Need some advice....8 speed GMC Transmission Problem (1 Viewer)

Logan T

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I purchased my 2018 GMC Sierra exactly a year ago and have 15,000 miles on it. It has been getting worse and worse lately on the stupid 8 speed transmission that GMC is under investigation about(Google Search: GMC 8 Speed Transmission Problems and you'll understand). From 1st to 2nd gear it will shift so hard and it feels like I'm getting rear ended on how hard it hits. It also feels like on cold start driving for a bit that the transmission is almost slipping. It's hard to describe but everywhere you look this up at we all have the same exact problems. People have said that GMC has listed a couple of things to do that fixes it for a short time but nothing truly works. They just keep trying these so called "fixes" so they can stall for the warranty to fall off for people that have the normal 36,000 mile warranty which I have cause I didn't buy extended warranty. I don't mind the 1st to 2nd gear hit but it's like I'm going to be having trouble with this transmission the entire time I have this truck and after warranty that's coming out of my pocket cause GMC doesn't care. There is a class action lawsuit against this. Some people file lemon law and are successful. I just don't know what to do as I wanted this to be a long term truck but it's getting really bad. I've already put so much money into this truck that trading it in would be a huge loss but at the same time I really don't want to have to deal with this and the GMC here that I have to deal with are a bunch of dumba****. This is like the 3rd car that I have been screwed over and I'm really getting sick of it.
If it was you what would you do?
 

Logan T

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Just do lemon law... the key is don’t accept the truck back if it’s still doing it.
It's going to be hard as this is the first time I've actually taken it in for service on this issue. At first it wasn't that bad but it's getting worse and worse
I'll also have to take the loss on all of the stuff I put into it.
 

GotWake

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I would take it back to the service department and keep track of the service history (business days in the shop and number of visits for the same problem). Then, once you meet the threshold for the lemon law, I would initiate the buyback. You can do it for yourself through the BBB. But, the rate they use isn’t the same as the lemon law.

My 2015 trans was doing the same thing literally right at the end of the warranty. They fixed it and and it started doing the crap again a few months later. I traded it immediately.
 

rider9195

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Is the 1-2 shift the only one that is harsh? Does the shift seem delayed? Does this only happen during the first shift of the day after the vehicle has sat and cold soaked? I work on them daily and it keeps me busy..this is one of the many issues the 8 speed has.

Sad to say but GM considers this condition normal due to the C4 clutch fill time and says it will not change durability of transmission. Which if you bring it into a dealer they may say this.

With that said, this is generally a simple fix and I have successfully made the 1-2 shift smooth on many with just a few requiring valve body replacement. BUT there is always a short delay no matter what you do, even after a new transmission. Having the short delay on the first 1-2 shift of the day to me is acceptable, but slamming into 2nd is most certainly not.

If the TCM has the latest update all it should need is a drive learn. This basically will single out a certain clutch pack to learn pressure and volume. In the 1-2 case, the C4 clutch would need to be learned and is actually very simple and you could do it yourself with no tools required. Message me if you want some more information on this.
 

CobawLT2010

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Is the 1-2 shift the only one that is harsh? Does the shift seem delayed? Does this only happen during the first shift of the day after the vehicle has sat and cold soaked? I work on them daily and it keeps me busy..this is one of the many issues the 8 speed has.

Sad to say but GM considers this condition normal due to the C4 clutch fill time and says it will not change durability of transmission. Which if you bring it into a dealer they may say this.

With that said, this is generally a simple fix and I have successfully made the 1-2 shift smooth on many with just a few requiring valve body replacement. BUT there is always a short delay no matter what you do, even after a new transmission. Having the short delay on the first 1-2 shift of the day to me is acceptable, but slamming into 2nd is most certainly not.

If the TCM has the latest update all it should need is a drive learn. This basically will single out a certain clutch pack to learn pressure and volume. In the 1-2 case, the C4 clutch would need to be learned and is actually very simple and you could do it yourself with no tools required. Message me if you want some more information on this.
You will be initiating the re learn procedure literally every oil change if you want to keep it smooth.

This is literally the same issue I had with the ZF 9 speed. It’s a hardware issue no matter which way you look at it. Trade it or lemon law it.

I was super happy when my Chrysler was totaled so I didn’t have to deal with a ****ty trans anymore. More gears are not the solution... I’m not sure when car brands will acknowledge that.
 

rider9195

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You will be initiating the re learn procedure literally every oil change if you want to keep it smooth.

This is literally the same issue I had with the ZF 9 speed. It’s a hardware issue no matter which way you look at it. Trade it or lemon law it.

I was super happy when my Chrysler was totaled so I didn’t have to deal with a ****ty trans anymore. More gears are not the solution... I’m not sure when car brands will acknowledge that.
There are two types of learns on them, service fast learns will erase all the shift adapts and start from fresh. The drive learn just fine tunes each one individually but you have to drive it in a certain gear, RPM range, over a certain distance.

I personally have only had once come back 10k later with similar shift issue and valve body was replaced. They really aren't a terrible transmission unless you do city driving.

The 10 speed is a huge improvement overall compared the 8 speed. Don't even get me started with the 9 speed in the cars and crossovers what a nightmare...
 

Logan T

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Yes it mostly happens from a cold start after it has been sitting for awhile. It's worse the longer it sits. Literally feels like when it shifts to 2nd gear that it stalls then I feel like I'm getting rear ended. It also stutters at times when driving around it almost feels like it doesn't know what gear to be in and it feels like it's almost slipping or something.

I just got the truck back and this is what it says on the service sheet: test drove when driving and the tcc is apply with gds 2 the is a shudder slip speed rpm jumping per pil8-na-335 20 qts of hp fluid was changed and trans cooler and line were flushed out and cleared with brake cleaner fluid level was set then test drove to shudder was not present completling repair
 
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rider9195

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Yes it mostly happens from a cold start after it has been sitting for awhile. It's worse the longer it sits. Literally feels like when it shifts to 2nd gear that it stalls then I feel like I'm getting rear ended. It also stutters at times when driving around it almost feels like it doesn't know what gear to be in and it feels like it's almost slipping or something
Sounds like they did the fluid exchange for a torque converter shudder issue. Mobil 1 came out with a new fluid being the old HP fluid was hydroscopic (absorbs moisture). They require 200 miles and two cold to hot soaks before re evaluating that condition. At this point it is documented with GM and that truly does help if something does decide to let go out of warranty. I assume that the powertrain warranty is covered for 5 years 60K.
 

Logan T

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Sounds like they did the fluid exchange for a torque converter shudder issue. Mobil 1 came out with a new fluid being the old HP fluid was hydroscopic (absorbs moisture). They require 200 miles and two cold to hot soaks before re evaluating that condition. At this point it is documented with GM and that truly does help if something does decide to let go out of warranty. I assume that the powertrain warranty is covered for 5 years 60K.
Everywhere online that I've seen about this issue people state that GMC does a bunch of different "fixes" but nothing really helps. It helps for about 2-3 months then the problem comes back and sometimes it comes back with more problems and even worse.
 

Buz

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Is the 1-2 shift the only one that is harsh? Does the shift seem delayed? Does this only happen during the first shift of the day after the vehicle has sat and cold soaked? I work on them daily and it keeps me busy..this is one of the many issues the 8 speed has.

Sad to say but GM considers this condition normal due to the C4 clutch fill time and says it will not change durability of transmission. Which if you bring it into a dealer they may say this.

With that said, this is generally a simple fix and I have successfully made the 1-2 shift smooth on many with just a few requiring valve body replacement. BUT there is always a short delay no matter what you do, even after a new transmission. Having the short delay on the first 1-2 shift of the day to me is acceptable, but slamming into 2nd is most certainly not.

If the TCM has the latest update all it should need is a drive learn. This basically will single out a certain clutch pack to learn pressure and volume. In the 1-2 case, the C4 clutch would need to be learned and is actually very simple and you could do it yourself with no tools required. Message me if you want some more information on this.
With all due respect, and not directed at you, what a bunch of workaround malarkey! I’ve had cars back in the 80’s and 90’s with beautifully smooth transmissions.
The problem is with the ever tightening CAFE standards we are cramming way too many gears into transmissions and over complicating them.
I have a 10 speed in my f150. It’s the jerkiest vehicle I’ve ever had. It may have something to do with being turbocharged but even coming to a stop involves way too much transmission jitter.
 

Mad Hatter

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I had this issue on my 2014 Hyundai Genesis sedan a couple years ago, which also has an 8 speed adaptive transmission. Took it in twice to have in re-learned; both times that worked for about a week, then it was back to jerky upshifts, some to the point where you're glad you have a seat belt on. Sadly the only solution was a new transmission.
 

rider9195

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Everywhere online that I've seen about this issue people state that GMC does a bunch of different "fixes" but nothing really helps. It helps for about 2-3 months then the problem comes back and sometimes it comes back with more problems and even worse.
The 15-17 variants are highly problematic, 18 and 19 so far have been ok. If the guy doing the learn isn't experienced with the procedures it won't feel quite right. I have spent 4 hours before driving a truck to get it to shift perfect in my opinion. GM labor times do not pay great for technicians and most flat rate guys will not spend more than they need to. It is overall silly and agree it is jumping through hoops at times.

With all due respect, and not directed at you, what a bunch of workaround malarkey! I’ve had cars back in the 80’s and 90’s with beautifully smooth transmissions.
The problem is with the ever tightening CAFE standards we are cramming way too many gears into transmissions and over complicating them.
I have a 10 speed in my f150. It’s the jerkiest vehicle I’ve ever had. It may have something to do with being turbocharged but even coming to a stop involves way too much transmission jitter.
Totally agree. Each year there is something new and I just think to myself all the issues it will be. It is amazing how much they stuff in them and to go drive an old 4L80 4 speed and the thing shifts flawlessly for such a basic transmission.
 

doubledge

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LEMON LAW!

I would continue to bring it in and when you reach the criteria use the lemon law. There are plenty of people having this issue if there is an investigation and class action law suit. Just get rid of it. You will never be completely happy with it.
-- Double Post Merged: --
Transmission issues are one of those few items that are hard to just fix. I would also never trust the dealer when they say it won't affect longevity.
 
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Logan T

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I think I'm past the point of Lemon Law. I've had it for a year and I haven't taken into service until today. It wasn't that bad starting out but again it keeps getting worse and worse so it was time to take it in.
I wish I would of researched this way before when it first started happening. I just learned about the class action law suit and the investigation two nights ago.
 
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SWB

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I can tell here in Arkansas car lots are full of used new model Chevrolet and GMC pickups. I have heard from several people about tranny issues. I wish you luck. I would try to get out of that seat as soon as you can.
 

Buz

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I think I'm past the point of Lemon Law. I've had it for a year and I haven't taken into service until today. It wasn't that bad starting out but again it keeps getting worse and worse so it was time to take it in.
I wish I would of researched this way before when it first started happening. I just learned about the class action law suit and the investigation two nights ago.
You can definitely lemon law that truck. Especially in Florida. The law is on your side here. As long as you can show after three attempts that the issue still exists they have to buy it back. It’s a lot of work and you have to provide evidence that it is an issue. GM will try to scare you into thinking you have to keep the truck. They will not give you full new value for your truck however. It will be an adjusted amount based on mileage. But you can force them to buy it back if you’re willing to put in the time.
 

knight_man

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I tried to consider trading off one of my scoobies for a truck but it seems like no matter what make or model I pick, my 2 choices are 1:a slipping transmission or 2:a rusted frame... cheaper to tear up a rental when I need a truck.

You guys think we are we getting harder on transmissions (new vehicles have a lot of power in comparison to older ones) or are they just being over engineered and poorly designed?

OP, Good luck man. That truck is way too new for that crap. Start complaining and get that lemon moving!
 

Th3 Factory Freak

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This is like the 3rd car that I have been screwed over and I'm really getting sick of it.
If it was you what would you do?
So all 3 cars you purchased were a GM vehicle?
 

Buz

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I came to the conclusion years ago that all new cars are junk. All of them.
Really they’re just a compilation of metal, plastic, rubber and glass that never harmonize as well as you’d like them to.
They’re all disappointments.
 
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