2011 Z71 Avalanche shuddering under light acceleration.

[islandgrown83]

So the past few months I have noticed under light acceleration my Avy will shudder. It will start at speeds as low as 20mph and has done it as fast as 55mph. I have been told its one of 2 things. Keep in mind I only have 97,000 miles on my Avy.

First possibility is torque converter shudder.

Second possibility is AFM is causing it.

Has anyone else had any issue like mine?

UPDATE---- So my local service department said this is a very common issue with the AFM. When in V4 the engine is not well balanced because of the other 4 cylinders not being completely utilized other then warming. That with the combination of lower power causes the vibration when lightly pushing on the pedal trying to sustain speed while the AFM is active.

 

[strange]

I don't know if this is going to help you, but here is a problem I had and how I have "solved" it.  Well, at least it is not as noticeable as before...

I had a bit of a stumble at idle and when accelerating from a stop.  Not all time, just some times.  Not a huge stumble either, just enough to notice something is not quite right. 

What I do now is drive 90% of the time with the "Tow/Haul" engaged.  I get a more lively truck as the shift points are now raised a bit.  I'm sure the gas milage is suffering somewhat, but I did not purchase the Avalanche for it's great mileage.

Second, as I keep reading a about the AFM issues, I sometimes drive with the AFM locked out.  Not all the time, but probably about 40% of the time.  I just put the shifter into "M" (manual) mode and then toggle up to "Fifth" gear.  Now the truck will not slip into the sixth gear, but the AFM will also be locked out.  Or so I have read in the past...

I don't really notice any difference with the AFM locked out, but I do notice a big difference in the Tow/Haul on.  No more hunting for the next gear at a certain speed, and no more early shifting.  When I drive my wife's car, I tend to shift her 6 cylinder 5 speed manual gearbox at around 3500RPM.  It just seems happy there.  I feel the same way with the Avalanche.  It likes taking the RPM's up a bit before the next shift.

That stumble?  Well, it's still there sometimes.  But when I do move away from a stop, the truck seems to be smoother.  I don't know if others have found this.  As for your Torque Converter - sorry, I can't offer you anything there.

I would at least try locking out the AFM and seeing if you like the difference.  Nothing to loose...

Michael
   

 

[mac9427]

Hi, I have a 2011 w/50000k and it does the same thing.  I do what Michael does also, keep it out of 4 cylinder mode.  It has more bad side effects as well, as soon as mine come off warrantee I am getting the AFM programmed out.

 

[ezstriper]

my 11 does it as well, it seems to take a second to come out of V4 mode and that is what it seems to me is the cause, waiting on superchips now to do a tune for mine as they did not have my calibration on file so I can get rid of the AFM

 

[a745035]

I just bought a 2011 LTZ with 115k miles and mine has the same symptom, though I have trouble believing it's from the AFM system. With mine, V4 only activates if I'm completely off the gas and coasting, or just maintaining relatively slow speeds on flat roads with almost zero load. When displaying instant economy on the DIC, I can see it go back and forth from V4 to V8... and it goes back to V8 with almost no provocation. Regardless of whether or not I'm in tow/haul mode or in manual shift mode, I get the shake if I'm 1/4 to 1/3 or so into the gas pedal... more than enough to engage all 8 cylinders but not quite "authoritatively" enough to cause the transmission to downshift to the next lowest gear. RPM is also a factor... less likely the higher it is. The symptom is what I would describe as sort of a "flexing" shake... not high enough frequency to call it a "vibration." In the short time I've had this truck, it's been a maddening issue which was exacerbated just today while towing a light 5x10 landscaping trailer, or otherwise having any additional drivetrain load... such as with climbing long gradual hills. I found this thread through word searching "shudder." Hoping there are others that will give me a better idea as to what's really going on. Glad to have found THIS post! - Thanks.

**UPDATE**

Had Transmission diagnosed, then a full in-shop rebuild with all updates, including new Torque Converter. Completely resolved not only the drivetrain shuddering/slipping issues, but also the annoying momentary "grind" sound upon cold startup that SO MANY have reported across varying threads... initially thought to be the starter or the power steering pump. Turned out to be cavitation in the trans due to momentary lack of fluid flow. That grind symptom was WAY longer for me upon cold start due to my severe trans issue, but the sound is unmistakably the same. With the trans rebuild (only), that momentary cold start grind is 100% GONE. Hope this info helps someone.