My 8-speed Auto Transmission is a Stumbling Drunk

Nasty · October 1, 2018

On 9/27/2018 at 5:28 PM, AgDoctor said:

Is there any possibility of swapping a 10 speed into our trucks?

Sent via Morse code

Iwould have to pass on that. Most of the issues are from thr 8spd. Just imagine the 10

InVision · October 1, 2018

On 9/27/2018 at 4:45 PM, mjm-1957 said:

The fluid change is only for TCC shudder.TSB 16-NA-175. It will do nothing for the horrible upshifts and downshifts.I am the transmission guy at a Buick GMC dealer and am very familiar with the M5U transmission. Garbage. The ten speed is light years ahead of the eight speed. I can't even begin to explain the amount of time I spend trying to make the eight speed at least driveable.I just did a flush for a shudder concern this morning on a 16 Yukon with 30,000 miles and am finishing up a complete transmission replacement on another 16 Yukon with 46,000 miles after it already had a convertor 18,000 miles ago.GM said don't even bother going inside on this one just replace it.Lets see how long this one lasts.

It turns out that TSB 16-NA-175 is only for 2015-2017 GM vehicles. And it is quite a procedure of flushing and draining with Mobil 1 Sen LV ATF Dexron HP. So not just replacing fluid and filter.

M

mjm-1957 · October 1, 2018

^{Check that bulletin again, was updated over the summer to include 2018Model year also.All of the eight speeds are involved and are nothing but a headache.}

Sir Dan · October 6, 2018

That title is so spot on! My 2016 5.3L 8 speed was very, very disappointing for the first 10,000 miles. It would slam down into 1st gear randomly at slow speeds and upshift into God knows what gear and lug the engine down, then downshift again. It made for a jerky unpredictable drive for sure. Putting it into M7 helped a bit and it went in for a software update that was great for 100 miles then back to sh!t. Honestly, the only thing that helps is putting miles on it. After the first 10K miles things got gradually better. It's still far from a refined, smooth shifter but at least it's tolerable now.

Edited October 6, 2018 by Sir Dan

MD11G200 · October 12, 2018

On 9/24/2018 at 3:18 PM, Pearl2017 said:

Go to a different dealer. There are a lot of threads about Fluid and filter change and TC replacements fixing the issues. Mine fully resolved with fluid and filter. I have V4 disabled, I find the constant switching in and out of V4 for a few hundred feet at a time more annoying than the 3 drops of gas i may saved leaving it on. WAYYY Smoother with it off.

I am curious, is it still WAYYY smoother?? did the same thing with the AFM V4 disalber and was good for 3-4 weeks, then back to sh!t. Fluid and a filter can't resolve an issue that is obviously intermittent and a TCM problem, I am not sure that everyone in here understands each others problem and unknowingly offers false resolutions, been to 3 dealers, had 2 TCM tunes and 1 flush, THIS IS A TCM problem and will require a TUNE to fix, changing the filter and flushing the fluid is for a shudder issue where transmission clutch material has made its way into the converter and causes a "weighted problem" kinda like a washing machine with an uneven load.

MD11G200 · October 12, 2018

On 9/27/2018 at 2:57 PM, Pearl2017 said:

There are many posts that describe the problems people are seeing. Having had the problem myself I can say it is correct to call it a chuggle or momentary vibration ...and it can be felt in the steering wheel as well as if a front wheel hit a small bump. Mine started out as random events then ~25k miles started to happen continuously. From everything I have read and my experience the issue is within the torque converter. There is a clutch that is meant to SLIP to maximize engine torque and save fuel. Once the Clutch begins to wear and/or the fluid begins to breakdown or become contaminated the operation of the TCC is no longer smooth. Changing the fluid can resolve the problem by restoring the spec needed to operate the system correctly. It is not always the only fix but just the first thing to try to resolve the problem. Second step is to replace torque convertor as it was defective or gone bad.

I will also add that having looked at the ECU using Hp-tuners after service they did update the operating system so it is not just the trans that is better. And the truck now drives and operates almost perfectly. All this they did without once lowering my expectations or telling me garbage function was normal. Find another dealer that has a good mechanic that keeps up on current GM fixes and they should fix it. Sounds like your existing dealer is lacking that good mechanic.

Are you saying you got the HP-tuners ECM tune and it fixed your problem? If not what exactly did your dealer do, i have been to 3 different ones now

Pearl2017 · October 15, 2018

MD11G200, Not saying hptuners fixes anything. But it does allow one to see what if any changes were made. The statement i made was that I could see that the dealer updated the operating system in my ECU and the engine output seems to display some positive benefits. Nothing i can see in the calibration values seems to have changed.

As far as shudders and rough shift I do think those are separate problems. IMO The Shudder is not as you said due to TCC friction material throwing the TC out of balance. The TC lockup clutch at part throttle operation is being commanded by a computer to be continuously slipping say 10% as example. For this level of control to be achieved the computer must have all its sensors and control valves calibrated initially and continue to remain within specific operating parameters. This control system is said to be a learning system meaning as components wear and change the computers algorithms update the calibration values to maintain harmony and balance. To complicate matters there are other programs that can intervene, Stabilitrack, Engine Braking and V4 DOD mode all working to upset the balance and our human perception of smooth operation. There is also a possible bad batch of TCC's that were installed leading to premature failure?

With the Flush and filter cleaning procedure it is my understanding that what is actually done is a complete reset of the system. To accomplish this you must start with absolutely clean slate (ATF). With the new fluid being virgin clean, the system can then begin a full reset. The reset is a series of software routines built in to the computer that cycles valves repeatedly to dislodge contaminants and thus clean the system. After the system is thoroughly cleaned calibration routines are run that dial in all the sensors and actuators preparing the system to begin the important job of processing then continuously integrating system variables to achieve designed functional performance targets over time.

The chuggle, vibration or rough shifting seen I don't believe can be "Tuned Out". I believe these are complex control algorithms based in the OS level of the control computers that need to be engineered/refined some more. The fact that the OS on my ECU was updated gives me some indication that GM is still engineering the monumental balancing act that is your engine/transmission drivetrain. And quality control of system hardware components is also absolutely critical to long term function.

Flush n filter,... Turn off V4... turn off engine braking... for me has worked wonders. If I have one of the faulty TCC.s I'll be knowing before the extended warranty expires. Good luck

InVision · October 16, 2018

ahh "Chuggle" is the term. The chugging at very low speed and RPM. Thanks !!

M

Spurshot · October 16, 2018

On ‎9‎/‎27‎/‎2018 at 5:28 PM, AgDoctor said:

Is there any possibility of swapping a 10 speed into our trucks?

Sent via Morse code

Possible, but likely incredibly complex and expensive. Probably a complete engine/trans package with ECM/TCM out of a 10 speed truck would be the most direct path. Not sure what a 10 speed would cost new. The 8 speed is about $4k new online, without TCM, harness, etc.. A new truck would be more economically viable.

Donstar · October 16, 2018

1 hour ago, Spurshot said:

Possible, but likely incredibly complex and expensive.

I agree that switching/upgrading transmissions in modern trucks is not be a viable option. Decades ago this was a popular modification and I'm surprised the idea doesn't appear more often on this forum. Adding two (or four) gears to any of our engines would be a popular modification if not so wrought with technical and costly hurdles!

InVision · January 12, 2019

Members - Going to take our 2018 Sierra Denali in for the "Stumbling Drunk" transmission issue. I can't seem to find the 2018 addition to TSB 16-NA-175. My friend took his 2016 in and the dealer not only drained and put new fluid in, but ended up replacing torque converter. He is SO HAPPY now :-). The dealer also mentioned that they put the wrong oil in the transmission. He stated that the part number for the fluid was off by one number what ever that means...

Would like to hear from anyone about there dealer experience before we brave ahead...

Thank You

M

mjm-1957 · January 12, 2019

16-NA-175 was updated again on 10/11/18, includes all 2015-2018 M5U transmissions in sierra and yukon and -2019 M5T in the Canyon and Colorado. They have also come out with yet another flush and fill procedure requiring 20 quarts of another updated HP fluid.We are waiting on the tools to convert our trans cooler flusher over to be able to perform this and also waiting on the new fluid.Seems to be in short supply at the present time. Time will tell if this provides any lasting repair. 75-80 % of my time is spent on these pieces of shit. I have never had a ten speed apart yet and they have been out two years already. The eight speeds were lined up for repair the minute they were released. GM should be ashamed of themselves....