6L90E (gas truck) 2-1 downshift CLUNK

Epsilon Plus · September 3, 2022

I've seen a few threads here dating back to 2021 and there's plenty of people on FB with the issue but has anyone inquired with a dealer or higher up the 2-1 clunk with the 6L90E (6-speed) trucks?

It's intermittent. Doesn't do it all the time. First 5,000 or so miles, shifts like butter. Now almost (again, intermittent but more often than not) I slow to a stop the truck dumps into first gear and CLUNK. Sometimes it's rough enough to jolt the truck and jostle loose items around. Based on the intermittent nature and when it's doing it (usually coasting to a stop between 5-15MPH) I'd say its a tuning issue. Second gear is a 2.360:1 ratio and is more than capable of coasting to a stop, and even taking back off right away at part throttle. There is no need for the truck to DUMP into a 4.030:1 first gear without a load pushing on it as if it's trying to brake a 18,000lb trailer. That's what Tow/Haul is supposed to be for. I could expect the trans to command first slowing to a stop at 10mph if it was in tow/haul and the truck felt a push on the back sensors. There's no need to be dropping it into first gear at running speed hauling sail boat fuel. The tuning should coast second all the way until a stop, then select first at rest, or upon more than 40% throttle if transitioning from slowing back to take off.

Maybe if enough people voice their concern the new "GM Customer Service" rep on this board can inquire. Again, if you ask me it's a simple tuning flash TSB fix and not some complicated mechanical warranty nightmare for them.

Thoughts?

(My truck is a 2022 BTW, November 2021 build)

Blatant · September 3, 2022

Mine does it, just like you describe. Feels almost like it could stall.

Also, when turning right. Blinker, slow down, coast, truck "super slows" rather than coast [ which is weird ], make turn coasting, truck gets confused and bump, clunk, choke and then lunge out, when gas applied. Hopefully explained that understandably / makes sense.

Googling yields this have been a problem for years before ours and folks are told " normal " gm tranny programming etc. Crying ass shame really on a 70k new truck. My 20 yr old toyota 4sp auto shifts and behaves better and more predictably. I really don't think gm gives AF.

Epilsonplus, where you located in southwest?

Edited September 3, 2022 by Blatant

newdude · September 3, 2022

The 6Ls have have had the same clunks and bumps since 2007. I had a 2012 (6L80), a 2015 (6L90), 2016 (6L50) and a 2019 (6L80), they all exhibited the same exact 2-3 flares, 2-1 downshift bumps and coasting clunks.

They are normal.

Edited September 3, 2022 by newdude

Epsilon Plus · September 8, 2022

Blatant: I'm in the Phoenix area.

If it's "normal" I can deal. My only real concern with the issue is longevity and damage to the drivetrain. If it's just a drivability inconvenience, it is what it is. I don't mind the heavy duty nature of the way the truck is (squealy brakes, stiff ride), its all par for the course with an HD. I just don't want my front U-Joint giving out early, planets going out...etc because of it.

If it can take it, than so be it.

Jayroc7113 · September 8, 2022

I am currently at the dealer with this exact problem with my 2022 2500 LT gasser. Clunk is so loud you can hear the u joints bang and the truck tugs like it binds up for 2 seconds. The stall when turning at 15 mph is ridiculous. Never had this issue until 19k miles. Waiting to see what they say. After the test drive the tech said it's horrible......

diyer2 · September 8, 2022

My 2012 doesn't do it.

customboss · September 8, 2022

None of that is normal for a transmission. Normal for GM sure............warranty be dammed.

diyer2 · September 8, 2022

What is the cause? Mechanical or electrical/computer? If mine did this I would change the trans fluid to a 100% quality synthetic fluid. Worth a try.

Jayroc7113 · September 8, 2022

I tow a 7500 lb trailer daily. I use tow/haul mode when driving above 50 mph. When I made the appt with the dealer they told me to drive 2 weeks without towing so the adaptive transmission technology system could relearn the shift points while not towing. Sounded like BS but I did that anyway. Now the tech is checking the fluid level and color to see if it needs a fluid change. They are also checking for flash updates for the control module. They said they can make a case file to see what chevrolet tells them to do next. We will se what BS they give me to claim its normal....

Jayroc7113 · September 8, 2022

Well they got it corrected... tech said all the shift point pressures were way out of spec for every shift point. They flashed the computer with a patch from Chevrolet case files. I drove the truck and it's better than it was when I bought it. No banging or binding. No lag in throttle when turning. Noticed rpms are down around 1800 at 70 mph. Before it ran near 2000 ram. Fluid looked good and didnt smell burnt. Let's see how long it last..... hope this helps you guys!

Epsilon Plus · September 8, 2022

I'll take mine in and inquire about Jayroc's success.

I am sure it's adaptive/tuning related. If I had access to the ECM like I used to with my LSx cars I'm sure it could be massaged out.

GMCustomerService · September 9, 2022

On 9/3/2022 at 9:30 AM, Epsilon Plus said:

I've seen a few threads here dating back to 2021 and there's plenty of people on FB with the issue but has anyone inquired with a dealer or higher up the 2-1 clunk with the 6L90E (6-speed) trucks?

It's intermittent. Doesn't do it all the time. First 5,000 or so miles, shifts like butter. Now almost (again, intermittent but more often than not) I slow to a stop the truck dumps into first gear and CLUNK. Sometimes it's rough enough to jolt the truck and jostle loose items around. Based on the intermittent nature and when it's doing it (usually coasting to a stop between 5-15MPH) I'd say its a tuning issue. Second gear is a 2.360:1 ratio and is more than capable of coasting to a stop, and even taking back off right away at part throttle. There is no need for the truck to DUMP into a 4.030:1 first gear without a load pushing on it as if it's trying to brake a 18,000lb trailer. That's what Tow/Haul is supposed to be for. I could expect the trans to command first slowing to a stop at 10mph if it was in tow/haul and the truck felt a push on the back sensors. There's no need to be dropping it into first gear at running speed hauling sail boat fuel. The tuning should coast second all the way until a stop, then select first at rest, or upon more than 40% throttle if transitioning from slowing back to take off.

Maybe if enough people voice their concern the new "GM Customer Service" rep on this board can inquire. Again, if you ask me it's a simple tuning flash TSB fix and not some complicated mechanical warranty nightmare for them.

Thoughts?

(My truck is a 2022 BTW, November 2021 build)

This is certainly not what we like to hear, Epsilon Plus. Please know, customer satisfaction is extremely important to us. Our team would be more than happy to take a closer look into the concerns with your 2022 truck. To do so, please send an email to [email protected] with ATTN: Epsilon Plus/GM Trucks in the subject line.

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Blatant · September 13, 2022

stupid gm can'ed response, if it's even GM. ^^^^^

@Epsilon Plus east valley here. Let me know how you make out and the dealer you take it to OR if you reached out to the GM genie listed above and your result. Mine isn't bad, it's just not right and certainly not normal, imo, despite what is said, tsb's say etc. The fact folks have been talking about this for years / decade, sorta make it normal...crying ass shame.

All that said for longevity, these trucks are not toyota land cruisers, they are not going to get 300k on oem. It would be nice but is wishful thinking imo.

Edited September 13, 2022 by Blatant

netw0rks · September 19, 2022

Have a 3500 on order....following this thread closely. Appreciate any future updates/

Epsilon Plus · September 29, 2022

Took it to Chevy and because of GMs lack of planning and terrible supply chain I suppose all the techs (the few they have because they are probably still paying garbage piece rate and can't find anyone.....shocker) are so tied up they wanted a next day appointment. I don't have time off to waste so frivolously so I went to GMC and got the same spiel. Both service advisors acted like the issue was new information to them so I knew what was coming. "Tech couldn't replicate issue....blah blah". Especially since all the way there it was acting like a prince. I decided against wasting a valuable day off in the service bay for them to chase a squirrel.

I'm at the point where it is what it is. Hopefully someone with more time to spare and a bone to pick figures it out and Chevy releases a TSB that I can specifically point to, or if it's going to fail, it does so before November 2027 when the warranty is up (won't hit 60k by then).

Good luck but again, I think the issue is in the programming. Not exactly something a dealer can fix without an authorized and released TCM flash from the brass hats at GM.

Edited September 29, 2022 by Epsilon Plus