Infamous 8 Speed Transmission Clunk - Dealer/GM Current Position on the Issue?

flyingfool · February 2, 2021

1 hour ago, LunkerHunter said:

Can disabling the TCC system for the first 4-5 gears be accomplished with the Diablo i3?

Sent from my iPhone using Tapatalk

call them and ask... i believe diablo can modify remotly and send you a file to install in the truck with thier tuner., i suggest buying hptuners, you will have to pay for unlock and the truck credits

Edited February 2, 2021 by flyingfool

sgiangregorio · February 3, 2021

My Sierra is at the dealer today for the clunk and shutter. Of course they said they can't reproduce, so they asked to keep it overnight so they could drive it when cold in the morning. That's fine, but since it doesn't do it every time, they may not feel it. I asked if they could just apply the TSB and do the fluid change, but they said they have to be able to reproduce it. The bumper to bumper warranty is up in 1000 miles, would the powertrain warranty still cover me till the 60K if they don't do the fluid before the bumper to bumper is over?

reardiff · February 4, 2021

9 hours ago, sgiangregorio said:

I asked if they could just apply the TSB and do the fluid change, but they said they have to be able to reproduce it.

Not true... Below is the TSB and clearly says diagnosis beyond the customer compliant is not required. I would print the TSB and bring it with you and show them this then see if they will do it with out being able to reproduce it. For what it's worth, I had the same clunks, harsh down shifts and then the TCC shudder. Once they did the fluid exchange all of that was gone. So far it's been about six months and no issues, drives like it should finally. This was done under power train warranty after bumper to bumper had run out.

Edited February 4, 2021 by reardiff

sgiangregorio · February 4, 2021

36 minutes ago, reardiff said:

Not true... Below is the TSB and clearly says diagnosis beyond the customer compliant is not required. I would print the TSB and bring it with you and show them this then see if they will do it with out being able to reproduce it. For what it's worth, I had the same clunks, harsh down shifts and then the TCC shudder. Once they did the fluid exchange all of that was gone. So far it's been about six months and no issues, drives like it should finally. This was done under power train warranty after bumper to bumper had run out.

Thanks. I didn’t catch that in the TSB. I would have pushed back today when they said “we don’t just fix things we can’t reproduce.” If he tells me tomorrow the same thing I’ll point him to this. I brought the TSB this morning and he said he didn’t need it, that they would look up TSBs themselves and apply them as required.

reardiff · February 4, 2021

This is also covered under the 5 year / 60k power train warranty so even once your 3/36 is up you still have coverage should the shutter come back or need a new TC. Although I will say it was night and day difference on mine, immediate improvement on the clunks and harsh down shifts. Some say the shutter comes back after a few thousand miles so we'll see, but for now the new fluid certainly was noticeable a improvement. And you get new fresh fluid exchange at 35k miles for free ; )

Edited February 4, 2021 by reardiff

sgiangregorio · February 4, 2021

13 minutes ago, reardiff said:

This is also covered under the 5 year / 60k power train warranty so even once your 3/36 is up you still have coverage should the shutter come back or need a new TC. Although I will say it was night and day difference on mine, immediate improvement on the clunks and harsh down shifts. Some say the shutter comes back after a few thousand miles so we'll see, but for now the new fluid certainly was noticeable a improvement. And you get new fresh fluid exchange at 35k miles for free ; )

Thanks. Here’s to hoping I don’t have to get too firm with the service writer to make it happen.

mcbartell · February 4, 2021

I just purchased my 2017 Sierra Denali from a GM dealer with 61,9XX miles. On the test drive I did not notice the transmission stuttering nor for the first drive one hour home. Through out the next 2 weeks I progressively noticed it more and more. When I finally took a longer drive at highway speeds the stutter was undeniable. Called the dealership and they were very willing to do a transmission flush at no cost to me. 1 Hour later I was back on the road and the truck drives perfect.

flyingfool · February 4, 2021

7 hours ago, mcbartell said:

I just purchased my 2017 Sierra Denali from a GM dealer with 61,9XX miles. On the test drive I did not notice the transmission stuttering nor for the first drive one hour home. Through out the next 2 weeks I progressively noticed it more and more. When I finally took a longer drive at highway speeds the stutter was undeniable. Called the dealership and they were very willing to do a transmission flush at no cost to me. 1 Hour later I was back on the road and the truck drives perfect.

they probably installed a software flash to the truck, fluid change wont make a night or day difference in driveability

sgiangregorio · February 4, 2021

Just had a nice argument with the service advisor now on their second day with my truck. He said the tech reads all the same stuff I can. I said great, then he knows it doesn’t matter if he feels it or not he should do it. He said the tech is going to drive it for the first time today in a few minutes. I told him I really don’t care if he feels it or not because it’s there and per the TSB they can do it on my word. So he should talk to his service manager and/or call GM but I expect it to be done. Frustrating.

sgiangregorio · February 4, 2021

And just got the follow up call that the tech felt the hard clunk from 1-2 and then again from 2-1, so he's doing the trans fluid change now. Also had the rear window recall done, the wireless charger harness replaced, and the console lid replaced (elbow divet) under warranty.

sgiangregorio · February 4, 2021

And to round this out, what a huge difference in the transmission with the new fluid. Honestly, it's not even like the same truck. Very smooth. Very. If this lasts, I'm a happy camper.

rockusaf · February 6, 2021

I've only had my 2017 for a few months and it has just over 41K miles (it was a lease turn in) and it does clunk at times. Most of the time I notice it is downshifting from 2 to 1 and usually it's when I'm just getting off the gas but I have no idea if it has ever had the fluid changed, is there a way to check before I take it to the dealer?

Rock

JimCost2014 · February 6, 2021

1 hour ago, rockusaf said:

I've only had my 2017 for a few months and it has just over 41K miles (it was a lease turn in) and it does clunk at times. Most of the time I notice it is downshifting from 2 to 1 and usually it's when I'm just getting off the gas but I have no idea if it has ever had the fluid changed, is there a way to check before I take it to the dealer?

Rock

If were a lease, there should be pretty detailed service records from the person who had it before at the dealership it was leased from (hopefully).

If the fluid was changed under the TSB (warranty), your VIN should reflect that if checked.

dgstarr63 · February 7, 2021

My 2021 5.3 8 speed has started to clunk when slowing to a stop light. It was perfect until 1200 miles. My dealer told me that they had not seen any 8 speed issues since the 2019 models. I haven't taken it in yet. Has anyone else had problems with the newer truck 8 speeds?

flyingfool · February 8, 2021

17 hours ago, dgstarr63 said:

My 2021 5.3 8 speed has started to clunk when slowing to a stop light. It was perfect until 1200 miles. My dealer told me that they had not seen any 8 speed issues since the 2019 models. I haven't taken it in yet. Has anyone else had problems with the newer truck 8 speeds?

try using manual gear mode, select the best gear for the situation. dont use the last gear as this usually activates DoD and might contribute to hesitation, and clunks, so 8spd drive in 7th gear and feel it out