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

Ashtonman

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lba0213 Enthusiast

lba0213

Posted
Posted

Thanks, being that my truck was built mid to late december and delivered to the dealer first week of january, would it be safe to assume this update was done to my truck before I picked it up? Bc it sure doesnt feel like it.

 

BTW putting it in M7 really seems to smooth things out.

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BluByU14 Enthusiast

BluByU14

Posted
Posted

Thanks, being that my truck was built mid to late december and delivered to the dealer first week of january, would it be safe to assume this update was done to my truck before I picked it up? Bc it sure doesnt feel like it.

 

BTW putting it in M7 really seems to smooth things out.

 

Mine was built and delivered in the same time frame, so I would say that your trans has not been updated if you are experiencing problems (clunky/awkward shifting). I simply forward my service adviser the service bulletin number...brought it in and they did the update on the spot.

lba0213 Enthusiast

lba0213

Posted
Posted

 

Mine was built and delivered in the same time frame, so I would say that your trans has not been updated if you are experiencing problems (clunky/awkward shifting). I simply forward my service adviser the service bulletin number...brought it in and they did the update on the spot.

 

I sent the service bulletin to my dealer but they said it didnt pertain to my VIN, but they would be happy to do it anyways. Did your VIN match those listed in the service update by chance?

Ashtonman Enthusiast

Ashtonman

Posted
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Posted

My vin matched, built 10/14. My understanding is that this was for all 8-speed equipped vehicles. Yours might have been flashed before you received it. According to the tech that has been working on my truck, there was another update released in mid-January.

CounterMeasure Enthusiast

CounterMeasure

Posted
Posted

Mine has the slight clunk when taking off from a stop, and its been there since day one. Nothing excessive, just normal light pedal. It only does it when cold too. The TSB 14876 didn't help it. It goes into the dealer tomorrow to see what it is, along with some rough shifting.

 

The clunk is *very* similar to the "hill start" releasing when you accelerate. Maybe related? I guess I will find out more tomorrow. :)

TX14Z71 Enthusiast

TX14Z71

Posted
Posted

The other day I started my truck and felt what I describe as a bump from the back end. I turned off the truck and turned it back on and felt the same thing. I dogs it a few times before finally taking off. My truck had the service bulletin performed and still issues. I'm curious about this most recent update.

CounterMeasure Enthusiast

CounterMeasure

Posted
Posted

Got mine truck back from the dealership today. The initial clunk is still unknown. They said they made sure everything is tight in the driveline. The tranny isn't showing any diagnostic problems, such as TC slipping and what not. So no luck there. I have been able to reproduce it better by coming to a stop (even very gently to prevent dive), sit 20 or so seconds like waiting on a stop light, then gently apply the accelerator. If I am very gentle, its more a click than a clunk, but it still happens. Still, doesn't help when the dealership can't reliably produce it themselves to figure it out. I will get under it when the weather is nicer to see things for myself.

 

As for the harsher shifting at times, especially when going into 5th or 6th, I was given a better answer than the standard "that's normal". I was told "it's normal, as its a very busy transmission".

 

At least I didn't get my truck back with scratches, dings, or weak brake pedal like others have had happen. I am going to try a different dealership though.

Gunner99 Enthusiast

Gunner99

Posted
Posted

They just replaced my tranny because of that clunk noise. They said it was a defective clutch pack. I test drive it Tomorow to see how it is.

I believe I may have been the first to go through three dealers until they finally gave in with some real answers.3000 miles built 10/14 gm tach told dealer the update would fix it but then they said it wouldn't and parts were on back order then just replaced entire unit.

TX14Z71 Enthusiast

TX14Z71

Posted
Posted

They just replaced my tranny because of that clunk noise. They said it was a defective clutch pack. I test drive it Tomorow to see how it is.

I believe I may have been the first to go through three dealers until they finally gave in with some real answers.3000 miles built 10/14 gm tach told dealer the update would fix it but then they said it wouldn't and parts were on back order then just replaced entire unit.

I'm really excited to hear about that test drive.
Gunner99 Enthusiast

Gunner99

Posted
Posted

I'm really excited to hear about that test drive.

Well tranny is installed. They wanted to keep the truck and put 80-100 miles on it so tranny can learn shift points. He didn't want me to pick it up until its completely ready.

TX14Z71 Enthusiast

TX14Z71

Posted
Posted

Well tranny is installed. They wanted to keep the truck and put 80-100 miles on it so tranny can learn shift points. He didn't want me to pick it up until its completely ready.

Ok, just let us know as soon as you can. Appreciate it.
thetruck454 Enthusiast

thetruck454

Posted
Posted

Well tranny is installed. They wanted to keep the truck and put 80-100 miles on it so tranny can learn shift points. He didn't want me to pick it up until its completely ready.

While I completely believe that is their intent, my mind couldn't help but think it meant "The tech is going to beat the ever living snot out of it for 80-100 miles without warming it up to make sure works". I have trust issues....

BluByU14 Enthusiast

BluByU14

Posted
Posted

 

I sent the service bulletin to my dealer but they said it didnt pertain to my VIN, but they would be happy to do it anyways. Did your VIN match those listed in the service update by chance?

 

No it did not, but they still did the update and it significantly helped my trans. Once I got it back it was like I had a new transmission.

CounterMeasure Enthusiast

CounterMeasure

Posted
Posted

 

No it did not, but they still did the update and it significantly helped my trans. Once I got it back it was like I had a new transmission.

If you are referring to TSB 14876, it isn't an "update" per se. If you read the TSB, all they are doing is using a Tech2 to go back into re-learn mode, which makes the transmission forget all its saved shift values to make new ones. This first puts it in uber-conservative shifting, where you can really tell the throttle comes off, the shift happens, and it tips back in. They can do that to any truck all day long.

 

The issue for specific VINs was that certain "bad" values were introduced by flashing software in the factory that cause it to use those by default. Mine was one of them, and it went from banging around in the shifting right off the carrier, smooth after re-learn, to slowly harder shifting as the miles added up.

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