission failure tracking
#961
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hanks10GS (03-02-2019)
#964
Pro
This is the first post from a thread on camaro6 titled TCC Shudder/ tuning solutions
"had the shudder start on my car last spring (MY16). I had the flush procedure done and for about 4 months it was resolved. Unfortunately the shudder has returned.
I noticed that if I command the TC to lockup manually (via HP Tuners) it goes to maximum pressure and it will not shudder at all. As of the most recent beta HP Tuners has added some additional TCC tables. I began doing some testing and for a few days now I have not had the shudder occur at all.
There are allowable slip tables per each gear relative to engine torque output. At low torque output GM allows up to 10 RPM of slip. This results in minimal pressure on the TCC apply. This is the design intent but because of whether it is a fluid friction modifier issue or a clutch material issue on the TC it allows the shudder to be felt.
I changed the table to allow 0 slip in 7th and 8th gear. This resulted in increased line pressure and the shudder does not occur. There is also a table that affects ramp rate of pressure based on slip but I did not need to touch that table.
I'm not saying don't go to the dealer and let them flush/replace the TC per the TSB but if you don't want to go that route it appears it can be mitigated via the TCM calibration.
I thought I'd share for the benefit of the community.
Tim"
"had the shudder start on my car last spring (MY16). I had the flush procedure done and for about 4 months it was resolved. Unfortunately the shudder has returned.
I noticed that if I command the TC to lockup manually (via HP Tuners) it goes to maximum pressure and it will not shudder at all. As of the most recent beta HP Tuners has added some additional TCC tables. I began doing some testing and for a few days now I have not had the shudder occur at all.
There are allowable slip tables per each gear relative to engine torque output. At low torque output GM allows up to 10 RPM of slip. This results in minimal pressure on the TCC apply. This is the design intent but because of whether it is a fluid friction modifier issue or a clutch material issue on the TC it allows the shudder to be felt.
I changed the table to allow 0 slip in 7th and 8th gear. This resulted in increased line pressure and the shudder does not occur. There is also a table that affects ramp rate of pressure based on slip but I did not need to touch that table.
I'm not saying don't go to the dealer and let them flush/replace the TC per the TSB but if you don't want to go that route it appears it can be mitigated via the TCM calibration.
I thought I'd share for the benefit of the community.
Tim"
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Ron_Attleboro_MA (02-11-2019)
#965
Team Owner
Member Since: Sep 2000
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St. Jude Donor '13
If GM finds out you've messed with the TCM tune, kiss the powertrain warranty good by.
And if there's anything on the car I really want to be covered by warranty, the A8 is number 1.
They probably wouldn't even do the new super flush procedure in the January bulletin, unless you're willing to pay ($400+?) for it.
It's well known that before approving major (expensive) work on an engine, GM requires the dealer to send them a readout of the tune history, they're very good at uncovering even "hidden" tunes. Whether they are doing that on transmissions, or will in the future, I don't know. But I don't want to be the test case.
And if there's anything on the car I really want to be covered by warranty, the A8 is number 1.
They probably wouldn't even do the new super flush procedure in the January bulletin, unless you're willing to pay ($400+?) for it.
It's well known that before approving major (expensive) work on an engine, GM requires the dealer to send them a readout of the tune history, they're very good at uncovering even "hidden" tunes. Whether they are doing that on transmissions, or will in the future, I don't know. But I don't want to be the test case.
#966
Pro
If GM finds out you've messed with the TCM tune, kiss the powertrain warranty good by.
And if there's anything on the car I really want to be covered by warranty, the A8 is number 1.
They probably wouldn't even do the new super flush procedure in the January bulletin, unless you're willing to pay ($400+?) for it.
It's well known that before approving major (expensive) work on an engine, GM requires the dealer to send them a readout of the tune history, they're very good at uncovering even "hidden" tunes. Whether they are doing that on transmissions, or will in the future, I don't know. But I don't want to be the test case.
And if there's anything on the car I really want to be covered by warranty, the A8 is number 1.
They probably wouldn't even do the new super flush procedure in the January bulletin, unless you're willing to pay ($400+?) for it.
It's well known that before approving major (expensive) work on an engine, GM requires the dealer to send them a readout of the tune history, they're very good at uncovering even "hidden" tunes. Whether they are doing that on transmissions, or will in the future, I don't know. But I don't want to be the test case.
#967
Instructor
My local dealer quoted me $870 for the new triple flush. I will probably just do it myself if I decide it needs to be done.
#968
Pro
yep mine quoted about the same. He did also mention that he was going to talk to the director as he doesn't think that the addition of the supercharger will void the trans warranty. Ill be amazed if that gets approved. but if not I'll likely change it out with some of the stuff from weapon x myself.
#969
Instructor
yep mine quoted about the same. He did also mention that he was going to talk to the director as he doesn't think that the addition of the supercharger will void the trans warranty. Ill be amazed if that gets approved. but if not I'll likely change it out with some of the stuff from weapon x myself.
#970
For those of you doing this on your own dime, I would hold off on the triple flush until this latest "fix" has been tested for a few thousand miles by those who have had it done under warranty. The claim was that the lower viscosity of the the prior recommended Mobil fluid would cure the shudder and now the current story is the hygroscopic tendencies of the low viscosity Mobil used as fluid fill #2 is responsible for exactly the same symptoms that was blamed on the viscosity of the original "HP" type fluid used when the 8L90 was introduced. I suspect when shudder reappears with the current magic fluid, the phase of the moon will be identified as the culprit.
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#971
For those of you doing this on your own dime, I would hold off on the triple flush until this latest "fix" has been tested for a few thousand miles by those who have had it done under warranty. The claim was that the lower viscosity of the the prior recommended Mobil fluid would cure the shudder and now the current story is the hygroscopic tendencies of the low viscosity Mobil used as fluid fill #2 is responsible for exactly the same symptoms that was blamed on the viscosity of the original "HP" type fluid used when the 8L90 was introduced. I suspect when shudder reappears with the current magic fluid, the phase of the moon will be identified as the culprit.
#972
I have to wonder if the trans fluid not reaching a normal operating temperature and "cooking" out the
absorbed moisture is a contributing factor in this ongoing issue. This time of year my trans barely reaches
100*F after an hour of driving and even in 100*F+ summer temperatures with spirited driving 135*F is
the most I have seen. From searching I have found a recommended minimum to be around 185*f, but I
don't see that happening for a street driven A8. I have also read that some A8's in other vehicles have a
thermostatically controlled valve that closes off the cooling loop until a minimum temp is reached. Why
wasn't this included on the C7 given its dual cooler system.
absorbed moisture is a contributing factor in this ongoing issue. This time of year my trans barely reaches
100*F after an hour of driving and even in 100*F+ summer temperatures with spirited driving 135*F is
the most I have seen. From searching I have found a recommended minimum to be around 185*f, but I
don't see that happening for a street driven A8. I have also read that some A8's in other vehicles have a
thermostatically controlled valve that closes off the cooling loop until a minimum temp is reached. Why
wasn't this included on the C7 given its dual cooler system.
#973
Burning Brakes
I found this article (see attached) on the GM Techlink website. It explains that the old fluid would absorb moisture over time but the new fluid should not.
John
John
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#974
I find it interesting that "normal" Mobil 1 synthetic ATF along with numerous other transmission fluids that meet the specs of various GM (and other manufacturer) transmissions don't have a shudder issue EXCEPT when used in the 8L45/8L90 applications. Transmission fluid additive packs have made common ATF somewhat hygroscopic since the late 1970s so it isn't like the original Dexron HP (the original fluid for the 8L90) suddenly brought about a hygroscopic issue to ATF.
So we started with the original "special" spec beyond then current Dex VI which was named Dexron HP for use in the 8L series transmissions. Next we get Mobil 1 "black label" low viscosity synthetic to replace the original HP spec fluid. Now that has been replaced by the "blue label" version that is more resistant to hygroscopic induced shudder.
Unless forced to in court, GM isn't likely to divulge why the 8L series is so problematic with respect to torque converter lockup clutch shudder nor how these new fluid specs which have changed significantly from the original specs around which the 8L90 was designed will impact future operation including longevity.
So we started with the original "special" spec beyond then current Dex VI which was named Dexron HP for use in the 8L series transmissions. Next we get Mobil 1 "black label" low viscosity synthetic to replace the original HP spec fluid. Now that has been replaced by the "blue label" version that is more resistant to hygroscopic induced shudder.
Unless forced to in court, GM isn't likely to divulge why the 8L series is so problematic with respect to torque converter lockup clutch shudder nor how these new fluid specs which have changed significantly from the original specs around which the 8L90 was designed will impact future operation including longevity.
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1950silverstreak (02-09-2019)
#975
Burning Brakes
Thanks, Range - AFM Disabler
Someone on StringRayForum had a problem:
https://www.stingrayforums.com/forum...-problems.html
Has anyone done research that disabling does not harm?
#977
I just picked up a 2015 corvette a8 transmission
I just picked up a 2015 and left the dealer ship and I felt shuttering. Ya think before selling they would fix this problem. I noticed if I put it in the sport mode it drove fine. Now I need to take it back to figure out what this is..
#978
Burning Brakes
A update on my car, I had the NEW flush done a few weeks ago and the car still runs fine, the shudder is gone. Hopefully it stays that way, time will tell.
John
John
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joemessman (02-12-2019)
#979
Le Mans Master
Member Since: Nov 2015
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Why didn't you drive it before you bought it?