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Just found a Tech Link for the 8 speed, that may help explain the complaints that many have about harsh or slipping shifts, that GM has told customers that all this is normal. Read and see if this is any help.

 

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Just found a Tech Link for the 8 speed, that may help explain the complaints that many have about harsh or slipping shifts, that GM has told customers that all this is normal. Read and see if this is any help.

Wow super helpful article on determining the fact that this feels like and is, a pos transmission that won't likely stand up to the test of time.

Sent from my SM-G975U using Tapatalk
 

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I just got my truck back from the dealer. They did the 18 NA 355, which is the fluid flush. Wow , what a difference. The truck feels like brand new again. Shifts are smooth and fast. I don't have that first harsh down shift clunk while coming to a stop. The shudder is gone. I had 20,080 miles on my 2018 Z71. I never would have believed the fluid would have this effect on shift and the shudder.
 

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Just found a Tech Link for the 8 speed, that may help explain the complaints that many have about harsh or slipping shifts, that GM has told customers that all this is normal. Read and see if this is any help.

Just saw this thread while researching for my arbitration hearing. Thanks for posting. One thing that jumped out to me was:

The transmission adapts can be reset and relearned on most vehicles. Clearing and relearning the shift adapts should not be considered a repair process and is intended to be performed only when a repair has been performed to the transmission.
The first time I brought it in for the harsh shifting, this is all they did, they didn't do a single repair, kept my truck for 3 weeks, and only cleared the shift adapts. Per GM, that's not a repair. Hopefully that helps my case.
 

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Just saw this thread while researching for my arbitration hearing. Thanks for posting. One thing that jumped out to me was:



The first time I brought it in for the harsh shifting, this is all they did, they didn't do a single repair, kept my truck for 3 weeks, and only cleared the shift adapts. Per GM, that's not a repair. Hopefully that helps my case.
I don't know how it is on the MDI but I know on the tech II it actually gives a warning for shift relearns on the 4 speeds that it is only to be performed if work is done to the transmission. Nothing about adaptive shifting is new, the old trucks used it too it just wasn't as intrusive because fuel economy wasn't its goal. Learning driving habits was.
 

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this 8 speed and all its pressure regulation devices loves fresh fluid.
Most guys who do a fluid change notice immediate improvement.
Also, driving habits may be an issue. Being more aggressive on the pedal can help the shift learn dial in. I actually think my Pedal Commander used during my first 20K helped my learn because Im typically very light on the throttle. I don't use the PC now and the truck drives smooth.
Knock on wood...
 

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I just got my truck back from the dealer. They did the 18 NA 355, which is the fluid flush. Wow , what a difference. The truck feels like brand new again. Shifts are smooth and fast. I don't have that first harsh down shift clunk while coming to a stop. The shudder is gone. I had 20,080 miles on my 2018 Z71. I never would have believed the fluid would have this effect on shift and the shudder.
are they just putting in a certain type of fluid? is that something someone can do without taking it to the dealer? I haven't researched too much on the shudder issue so not really sure what they are replacing fluid-wise or the like.
 

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They switched from a "black label" Mobil 1 fluid to a "blue label" Mobil 1 fluid. Details here: TCC Shudder and New Mobil 1 Fluid Exchange – TechLink

I bought my '17 used with 14k on it this past May. It had no shudder when I test drove it, but by the end of June it did. We took a vacation in July and I had the flush done when we got home. No issues since; however, I recently did the heated steering wheel upgrade and pulled the negative battery cable while working with the airbag, and since then (about a month so far), the truck has far fewer harsh 1-2 and 2-1 shifts when cold. The learning thing seems to be real. Who knows how the previous owner drove; I'm pretty light-footed myself.
 

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Per the article, the older fluid is hydroscopic. The trans may be "sealed" but it has a vent. I bet the issues with shudder are more prevalent in moist/humid environments.

A buddy has a new ZR2 and it shifts perfectly as does my Canyon's 6 speed, but Colorado where we live is one of the dryer places on the planet. Coming up on changing my truck's tranny fluid and wanting to use Mobil 1 Synthetic, but the article said the black label stuff is for the 8 speeds?
 

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They switched from a "black label" Mobil 1 fluid to a "blue label" Mobil 1 fluid. Details here: TCC Shudder and New Mobil 1 Fluid Exchange – TechLink

I bought my '17 used with 14k on it this past May. It had no shudder when I test drove it, but by the end of June it did. We took a vacation in July and I had the flush done when we got home. No issues since; however, I recently did the heated steering wheel upgrade and pulled the negative battery cable while working with the airbag, and since then (about a month so far), the truck has far fewer harsh 1-2 and 2-1 shifts when cold. The learning thing seems to be real. Who knows how the previous owner drove; I'm pretty light-footed myself.
There are some ECM parameters that affect shifting, so those may be the cause, but a simple battery disconnect does not clear the learned TCM cells. The TCM is protected, and only a TECH II scanner can be used to clear them, hence the warnings it gives before a relearn procedure is started. It is this way on the 6spd too.
 

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Per the article, the older fluid is hydroscopic. The trans may be "sealed" but it has a vent. I bet the issues with shudder are more prevalent in moist/humid environments.

A buddy has a new ZR2 and it shifts perfectly as does my Canyon's 6 speed, but Colorado where we live is one of the dryer places on the planet. Coming up on changing my truck's tranny fluid and wanting to use Mobil 1 Synthetic, but the article said the black label stuff is for the 8 speeds?
My 1st event happened at 11K(black label flush), here in south FL, and 2nd at 24K, before getting the blue label stuff. I went quite a ways further than we commonly see here, driving in this sauna. Wife's truck started at 6K, but that was 1.5 yrs in for her 4 mile daily commute, and me opening it up on the weekends to blow it out.
 

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There are some ECM parameters that affect shifting, so those may be the cause, but a simple battery disconnect does not clear the learned TCM cells. The TCM is protected, and only a TECH II scanner can be used to clear them, hence the warnings it gives before a relearn procedure is started. It is this way on the 6spd too.
You need the MDI. I have a TECH 2 and the twins aren't supported. I've tried lol.
 

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There are some ECM parameters that affect shifting, so those may be the cause, but a simple battery disconnect does not clear the learned TCM cells. The TCM is protected, and only a TECH II scanner can be used to clear them, hence the warnings it gives before a relearn procedure is started. It is this way on the 6spd too.
That's good to know. It always seemed weird that that if a transmission learns the shift points, it would unlearn whenever the battery was disconnected. Perhaps it's just the weather or I'm learning to drive it so that I mostly avoid the clunks. It does seem better lately though and it did seem to coincide with when I did the wheel. Also could be placebo effect. :unsure:
 

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HPtuners' VCM Scanner software can force a transmission re-learn, too. It'll do a quick re-learn, or a full.

And, from my experience, disconnecting the battery for a while does reset something because the transmission shifts better (in terms of speed/acceleration performance), and seems less mushy.
 

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HPtuners' VCM Scanner software can force a transmission re-learn, too. It'll do a quick re-learn, or a full.

And, from my experience, disconnecting the battery for a while does reset something because the transmission shifts better (in terms of speed/acceleration performance), and seems less mushy.
On the old trucks, a battery disconnect would reset shift compensations... ie line pressure, but not the adapted shifts themselves. With more line pressure or less depending, it should feel better.
 
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