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Chad2815

By Chad2815
in Engines & Drivetrain

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SeekAndDestroy Enthusiast

SeekAndDestroy

Posted
Posted
2 hours ago, Chad2815 said:

 

https://gm-techlink.com/?p=7962

 

I would try the easy stuff first. Change fluid, and flash the tranny. Could also be numerous other things like leaf springs, or rear end play. If you have to change the torque converter then your tranny will be out or pulled back from the engine. Then you might be able to check crankshaft play. The easiest way to check this is with the engine on a stand. I hope it’s not your crank. Good luck!

Chad2815 Enthusiast

Chad2815

Posted
  • Author
Posted

Crazy stuff....I have had the flush numerous times for the vibrations but the downshift from third to second is new. I just wanted to post so others knew, that was news to me. I am still under warranty but I am sorta exhausted with the process. Thanks for the input though.

roadkill5.3 Enthusiast

roadkill5.3

Posted
Posted (edited)

i just got tuned by black bear, and all down shift clunking is gone. what a difference on shifting, engine, etc. totally new truck. 

what my point is, tuning can fix the clunks. the way GM has programmed these trucks is asinine. too many up shifts to quick, constant lugging, wanting to increase fuel economy to gov regulations. i dont think its setup correctly/synchronized correctly with tranny and engine setpoints. 

but hey, im not an engineer. 

 

30k miles. my warranty is up in 2 months anyway. 

Edited by Jgreen2193
Chad2815 Enthusiast

Chad2815

Posted
  • Author
Posted
57 minutes ago, Jgreen2193 said:

i just got tuned by black bear, and all down shift clunking is gone. what a difference on shifting, engine, etc. totally new truck. 

what my point is, tuning can fix the clunks. the way GM has programmed these trucks is asinine. too many up shifts to quick, constant lugging, wanting to increase fuel economy to gov regulations. i dont think its setup correctly/synchronized correctly with tranny and engine setpoints. 

but hey, im not an engineer. 

 

30k miles. my warranty is up in 2 months anyway. 

You have the 8 speed? Last I heard nobody could tune an eight speed, well I know you can send off your ECM and have it swapped but I’m talking as is factory tuned.

roadkill5.3 Enthusiast

roadkill5.3

Posted
Posted (edited)
23 minutes ago, Chad2815 said:

You have the 8 speed? Last I heard nobody could tune an eight speed, well I know you can send off your ECM and have it swapped but I’m talking as is factory tuned.

6 speed

didnt know they had 8 speeds in 2014's...you might want to update your signature, and post more clearly what tranny your talking about in the original post, you  may have some better results ?

i doubt you have a crank issue...that would be the final step, but its most likely the gm parameters in how the tranny shifts, as i said above, i have 0 clunks now with my 6 speed after my tune. its butter. 

hasnt the 8 speeds always shifted like ****** and had more problems than the 6's?

tuning might be your only way out, or going to a different brand truck. 

 

goodluck

Edited by Jgreen2193
lucas287 Enthusiast

lucas287

Posted
Posted
On 8/30/2020 at 12:42 PM, Chad2815 said:

You have the 8 speed? Last I heard nobody could tune an eight speed, well I know you can send off your ECM and have it swapped but I’m talking as is factory tuned.

Do you have a 2017 Denali 8 speed? It can be tuned, just costs a bit more than the 15-16's. But yeah factory GM tuning on the 8L90 is garbage. There are many contributing factors to the clunkiness (in my opinion and experience)

 

1. The trans tune sucks all around. Primarily the TCC lockup schedule. 

2. Driver demand settings make transitions from light throttle to zero throttle abrupt. 

3. The 6.2 has zero cam ****** until .14g cylinder airmass. 

 

These three areas are big contributors to the poor driveability of the 6.2/8 speed. 

Chad2815 Enthusiast

Chad2815

Posted
  • Author
Posted

Yeah I have the 6.2/ 8 speed. Mine clunks but not every time, I was more posting that article so everyone knew not just complaining about mine. I would like to find a place that could tune it but its great WOT and 90 percent of the time, just when slowing down the clunk has started for mine. I have 44,000 miles, also makes a

loud clunk when I go from Drive to Reverse but again, thats just life with these trucks. Just thought I would share what I came across while doing research.

Z45 Senior Enthusiast

Z45

Posted
Posted (edited)

I have a 2017 Sierra Denali 6.2L / 8-sp. # yrs and about 35,000 miles (3 yrs old , original owner) and I never experience a clunk going from  drive to reverse.   I can't ever recall any down shift clunks at all ever.  Sometimes when driving real slow after cold start it will shift hard from 1st to 2nd but that typically occurs at 5mpg and only when I barely have any pressure on the gas pedal, just crawling along.  Live by the lake shore so I often just take in the scenery leaving home. 

 

PS - I had the ATF changed over to AMSOIL 2.5 yrs ago at about 10,000 miles more or less. .

Edited by elcamino

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