gm tsb 18-na-355 transmission flush

cstmg8 · August 14, 2020

Has anyone recently had this done successfully to eliminate the shudder? I read in another thread that GM no longer wanted to honor it, because of the class action results.

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rav3 · August 14, 2020

8 minutes ago, cstmg8 said:

Has anyone recently had this done successfully to eliminate the shudder? I read in another thread that GM no longer wanted to honor it, because of the class action results.

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Correct me if I'm wrong, but isn't this just for the 8 speed transmission?

https://static.nhtsa.gov/odi/tsbs/2019/MC-10163890-9999.pdf

reardiff · August 14, 2020

Been curious about this myself. I have a 2017 with similar symptoms, fairly minor compared to what some others have posted about on here but can tell it's there. Been to two different dealers and neither want to do anything about it saying 'normal' along with the occasional clunks and hard down shifts. My 3 year warranty expires in two weeks so guessing anything under warranty won't happen at this point.

What's the difference between the flush process outlined in the TSB vs a regular transmission flush the dealer would perform for routine maintenance? I'm just over 30k miles and thinking it may be good time to just do a flush but this actually solve anything or is there a specials procedure that needs done?

GrumpyAeroGuy · August 14, 2020

Had the flush done (under warranty) 2 weeks ago to eliminate shudder on-set. 8sp/2016/51000mi.

Eliminated it completely. In fact, I would say the transmission is very much improved overall.

Fixed it for me.

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LDM · August 14, 2020

Had this done a few months ago on my truck, although my issue was not the shudder but the really hard 1-2 shifting when cold. Fixed it immediately and have not had the issue since. If you have the 8L90E, you should definitely have it done to get the new fluid, the older fluid would absorb water easier, which is supposedly the cause of most of the issues with the transmission.

newdude · August 14, 2020

1 hour ago, cstmg8 said:

Has anyone recently had this done successfully to eliminate the shudder? I read in another thread that GM no longer wanted to honor it, because of the class action results.

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We just did a 2019 Colorado for it under warranty, no issues. The flush procedure can be done under powertrain warranty, which is 5yr/60k on 2016 and newer.

43 minutes ago, reardiff said:

Been curious about this myself. I have a 2017 with similar symptoms, fairly minor compared to what some others have posted about on here but can tell it's there. Been to two different dealers and neither want to do anything about it saying 'normal' along with the occasional clunks and hard down shifts. My 3 year warranty expires in two weeks so guessing anything under warranty won't happen at this point.

What's the difference between the flush process outlined in the TSB vs a regular transmission flush the dealer would perform for routine maintenance? I'm just over 30k miles and thinking it may be good time to just do a flush but this actually solve anything or is there a specials procedure that needs done?

Dealer aftermarket flush equipment is a no-no on any transmission (BG, Castle, etc.). The procedure used for the 8 speed is really more of a drain and fill type flush, and not a power flush like a flush machine. They install a drain hose to the transmission cooler fitting port, pump out 4 quarts, add 4 quarts, pump out 4 more, add 4 more. The dealer uses the approved fill tool, which was their cooler flow machine repurposed to use only the new fluid to fill the transmission. A total of 20 quarts is used for the procedure.

especter · August 14, 2020

I just had the dealership perform the transmission service on my 2019 Sierra 1500 5.3L 8-speed. Service was performed on Tuesday.

Parts included: BG 6600 Transmission Flush kit ($47, includes 106BG & 310BG), Filter (GM Part No. 24274402), and Fluid (GM Part No. 88865601)

Issues thus far:

Last night I noticed an oil spot in my driveway, put some cardboard under the transmission pan, and drove it to the dealership this morning. They confirmed the pan was "seeping" and blamed it on a defective gasket.

Looking at the parts list, they used the AC delco ATF. Should they be using the Mobile 1 Synthetic LV fluid per the 18-NA-355 bulletin??

Any help would be appreciated, because I'm about to blow my gasket..........

especter · August 14, 2020

I also had to give them a copy of this bulletin....because it looks like they did a flush instead of following the attached bulletin. I know I'm posting this in the wrong thread (I have a new platform truck).

MC-10163241-9999.pdf

cstmg8 · August 14, 2020

Correct me if I'm wrong, but isn't this just for the 8 speed transmission?
https://static.nhtsa.gov/odi/tsbs/2019/MC-10163890-9999.pdf

I have the 8 speed

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Colossus · August 15, 2020

12 hours ago, newdude said:

Dealer aftermarket flush equipment is a no-no on any transmission (BG, Castle, etc.). The procedure used for the 8 speed is really more of a drain and fill type flush, and not a power flush like a flush machine. They install a drain hose to the transmission cooler fitting port, pump out 4 quarts, add 4 quarts, pump out 4 more, add 4 more. The dealer uses the approved fill tool, which was their cooler flow machine repurposed to use only the new fluid to fill the transmission. A total of 20 quarts is used for the procedure.

The flush machines use the transmission pump to do the flushing. Including the BG flush machine. It is tested and true and it works fine.

M1ck3y · August 16, 2020

I was under the impression gm doesnt do any work on the 8spd anymore unless its failed. Thanks to the class action lawsuit being thrown out. Also under the impression that the new fluid will eventually make the transmission problems worse after a certain amount of time. Is this wrong? Id like to have it done to my truck if it actually works.

especter · August 16, 2020

11 hours ago, M1ck3y said:

I was under the impression gm doesnt do any work on the 8spd anymore unless its failed. Thanks to the class action lawsuit being thrown out. Also under the impression that the new fluid will eventually make the transmission problems worse after a certain amount of time. Is this wrong? Id like to have it done to my truck if it actually works.

I don’t see why they would decline transmission service if it is under warranty or if it is preventative maintenance on the 8 speed transmission (especially considering new trucks are still getting the 8 speed). If the educated consumer is aware that transmission fluid exchange (drain/ fill, filter & gasket replacement) is recommended at 30K intervals, they should honor the request.

The filter replacement is not part of their procedure and needs to be requested.

Monitor for leaks after the work has been performed, because the mechanic may have over-torqued the transmission pan bolts, which could lead to a failed gasket & leak.

If you come to them with a 100,000+ mile car or with transmission issues (which has not had regular service transmission service), I wouldn’t be surprised if they decline or recommend against the service. Otherwise, they may be held liable for a transmission failure after it has been serviced.

I would just make it clear that you’re not interested in paying for the flush & specifically want the 20 quart fluid exchange with the ATF machine (without the use of aftermarket flush or additives). The shop foreman and mechanics are trained on the issues with these transmissions and should closely follow the prescribed service procedures or service bulletins. The service writers on the other hand may not be aware & so when scheduling the work the request needs to made clear and documented in the write up. Furthermore, I had to request the Mobil 1 synthetic ATF HP fluid (blue label), as they don’t stock it.

This is my opinion.

ImHowl · August 17, 2020

I have a 2018 with the 6.2l and 8 speed. I had the shudder issue pretty bad. Mine was mostly the "rumble strip" experience. If I was driving at a steady speed the transmission would "load" like it was going to shift up, then never shift, which would cause the truck to feel as if it was driving over a rumble strip. It did this every minute or so. It was terribly worse when towing. Would make the truck shake pretty good.

I had the service done with 22621 on the odo on Jan 21 2020 and it worked like a champ. I have ZERO issues now. It was covered under warranty, so I paid $0 for this to be done.

100% worth it in my opinion.

Edited August 17, 2020 by ImHowl

fsuguy92 · August 17, 2020

Took mine to the dealer and they didn't even acknowledge that the TSB existed.

M1ck3y · August 18, 2020

Yeah, I was hoping a gm tech would chime in. Because Ive seen a gm tsb stating all 8spd tsbs are void and not to perform any work on them without gm authorization.