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New bulletin was JUST released by GM. It should make it to the dealers soon, if it hasn't already, in addition to the new Mobil 1 ATF formula. I heard some dealers are already getting the new Mobil 1 ATF formula as we speak.

The New GM TSB number is: 18-NA-355.
 

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2013 CTS-V A6 Black Diamond Sedan
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78 Posts
Re: New GM TSB 18-NA-355 to address transmission shutter has been released...

Do you have copy of the TSB?
 

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It does not appear on any of the searchable TSB databases I can access nor does the number appear on any of the other fora that have cars using the 8L90 transmission.
 

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So far noone has been able to actually produce this TSB. I am not saying it is a bad number, but across this forum and the Corvette forum, everybody searching their sources has come up empty on this 18-NA-355 TSB.
 

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2017 CTS V Crystal White with carbon black
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370 Posts
Do any of you guys have that shudder and need this fix? I'm not familiar with it. Are our cars filled with Dexron from the factory?

Richard
 

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2016 CTS-V Stellar Black Sedan & 2016 ZO6 Corvette
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119 Posts
Dealer replaced my torque converter at 7,000 miles (car was about 9 months old) and problem cured. Now at 27,000 miles, it is back. Dealer is waiting for info for GM to resolve issue.
 

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2009 CTS-V , 2011 CTS-V Coupe, 2012 CTS-V Sedan, 2016 CTS-V
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283 Posts
My 2016 V is doing now, just went to Daytona and back had the dreaded rumble/vibration through the whole car when in V-4 mode with cruise control set at 78 mph. Thought it was just the worn out road surface, transmission has a pulsating vibrating every 3-5 seconds while at speed and in V-4 mode until it would automatically shift back to V-8 mode. Need to get my intel from you guys then make appointment with dealership to get this fixed.
 

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I had my 2016 Corvette at the dealer yesterday for the 8 speed shudder problem. They did the new flush with the new style fluid and it runs fine now. I asked for a copy of TSB # 18-NA-355 and it is 29 pages as it covers many cars. The problem is I scanned the file and it is about 8 MB and I cannot post a file bigger then 1.5MB to this website. I had the same problem at Corvette Forum but they let me post a file up to 5MB so I just broke it down into two files. Anyone have a easy solution? I can email it if you want, just post or send me a PM.

John
 

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Hi John. My local GM dealer recently (1/24/19) diagnosed my 2016 Camaro SS with the same code as your Corvette (18-NA-355). I google searched it and found your post. They flushed and changed my transmission oil (13K miles) and the shudder has greatly improved. However, I am noticing some new hesitations as the transmission shifts in lower gears. I am very interested in reading through the bulletin if you wouldn’t mind emailing it to me. My email is [email protected]. Thank you so much!
 

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Hi John. My local GM dealer recently (1/24/19) diagnosed my 2016 Camaro SS with the same code as your Corvette (18-NA-355). I google searched it and found your post. They flushed and changed my transmission oil (13K miles) and the shudder has greatly improved. However, I am noticing some new hesitations as the transmission shifts in lower gears. I am very interested in reading through the bulletin if you wouldn’t mind emailing it to me. My email is [email protected]. Thank you so much!
I just emailed it to you Maureen.

John
 

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2016 CTS-V
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308 Posts
I had that TSB done just last week.
Shifting was harsh and the shudder was very present.
drove home, drive perfectly normal. no more harsh shifting, no shudder even when I tried to replicate it.
so, so far so good.
I hope it lasts!

EDIT:
I should add that I no longer have a 2009 V. I have a 2016 V3
 

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2016 CTS-V Stellar Black Sedan & 2016 ZO6 Corvette
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My 2016 CTS-V, 23,000 miles, was at the dealer's shop yesterday for the lubricant change....wife drove the car home and says it is now fine...no shudder. The original torque converter was replaced at 7,000 miles to cure the shudder then as the lubricant change didn't make any difference. My 2016 ZO6 (27,000 miles) had the fluid change done at 12,000 miles and so far it is still ok. Keeping my fingers crossed.
 
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