ATF SolvesGM Transmission Shudder Issues?

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Hi All, May have been discussed - Short story - many GM transmissions are apparently afflicted by a shudder with wavering RPM, clunking, etc - 2016-2018 so far. GM reportedly changed the fluid requirement a year ago, then when that didn't solve the problem, they started replacing torque converters. But, they started getting returns on the torque converters. In late 2018 they started shipping a new transmission fluid that would reportedly fix the issue ... just had mine replaced on a 2017 Silverado that was exhibiting the issues. Initially, seems to have fixed issues on mine. Part number is: 19417577 Anyone have engineering or insider insight on the fluid, sourcing (assuming it is Mobil syn of some sort)? Thanks.

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The TSB & new fluid are being discussed on many GM forums...as you've surmised it is a "new formula of Mobil 1 Synthetic LV ATF HP transmission fluid" to address the lingering shudder issues with the 8L45 & 8L90.
 
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Originally Posted by stephenson
Short story - many GM transmissions are apparently afflicted by a shudder
Scope of the issue is limited to 8L45 and 8L90 transmissions.
Originally Posted by stephenson
Part number is: 19417577 Anyone have engineering or insider insight on the fluid, sourcing (assuming it is Mobil syn of some sort)?
19417577 is Mobil 1 LV ATF HP https://www.mobil.com/English-US/Passenger-Vehicle-Lube/pds/GLXXMobil-1-Sythetic-LV-ATF-HP?p=1 It is really nothing more than a high quality Dexron HP ATF, which is what the 8Lxx transmission have always spec'd.
 
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The wording in the GM Tech Center bulletin specifically states "new formula". That plus a new P/N suggests Mobil tweaked the add pack (e.g. friction modifiers) to deal with shudder.
 

stephenson

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Thanks ... if this solves the problems, it is really a tour de force of how the various engineering regimes can work together to solve what seemed initially as an intractable problem! Hoping for the best!
 
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Originally Posted by clinebarger
Constant converter clutch slip shearing the ATF, This has been an issue for 20 years now & got magnified by the implement of AFM. The question is.....How long will this "fix" last?
Until you have to change the fluid again
 
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Originally Posted by clinebarger
Constant converter clutch slip shearing the ATF, This has been an issue for 20 years now & got magnified by the implement of AFM. The question is.....How long will this "fix" last?
Maybe it is just me, but when a fluid the is "the fix" for a problem it scares me.
 
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This exact issue is slowing me down from buying 2014 or newer C7 Corvette. These GM vehicles have been plagued with A8 transmission problems and nothing seems to be a permanent fix. As the vehicles attain higher mileage they get worse from what I have read. There is a plug and play device called a RANGE which is supposed to eliminate the engine from going from 8 cylinders to 4. This RANGE device is supposed to help the problem somewhat or keep it from getting worse. It seems to me from what I have read GM is still trying to fix this problem and it is not working. The 2013 and older Corvettes didn't have this problem. I have a buddy of mine who had a new Suburban a couple years ago and he replaced 3 transmissions. GM knows they have a problem and part of the cure is drive it with extreme care but who wants to own a Corvette or any automatic and not nail it through the gears once in a while?
 
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Might be worth finding a fluid that holds up to shear the best until a real fix comes along.
 
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2 years ago I performed an exchange with maxlife multi-vehicle compatible Dex - VI in my 4l65e. Started shuddering almost immediately. After some investigation thanks to this site found out that maxlife multi-vehicle is thinner then the GM Dex VI spec. So I beefed it up with some Lucas transmission fix which is basically a thickener. Shudder went away as fast as it showed up. So I think it's the fluid and they are swapping torque converters that are better compatible with the thinner than DexVI Dex-HD. I'm guessing that a thicker fluid would probably solve it.
 
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Originally Posted by XL1200RFan
The wording in the GM Tech Center bulletin specifically states "new formula". That plus a new P/N suggests Mobil tweaked the add pack (e.g. friction modifiers) to deal with shudder.
According to Al Oppenheiser and team on the 8spd in the Camaro
Quote
If a car that is experiencing shudder is not serviced early, the torque converter clutch material could become burnished and may require a torque converter replacement. The dealer has a specific service procedure that they will follow to determine the required service for your vehicle. So, if you believe you are experiencing shudder, see your Chevy dealer right away, because the earlier you get it serviced, the better. Please keep in mind, not all 8-Speed Automatic Transmissions exhibit this issue. So, what is the service procedure? Once we determined the issue was due to the quality of the friction modifier in the fluid, we developed a service procedure to flush and fill the transmission fluid 3 times, which eliminates most of the shudder concerns. This service process may not work for a vehicle with shudder that goes too long without service, in which case it will most likely require a new torque converter. Since we started using Dexron HP transmission fluid in March of 2017 both in production and for service, we believe we have basically eliminated the shudder. When used for service, it only requires a single flush and fill.
 
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stephenson

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Oppenheimer may be talking to a previous procedure ... I can't find 18-NA-355, but I believe they used a flushing procedure vice three separate drain and fills. In any case, after 240 miles of mixed driving yesterday, I had zero shudder. Also, the usual clunks during light throttle up shifts and downshifts also almost completely gone.
 
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According to GM, the problem was the fluid being hygroscopic, so much so that the fluid would not give up the water even when hot. The accumulated water in the fluid affected the friction of the fluid and created the shudder especially when the engine was operating in V4 mode which has built in TCC slip of around 10 rpm to reduce felt engine vibration in V4. Unfortunately the wet fluid created the shudder. The new fluid is supposed to fix the issue. The TSB 18-NA-355 is new as is the fluid and change procedure which varies depending on the vehicle. Initially the fluid is in short supply, and is being rationed to areas of the country that had the most problem. Humid states in the South and South East. It should be country wide by Feb/March The TSB is available online but for a $15 fee. Im sure it will become available on the no charge sites soon enough.
 
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MolaKule

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I guess my question would be, if moisture ingress is the problem, where is the moisture coming from? If these transmissions have a dipstick, then the dipstick seal must be allowing air to bypass it and suck in moisture when the fluid cools.
 
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I don't know about these new trannies, but the GM 4-speed boxes had vents. I suppose if one somehow made a radically hygroscopic fluid that can apparently hold onto water even at temp where it should be vaporizing, then it is possible.
 
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The real fix is to get a tune that uses lock or unlock on the tq converter. Every since GM starting slipping the converters there have been more problems. (may also require hard parts on trans)
 
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