8 speed issue

Scooter Scott · July 16, 2018

I think my 8 spd is getting worse. Need to take it in soon.

Bigmac · July 18, 2018

Had a 2017 Max tow 6.2 8 speed that tows my rv. It started a shudder when pulling from a stop when towing. Worse when hot. No problem when it shifts in the higher gears. Feels like tq is pulsating. It definitely is a tq problem. Dealer flushed twice and replaced the converter twice but continued. G M said no problem but we all know otherwise. Had a chance to sell it and purchase the exact twin only a 2018 for very minimal difference ( long story). Guess what - does the exact same. The shudder is very apparent and severe when hot. Only 2000 miles on it but I know to live with it. Love the truck otherwise. The shifting is much better as this was built in May so hopefully has the latest trans updates. That’s my story ??

gtbigup01 · July 28, 2018

On 7/3/2018 at 4:35 PM, EDL said:

Ugh, you guys are scaring me. I started having the transmission surge at vehicle start up yesterday, but someone posted the TSB that it is normal and no repair required, and today I did like someone suggested and let it idle for about 30 seconds in park before shutting it down. It never surged at start up once, so the idling thing appears to work.

I do have the thunk when coming to a stop as it downshifts from 2nd to 1st. Today a couple times it thunked hard after coasting then getting back on then throttle at low speed (like coming to a stop light, but not completely stopping and adding a little throttle to move up another 10 feet). It felt like when you have a really bad u-joint, or like there's a lot of slack or lash in the gear mesh. Press the pedal and it spins up to take up the slack and then thunk when everything engages. It only did it a couple times, but that's something else to keep my eye on.

God, I hope this thing doesn't turn out to be a headache. I haven't had a Chevy vehicle since 2001 and I so love everything else about the truck, please, please, please don't become the reason for me to leave Chevy again....amen. :-)

Bro my 2017 Sierra did that the first week I took it home. 13 months and 35K later it is a lot better but it still exists. You will soon discover there's no fix from the factory for it. Just like you explained, the issue mostly occurs while crawling like in stop and go traffic. Moderately accelerating it's fine, as soon as you get into bumper to bumper traffic you will get the "thunk". Software update did nothing to fix mine.

I drive 112 miles daily (round trip) just for work, so in 3 yrs of ownership is well past the mileage I usually trade a vehicle in. Other than this issue (non-issue according to GM), with my first GM product, i haven't had anything else go wrong. Still, not sure I'll be a repeat customer. In 2 yrs we will see.

EDL · July 31, 2018

Now that I'm approaching 2000 miles on her, I've gotten kind of used to it. I still sometimes forget to let it idle a bit so next engine start it thunks and lurches.

Still getting the thunk in general ever now and then while driving. It'll happen at speed if I let off the gas and then get back on it, so it seems to be related mostly to letting off then applying throttle again, regardless of speed.

As for the vibrating and rumbling at highway speed, and the just general vibrating in the steering wheel, I've noticed it's never the same. Some days (especially on a cool morning) it tends to ride pretty nice, but by afternoon after it's sat out in the sun, the ride home has a lot more vibrations. I don't know that it's solely due to the transmission, I think it's a combination of tires/wheels, drive shaft and maybe the transmission.

I've had an extremely busy month (was down for a week a couple weeks ago with a kidney stone) and haven't had time to get it to the dealer to see about getting the flush done and road force balance the wheels (and get my fob reprogrammed). I'll ask about the drive shaft, but I suspect I'll just end up paying the $95 to have it trued and balanced at the local drive line shop (which I have no issue with, at least it will eliminate that one variable). Then we'll see where things are.

I think the clunky trans is just going to be there and that's that.

I did finally romp on it good a couple times, man, that 6.2 has some get up and go once the tach passes about 3500.

SkiDooNick700 · August 1, 2018

Lately my entire truck noticeably rocks like a ship in hurricane (ok, a little exaggeration) when I shift from Park to Drive on a cold start. I always remote start and truck runs for at least a minute or so - to the point where the RPMs are down to around 600 - so it's not like it's still choking at 1100RPM and I'm dropping it into Drive.

What is the thought behind idling for 30 seconds before shutting down? Sorry if I missed the explanation...

Pearl2017 · August 1, 2018

You guys with the clunking i feel your pain. Mine just started having the issue a week ago at 26K and IMO it is all due to the TCC. the old timer lockup TCC was either on or off and it had heavy buffer springs to cushion the engagement shock and not much else to go wrong just a solenoid and a signal. And on the highway you knew you didn't want it cycling a lot or it could burn up and wear out.

The current tech is like balancing a coin on its edge, the TCC is constantly PWM - modulated and is designed to be almost always slipping a small amount until a large enough power demand is demanded for it to 99.9% lock. Along with the TCC modulation the cushioning springs were made much weaker as their job was supposed to be less drastic. So when the TCC is behaving badly the Thunking IMO is the TCC banging past the light springs to the stops. From what I have been reading this TCC balancing act can become unbalanced easily by things like a dirty MAF with errant reading or micron sized fluid contamination that is not caught in the filter or the TCC material itself wearing and becoming "Grabby". Fluid flushing, TC replacement and possibly PWM solenoid/valve if just off a bit or sticky. On my truck today while scanning on hwy with cruise enabled. If i go 66 mph i get all the symptoms and a slipping TCC I poke the CC to 67 mph and the TTC locks up and all symptoms go away. ...This TCC system is just EVIL! maybe i can post a screen cap of the scan later if there is interest.

samckitt · August 23, 2018

On 7/14/2018 at 12:57 PM, J_Mas6.2 said:

my 15 did this, took it in and they changed the Torque Converter. Solved the issue

I had the torque converter replaced too but still have the clunk & the shudder when I accelerate slight (without transmission downshift). They didnt say anything about the "Fast learn" though.