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6 Speed Transmission Clunk Downshift

JacobC1983
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Grumpy Bear
Grumpy Bear

I'll be sure to tell my truck's 6L80E transmission about this. It has been picture perfect for nearly 60,000 miles. Evidently it doesn't know that it spoiling the others awful reputation.  

Mike GMC
Mike GMC

I believe the "mine is fine" posts are in response to the equally useless, "they all suck" posts.   That said, have you done a fluid change?  What does the fluid look like?  How is the fluid

Grumpy Bear
Grumpy Bear

Problems with threads like this. 10 guys who never met each other with 10 different situations assuming 10 different assumptions are creating the exact same issue. Make a guys head hurt....  

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NorthEast Enthusiast

NorthEast

Posted
Posted

I'll bring it up again at my next service visit, it does not pass as "normal driving characteristics".

Running it in L5 all the time makes it 90 percent better.  It also disables V4 mode and the truck still gets over 20mpg.  

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Shane Kelly New Member

Shane Kelly

Posted
Posted

I just bought a '16 with 12,000 miles on it and it's clunks (hear&feel) while downshifting in most gears.  I stuck my edge tuner in there and tried a few different tunes but nothing helped.  I noticed the converter locks up in 1st gear and stays locked during every upshift while accelerating slowly.  When downshifting the converter stays locked until 2nd gear I believe.  The clunking is the worst from 4-3 and 3-2.  I'm pretty sure all of the clunking is because of the torque converter.  I'm use to my 4l60e and 4l80e only locking up after a set speed in 3rd and 4th gears.  There is no way it's normal for the converter to lockup when it does..

Mozzer Enthusiast

Mozzer

Posted
Posted
I just bought a '16 with 12,000 miles on it and it's clunks (hear&feel) while downshifting in most gears.  I stuck my edge tuner in there and tried a few different tunes but nothing helped.  I noticed the converter locks up in 1st gear and stays locked during every upshift while accelerating slowly.  When downshifting the converter stays locked until 2nd gear I believe.  The clunking is the worst from 4-3 and 3-2.  I'm pretty sure all of the clunking is because of the torque converter.  I'm use to my 4l60e and 4l80e only locking up after a set speed in 3rd and 4th gears.  There is no way it's normal for the converter to lockup when it does..
That's exactly the symptoms I have with mine, torque converter feels like it isn't unlocking at light throttle shifts. Any way to convince the dealer this is not 'normal operation'?

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Shane Kelly New Member

Shane Kelly

Posted
Posted

I hooked up my hptuners and experimented by disabling torque converter lockup.  As I figured, it shifted beautifully and overall felt so much better!  You can definitely feel the torque management a lot more between shifts though

Sierra Dan Senior Enthusiast

Sierra Dan

Posted
Posted

The 4L60E was plagued with issues.

I had every one of them fail in various ways on my trucks ranging from 1994-2005

nluchau Enthusiast

nluchau

Posted
Posted

Are you guys experiencing what I am specifically?  

When I go above 40 and coast or easy brake to a stop.  When its doing the 4-3, 3-2, 2-1 downshifts I feel a jerk or a tie up sensation and a release when it downshifts.  I also see the RPM's bump up (which is what I should see).  The jerks or bumps or tie up sensation feeling has been occurring since new on my 2016 5.3 6 speed.  I've brought this up quite a bit here but there tends to be no fix insight.  The dealer replaced valve body and TCM and has reset taps but nothing has fixed it.  

Mozzer Enthusiast

Mozzer

Posted
Posted

Mine is more noticeable when it changes down under very light acceleration, also has the symptoms you describe if I change down manually while coasting.

Best description I've seen is earlier in this thread, clutches / torque converter not disengaging/slipping.


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Mozzer Enthusiast

Mozzer

Posted
Posted

Mine is more noticeable when it changes down under very light acceleration, also has the symptoms you describe if I change down manually while coasting.

Best description I've seen is earlier in this thread, clutches / torque converter not disengaging/slipping.


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nluchau Enthusiast

nluchau

Posted
Posted (edited)

I just found this online:  

https://atracom.blob.core.windows.net/webinars/gm/6l50_80_90_updates.pdf

 

6L80 Intermittent Harsh Downshift, Chuggle or Shudder During Deceleration 5.3L Tahoe, Suburban, C/K Trucks Customer complaint may be harsh forced downshifts or the chuggle/shudder during a coast down intermittently. This is considered “Normal” with this powertrain package. It is a self test for the O2 sensors. Test runs with the vehicle speed above 45 MPH (72 kph) in 6th gear with the TCC applied. The ECM drives the fuel system rich and then into deceleration fuel cutoff mode (shutting the injectors off) to check the system. Test will end during the deceleration and fuel is restored. (This typically causes the Shudder/Chuggle shift feel in the vehicle). Aggressive throttle response during this system check mode will cause the vehicle to have a “Harsh” downshift (this happens because the TCC remains applied during the test). If the test runs while in 5th gear, the TCC will not be applied and the complaint will not likely occur. Note: The test is designed to occur one time per key cycle, but can run up to 10 times if aborted due to throttle input.

 

Mine isn't intermittent as it does it all the time, it doesn't go away in M5.  

Edited by nluchau
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njk4o5 Enthusiast

njk4o5

Posted
Posted

I had brought mine in probably 10 times for the sh!tty transmission and they replaced different internals every time until I finally flipped out and made them get me a complete new trans. that was at 96k miles right before my powertrain was up. The "new" trans is somewhat better but the truck is still not peppy at all and it has no idea what gear to be in when you let off the gas pedal and then get back on it. At least it doesn't downshift so hard your drink spills...for now

 

Chevy missed the mark with these trucks.  Good looks and good interior but the drivetrain is trash. I surely wont be getting another anytime soon. I try and tell everyone who is thinking of buying a new chevy to drive it and see how terrible the trans is.

  • Like 1
nluchau Enthusiast

nluchau

Posted
Posted
3 minutes ago, njk4o5 said:

I had brought mine in probably 10 times for the sh!tty transmission and they replaced different internals every time until I finally flipped out and made them get me a complete new trans. that was at 96k miles right before my powertrain was up. The "new" trans is somewhat better but the truck is still not peppy at all and it has no idea what gear to be in when you let off the gas pedal and then get back on it. At least it doesn't downshift so hard your drink spills...for now

 

Chevy missed the mark with these trucks.  Good looks and good interior but the drivetrain is trash. I surely wont be getting another anytime soon. I try and tell everyone who is thinking of buying a new chevy to drive it and see how terrible the trans is.

Good to hear from you again njk4o5!  Mine isn't downshifting where I'll spill something.  Its just annoying as heck still.  

thekevin Enthusiast

thekevin

Posted
Posted

My 2018 will clunk in the same spot pretty much every day. On the 4 lane to my house there is about a half mile down hill coast, then a mile long uphill and right at the top is my exit that is also uphill that comes to a stop sign. Pretty much every day when slowing for the stop sign it clunks really hard on the 2 - 1 shift. I have a Range AFM disabler.


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NorthEast Enthusiast

NorthEast

Posted
Posted (edited)

I experimented this week after some success with L5 driving.  

 

L5 eliminated:

V4 mode

35 to 39mph shudders

80 to 90 percent of clunking

 

Then I tried Tow Haul mode.  The first few days of driving resulted in some gruff driving characteristics (holding onto gears for a few seconds more than necessary before upshifting)

 

After the transmission "learned" my driving style, 

it is better but still hangs on to gears for too long

 

L5 with Tow/Haul eliminated:

Early upshifting 

Gear hunting 

Clunking

The usual V4 mode demerits

 

In summary, running L4 under 50mph and L5 for everything else solved everything.  T/H was too rough.  The truck is a breeze to drive now, L4 improved throttle response as well.  

Edited by NorthEast
  • Like 1
njk4o5 Enthusiast

njk4o5

Posted
Posted
On ‎1‎/‎13‎/‎2019 at 4:55 PM, NorthEast said:

I experimented this week after some success with L5 driving.  

 

L5 eliminated:

V4 mode

35 to 39mph shudders

80 to 90 percent of clunking

 

Then I tried Tow Haul mode.  The first few days of driving resulted in some gruff driving characteristics (holding onto gears for a few seconds more than necessary before upshifting)

 

After the transmission "learned" my driving style, 

it is awesome

 

L5 with Tow/Haul eliminated:

Early upshifting 

Gear hunting 

Clunking

The usual V4 mode demerits

 

L5 with Tow/Haul Maintained:

20+ mpg in mixed driving

 

In summary, this setup made my truck normal (not a shitbox).  In suburban/semi-urban driving, the gear-holding prevents unnecessary upshifting. Staying in lower gears gives significantly better throttle response, even with small inputs.  No more gear jumping when getting on and off the gas.

Highway driving between 55 to 70 is a little louder because it revs at a constant 2k, but still returns good fuel economy. 

I think these truck come from the factory in some form of a SuperEco mode to score good EPA results.  L5 plus T/H brings them back to reality.  

good to know, im going to try this on my way home from work tonight. good write up thanks

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