8 speed downshift clunk to 1st gear

Chevrolet1 · June 2, 2021

Here are the two updates to my 2019 Silverado 5.3L with 8-speed with only 7k miles on it, transmission now shifts great and no issues

2810875 (campaign number?) = Transmission control module reprogram to prevent hard downshifts to first gear when decelerating (feels like you're being bumped by the car behind you)

TSB-19-NA-121 = Torque converter / transmission shudder, which is like erratic shifting or the transmission seems to "hunt" for the right gear at times

Edited June 2, 2021 by Chevrolet1

vancealot29 · June 2, 2021

14 hours ago, Chevrolet1 said:

2810875 (campaign number?) = Transmission control module reprogram to prevent hard downshifts to first gear when decelerating (feels like you're being bumped by the car behind you)

Do you have any other info pertaining to this update? My 2019 5.3 8spd LTZ needs this ASAP. I've had it in three different dealerships, bugged GM on Twitter and still have gotten nowhere.

I just want to make sure I am armed with as much data as possible before calling the dealership again. I'm sure they hear "I saw it online" all the time.

Thanks in advance!

Chevrolet1 · June 2, 2021

21 hours ago, vancealot29 said:

Do you have any other info pertaining to this update? My 2019 5.3 8spd LTZ needs this ASAP. I've had it in three different dealerships, bugged GM on Twitter and still have gotten nowhere.

I just want to make sure I am armed with as much data as possible before calling the dealership again. I'm sure they hear "I saw it online" all the time.

Thanks in advance!

In addition to the TSB and campaign numbers in my original post, here are screenshots from the actual dealer services that were performed in March 2021. Hope this helps.

Edited June 3, 2021 by Chevrolet1

Adamace1 · June 3, 2021

Hummm... maybe I should take mine in and see if it can be reprogramed.. if any others find a fix please post here. Thank you

vancealot29 · June 3, 2021

20 hours ago, Chevrolet1 said:

In addition to the TSB and campaign numbers in my original post, here are screenshots from the actual dealer services that were performed in March 2021. Hope this helps.

Thanks for the info. I will give this a shot. All of my attempts were in 2020, so its possible something changed.

Chevrolet1 · June 3, 2021

1 minute ago, vancealot29 said:

Thanks for the info. I will give this a shot. All of my attempts were in 2020, so its possible something changed.

Welcome, and for my truck, these two updates fixed both issues. Truck shifts and drives great now, night and day difference. When I first spoke with the dealership in early March 2021 to schedule the appointment, they were aware and told me the fix would likely be a fluid flush, TCM reprogram, or both. This is one of the largest Chevy dealers in Houston and they sell a lot of trucks, so it seems their service department has dealt with it before.

GullLakeMi · June 3, 2021

Problems with 2016 8 speed are well known, not sure if same hardware. My 2016 did the stop light clunk and surge. Dealer said it was normal. I found it helped to tow around a 5k lb trailer, although not very practical. Then either things smoothed out or I couldn't feel it!

Recently swapped up to a 2021 w/10 speed. So far, night and day better. Knock wood.

Agriont · June 4, 2021

I have had several resets on the computer relearn. Flush and valve replacement as well as the TC. Problem remains. I've also experienced a surge, as if the truck wants to ignore the brake and push me through a stop while downshifting and coming to a stop or when stopped. Now getting a new transmission but still concerned. Note that GM extended the warranty for this problem. The issue is that warranty exists in case of a problem, not because of one. What does one do once the extended warranty is done? I'd jump to the ten speed but the loss on my truck would be significant and I believe GM should belly up with some incentive to owners who want to buy a replacement.

SummitWhiteT1 · June 4, 2021

does the 10 speed shift quicker than the 8 speed? Or is the night and day difference people talk about just the fact that it doesn't have the rough shifting?

Agriont · June 7, 2021

On 6/4/2021 at 12:54 PM, SummitWhiteT1 said:

does the 10 speed shift quicker than the 8 speed? Or is the night and day difference people talk about just the fact that it doesn't have the rough shifting?

From what I've heard from those who've purchased the ten speed, it is smooth. GM should be replacing problematic 8 speeds with the ten speed if it would fit.

VicFirth · June 20, 2021

I was getting a slight clunk during the same 3 to 1 as well. 2021 ZR2. I started to put it in Tow/Haul mode during stop and go/traffic type situations and I never get the rough downshift. Just tested it the last two days.

Edited June 20, 2021 by TunaFresh

dgstarr63 · June 20, 2021

I tried tow haul on mine and it did not work.

Adamace1 · June 20, 2021

I'm taking mine in Thursday. I will see if I get an update. I tried sport mode, tow haul mode, even tried shifting it myself but still does that hard downshift.

Agriont · June 21, 2021

14 hours ago, Adamace1 said:

I'm taking mine in Thursday. I will see if I get an update. I tried sport mode, tow haul mode, even tried shifting it myself but still does that hard downshift.

GM is replacing some transmissions but even this doesn't resolve the fact that these transmissions are faulty from factory. From 1st to 2nd to 3rd and back.. roughest transmission I ever had in a truck.

Adamace1 · June 24, 2021

On 6/21/2021 at 10:15 AM, Agriont said:

At dealership now hoping they will help with my transmission.

They didn't do anything. TCM has most current update, checked a TSB looking for twisted transmission lines. It wasn't actually doing it today. So I'm just going to ignore it. Luckily it only happens for one day every week or so.

Edited June 24, 2021 by Adamace1