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

Bob2C · October 28, 2019

Has anyone tried Lubegard additive?

mnm99 · October 31, 2019

On 10/28/2019 at 6:59 PM, Bob2C said:

Has anyone tried Lubegard additive?

How, it's a sealed transmission.

Cjc · November 9, 2019

On 2/19/2019 at 4:44 PM, Neal90 said:

My dealership tried to tell me the same thing then I sent them this

https://techlink.mynetworkcontent.com/?p=11127

at the end of it it states this

”Mobil 1 Synthetic LV ATF HP transmission fluid is required for all 8-speed transmission repairs regardless of the repair being completed.”

The new fluid is a requirement not an option for ALL 8 speeds.

I told it to the service writer just like that ( and I was polite) . Bringing g it sat to get the new fluid.

All I can say is wow.I had the fluid changed and the truck runs totally different,the shift points are better and no more clunking.Had to fight tooth and nail with my dealership to cover the cost,but they did.But don't get me wrong my truck didn't shutter at all,and would clunk once in a while.The service manager was useless,but the shop foreman was very helpful.Guss who came to my rescue to have it covered.A secretary from the back office,she says this is why I keep this work order in my desk,it states that changing the fluid is covered under the power train warranty.My service advisor didn't even know this.

elcamino · November 9, 2019

A service advisor is just a appointment taker and salesman. His job is to schedule work and sell the customer services.

Racso · November 16, 2019

W all I want to know is where do I join the class action law suit ? Got the transmission problems ? Where ? Phone number please

Bikemobile · November 19, 2019

New fluid made a huge difference on my 8 speed. Smoothed it out and cut the wierd clunks and bumps by 80-90%!

Nor Cal Z71 · December 6, 2019

I have had transmission issues with my 2018 Silverado LTZ CC 5.3 8-speed transmission since purchasing my truck new in December of 2017. The dealer reprogramed the trans computer shortly after purchase. This worked for a while, but at the next service, I had the 2-1 clunk and asked them to look at it. Service advisor said the trans was operating normally. I then looked up the problem on-line here and I found the same concerns I was having. I monitored the trans temps and found that the clunking was only occurring after the temps hit around 150-160 degrees (190-195 - typical fully warmed up temp). The trans would clunk into reverse sometimes at start-up, but the downshift clunk would only occur once the trans temp was 150+. I finally took the truck in when the clunking got really bad - park to reverse, 2-1, 3-2, etc. I had a service tech drive in the car and who felt the problems first hand with me and acknowledged. At this time Service advised me that a new valve body was needed and had to be ordered. It took a week to get this part to correct the issue. I've put 7,500 miles since repairs with no more clunking issues. I have noticed however, that my fuel economy has dropped 1-2 mpg and shifting points are a little different. I have noticed that the motor will rev a little higher and hold a little longer in between gears than before.

mnm99 · December 9, 2019

On 12/6/2019 at 5:45 PM, Nor Cal Z71 said:

I have had transmission issues with my 2018 Silverado LTZ CC 5.3 8-speed transmission since purchasing my truck new in December of 2017. The dealer reprogramed the trans computer shortly after purchase. This worked for a while, but at the next service, I had the 2-1 clunk and asked them to look at it. Service advisor said the trans was operating normally. I then looked up the problem on-line here and I found the same concerns I was having. I monitored the trans temps and found that the clunking was only occurring after the temps hit around 150-160 degrees (190-195 - typical fully warmed up temp). The trans would clunk into reverse sometimes at start-up, but the downshift clunk would only occur once the trans temp was 150+. I finally took the truck in when the clunking got really bad - park to reverse, 2-1, 3-2, etc. I had a service tech drive in the car and who felt the problems first hand with me and acknowledged. At this time Service advised me that a new valve body was needed and had to be ordered. It took a week to get this part to correct the issue. I've put 7,500 miles since repairs with no more clunking issues. I have noticed however, that my fuel economy has dropped 1-2 mpg and shifting points are a little different. I have noticed that the motor will rev a little higher and hold a little longer in between gears than before.

I went through the same thing as you. Took me 5 times and kept records showing it happened every time. every time they said it's normal. The last time I drove with them and he heard it. I guess they HAVE to do something now. Well they did the valve body and fluid change. The problem was gone until around 112 miles later. Heard my first 2-1 clunk. It doesn't happen as much, but now I have a random clunk when it hits 5th gear. When it's cold it happens all the time first starting out. When the tranny warms up it's random. It will lurch forward sometimes when coming to a stop then giving a little gas, Like it doesn't know what gear it's in.

As for the class action. I'll let you guys know how it goes, that's all I can say, sorry.

Nor Cal Z71 · December 10, 2019

On 12/9/2019 at 2:43 AM, mnm99 said:

It doesn't happen as much, but now I have a random clunk when it hits 5th gear.

Forgot to mention, my transmission will sometimes hold way long in 5th - like to 4000 RPM. Mostly while getting on the freeway with no demand on the engine for it to rev this high and no urgency. I was attributing this to holding longer as stated in my previous post, but sounds similar to your issue.

mnm99 · December 10, 2019

5 hours ago, Nor Cal Z71 said:

Forgot to mention, my transmission will sometimes hold way long in 5th - like to 4000 RPM. Mostly while getting on the freeway with no demand on the engine for it to rev this high and no urgency. I was attributing this to holding longer as stated in my previous post, but sounds similar to your issue.

When you get in the car when it's cold , start it up and just start driving , do you get a clunk noise when it hits 5th gear?

Nor Cal Z71 · December 13, 2019

Not that I have noticed.

Agriont · February 21, 2020

I have a 2017 Sierra Denali 6.2 4wd. I've only heard a clunk when coming to a stop at low speed just after a cold start. Doesn't happen every time, but very noticeable when it does. I've read some folks refer to something similar with their trucks. I've got about 20k miles on it.

Bikemobile · February 24, 2020

Tell the dealer the transmission clunks and feels like you are “driving on rumble strips.” Those words are searchable in their diagnosis network. They will change the fluid for free.

Tsb