The following is my understanding of the issue, anyone with more in-depth information please feel free to correct me or augment it.
Quote:
Originally Posted by JT58
What is the difference between the 8 speed and the 10 speed? Is the 8 speed totally different, developed just by GM and the 10 speed completely new developed by Ford and GM?
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The 10-speed longitudinal transmission was designed by Ford.
GM's high torque 10L90 application of this transmission design has different programming and much improved torque capacity over both Ford's 10R80 and GM's lower end 10L80. It is only used in the ZL1 and the 2019+ Cadillac CT6, while the 2019+ SS uses the 10L80.
As part of the the collaboration, GM designed a 9-speed transverse unit that Ford later rejected.
(
source; I'm finding the same information everywhere).
Quote:
Originally Posted by JT58
Did GM do anything to address the shudder in the current 8 speeds? I believe it was a fluid issue that fried the torque converters? Someone on a previous post stated that it was a programming issue? Was it an issue 2016-2018 models only? I am so afraid of the 8 speed as it is the sole reason I ditched my 2017 Camaro RS and now drive a 2016 with M6.
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The "shudder" seems to be addressed completely by the Jan 2019 fluid (Mobil 1 Synthetic LV ATF HP, part number 19417577). If it is performed on a vehicle that was exposed to shudder too long, the torque converter may be damaged in that too much friction material may be abraded from clutch packs, and in these cases the torque converter needs to be replaced (see also
this link).
I have not seen reports either here or from my dealership of the shudder returning after a flush + TC replacement.
The programming issue is that GM's transmission (TCM) programming logic allows a relatively significant amount of slip in 7th and 8th gears for better daily drivability, which, coupled with the overly hygroscopic old fluids, accelerates the burnishing of clutches. As far as I understand, the shudder itself is originating from an alternating pattern of low and high pressure pump application during slip.
Several members here have had their TCM's reprogrammed to reduce or remove the allowed slip altogether (by "zeroing out the slip tables"), which eliminates the symptoms unless the torque converter is damaged beyond hope. Also, the factory transmission tune has a large safety margin in terms of torque management and shift times that can be improved with a custom tune.
On the other hand, apart from the shudder concern the 8L90 is a very powerful and stout transmission with high torque capacity, and it performs extremely well in standard as well as high power applications after a tune. Since there is an apparently working fix for the shudder condition, the risk associated with getting the 8L90 is much lower than initially.
As to myself, I am on the latest fluid with a proper transmission tune, and have zero problems with the A8, it's smooth during low power daily driving and an animal at WOT and in performance shift mode, pulling perfectly timed upshifts and downshifts with no jerking, rev hangs or shudder.