2015 GMC Denali 6.2/8-speed shifting noise when cold

[jgedde]

I think you missed my sarcasm...my buddy is now on his THIRD truck, he now has an 8 speed 6.2 denali fully fully loaded, had a '14 5.3 6 speed denali, and before that a 5.3 6 speed SLT. Now he is complaining about this one too - tranny, throttle tip in, power isn't as advertised (maybe he should try breaking it in though thing has all of 500 miles lol)

 

Bottom line is, I have never, EVER been to a forum w/ so many constant complaints. Is my truck perfect? NO, but I'm going to live with it because nothing in life is perfect and the grass is always greener etc. That, and the fact that GM royally F****D every single loyal owner in the rear that bought a 2014 early on w/ this absolutely RIDICULOUS rebates and incentives has completely turned my off from the badge, I don't even want to look at the dealers let alone step foot on the lot, so I'm all set with trading up or sideways for another (been there).

My real advice is, just like the 6 speeds, wait until some reputable tuner has tunes available and/or head to the dyno. I don't know what it is exactly about GM and their transmission programming, but it is essentially the worst in the industry IMO - and a big detractor for me. The clunking, delayed shifts, rpm surges in seemingly neutral, confusion of when to up or down shift, refusal to shift, and bad behavior in the cold? Yeah, that is pretty much par for the course from GM.

 

I should know - 3 trucks, a G8 GT, and a caddy CTS should be enough of a test sample..

Amen brother! I'm with you 100% about the GM tranny programming as of late. I'm really dissapointed to hear the 8-speeds have issues too. I posted not too long ago how much I hated my Sierra because of tranny programming issues and throttle response. The good news is Justin at Black Bear made my truck IMMENSELY better. He did what GM should have

 

John

[Gunner99]

Almost 3300 miles on it now. The transmissions has been replaced and the clunking I had when I accelerated from a stop appears to be gone.

I'll put a few hundred miles on it to make sure its fixed because it took about that long for the initial clunking to appear in the first place.

This isn't even my truck anymore. I feel like everyone has driven it almost like a chicks whose been gang-banged by the football team then turned back over to me.

 

Its in the body shop now being addressed for the scratches going down the sides of the truck and the third brake light was replaced from them running it through their automated car wash. When I get it back probably Tuesday I'll put the miles on it and let you guys know how she drives. hopefully your 8 speed trannys are either not defective clutchpacks like mine or they replace them altogether fast.

When I test drove it with the service manager today it seemed to be gone and shifted a lot better because they updated the tranny with #PI1388 update.

 

http://www.silveradosierra.com/ecotec3-6-2l-v8/my-awesome-review-50-000-denali-6-2-8speed-t333770-80.html#p3673258

 

Here is a detailed thread I made about my experiences with this ordeal.

[Ashtonman]

It's been about 45 days or so since I posted last about my clunk noise. I have over 5k miles on my truck and have used it in both 4x2 and 4x4 this winter. I have had it in the shop three times for the transmission and I love the truck except for the transmission clunk. What drives me crazy is it will not clunk for a few miles, and then clunk for the next few miles at each stop. It does not make any mechanical sense to me. I don't understand how it can work just fine for several miles and then cluck away for the next few. Is anyone else seeing it come and go.

[BuyAmericanIron]

Mine is doing exactly the same thing listed above. Sometimes it clunks, other times it is silent. Seems to be worse when cold. Maybe warm weather will make it go away..... Cannot duplicate it consistently making it hard to diagnose. Will take it to the dealer soon for the update. Hope that cures the problem. Yes, I love the truck but don't like the transmission. Too bad the flagship truck has this problem. Then there are the headlamps....... Will probably install HID soon to resolve that problem. Shouldn't have to do that when you pay $50K for a top of the line vehicle.

[Grand_Cherokee]

cant believe you GM owners of the 8-speed are having very similar cold shifting issues as us Jeep owners. Our trannies are ZF based (the one is my Jeep and all V6 Chryslers that have the 8 speed) are ZF based with some chrysler tinkering with it (the 845RE). The V8 HEMI's and Diesels have the pure German ZF trannies. Can you guess which one has the most problems? I think your GM 8 speeds are not ZF based but bet you the core insides are all the same. For us mopar owners, its the same thing, in the cold the 1-2 shift is bad, like it delays going into second gear and the engine does a bit of reving. Sure we you can re-flash and re-learn, if that doesnt work, its a new valve body, if that doesnt work, its a new transmission and then that doesnt quarantee the problem wont come back.

 

My take is the software is not ready yet. When the tranny is cold the fliud (which is not ATF, but rather hydrallic fuild like in your elevator) doesnt flow fast enough. Now, the question remains, is that the vavle isnt opening enough or the fluid can flow fast enough? If its the vavle, sure software can correct for this but if its the latter, than there is a hardware design flaw somewhere and this will take longer to fix (if any).

 

Read a comment on this thread about your Ford/Dodge friends commenting on the issues on your 8 speed issues. Well I can quarantee you the Dodge friend doesnt have the 8 speed.

[jonboy77]

I will be taking my 2015 in for service tomorrow. Man, what a pain in the butt. I have a SLT with the 5.3 and notices problems at around a 1000 miles. When ever inlet off the gas between 30-45 mph while the truck is still gaining speed for the gear it is in I noticed a delay them a LOUD clunking notice. Only happens when downshifting but it's terrible.

[GMCustomerService]

I will be taking my 2015 in for service tomorrow. Man, what a pain in the butt. I have a SLT with the 5.3 and notices problems at around a 1000 miles. When ever inlet off the gas between 30-45 mph while the truck is still gaining speed for the gear it is in I noticed a delay them a LOUD clunking notice. Only happens when downshifting but it's terrible.

 

Hey John,

 

Sorry to hear you're experiencing this clunking noise in your Sierra. Is it still at the dealer? Please feel free to send us a PM if you'd like for us to follow up and discuss further. We're happy to provide an extra layer of assistance if needed.

 

Sincerely,

 

Eddie A.

GM Customer Care

[CP1]

Mine does the same thing. 2015 GMC Sierra denali. 6.2, 8 spd. 10,500 mi. Under 40 mph, clunk and clang. Over 50 not too bad. Pull out of a stop light and people look at you like "What did he just lose?". A $60k piece of junk. I'm thinking of trading for 6 spd while they are still out there. I hear they converting ALL of them over to the 8 spd. BAD idea!! My 2 cents.

[GMCustomerService]

Mine does the same thing. 2015 GMC Sierra denali. 6.2, 8 spd. 10,500 mi. Under 40 mph, clunk and clang. Over 50 not too bad. Pull out of a stop light and people look at you like "What did he just lose?". A $60k piece of junk. I'm thinking of trading for 6 spd while they are still out there. I hear they converting ALL of them over to the 8 spd. BAD idea!! My 2 cents.

Hey CP1,

 

I am sorry that you are having a shifting noise concern with your Sierra. Have you had it diagnosed by a dealership? If not, I would be happy to contact a dealer on your behalf so they can look into this for you. Please send me a PM if you are interested in this.

 

Best,

 

Anthony Z.

Gm Customer Care

[CP1]

I am going to contact the dealer next week. I pulled a trailer, all the way north, from Florida, over the last couple of days. It seems decent on the highway. It shifts smooth as silk. But its a piece of crap at low speeds. It doesn't seem to know whether to upshift or downshift. Sometimes it doesn't know when to go in gear at all. If this thing makes 30,000 miles it will be a miracle. Its a good thing it has a 100,000 mi warranty. I will post the outcome at the dealership.

[Stitches040]

I am going to contact the dealer next week. I pulled a trailer, all the way north, from Florida, over the last couple of days. It seems decent on the highway. It shifts smooth as silk. But its a piece of crap at low speeds. It doesn't seem to know whether to upshift or downshift. Sometimes it doesn't know when to go in gear at all. If this thing makes 30,000 miles it will be a miracle. Its a good thing it has a 100,000 mi warranty. I will post the outcome at the dealership.

 

I'm with you.

 

I have a 2015 GMC Sierra All-Terrain with the 6.2L / 8-Speed in it. It clunks so hard, I swear the rear diff is going to fall out sometimes. I too have found that the transmission does not know what gear choose. At lower speeds, it gets confused and some of the downshifts cause the harsh clunk/bang. I do notice it more, when the truck is cold and I'm going short distances.

 

I have 8700 miles on it, and it seems to be getting worse.

 

My truck goes in for it's second service in Mid August. I'll ask them to check to see if the service bulletin has been done.

[Badass69]

Take it in. They have enough TSB's for various problems on the 8 speed now that you will get some form of resolution to it.