TSB Seems To Fix 8-Speed Automatic GM Transmission Problems1,791
We’ve covered the problems of the eight-speed GM transmission on numerous occasions. In fact, we cover a class action lawsuit brought against GM back in April, complaints from owners, and even a recommendation that GM replace the eight-speed altogether with a new unit as quickly as possible. Now, GM Authority has learned that there’s a new fix that seems to be alleviating the eight-speed’s shifting woes outright.
As of July 8th, 2019, GM began using a new type of Mobil 1 automatic transmission fluid for the troublesome transmissions. Customers that complain of shuddering and harsh shifting characteristics in the 8-speed GM transmissions are recommended for a trans fluid flush. As of August 7th, GM dealers should also be flushing all potentially affected new vehicles on the lot.
According to TSB (Technical Service Bulletin) 18-NA-355, the latest update addresses “torque converter clutch (TCC) shudder conditions on 8L45 and 8L90” eight-speed automatic transmissions, RPO codes M5N, M5T, M5U, and M5X. Affected vehicles include Chevrolet, GMC and Cadillac vehicles, as follows.
- 2015 – 2018 Chevrolet Silverado 1500
- 2015 – 2019 Chevrolet Corvette
- 2016 – 2019 Chevrolet Camaro
- 2017 – 2019 Chevrolet Colorado
- 2015 – 2017 GMC Yukon
- 2015 – 2018 GMC Sierra 1500
- 2017 – 2019 GMC Canyon
- 2015 – 2017 Cadillac Escalade
- 2016 – 2018 Cadillac CT6
- 2016 – 2019 Cadillac ATS
- 2016 – 2019 Cadillac ATS-V
- 2016 – 2019 Cadillac CTS (excluding V-Sport models)
- 2016-2019 Cadillac CTS-V
The issues with the 8-speed GM transmission are two-fold. First, some customers report the transmission shuddering frequently. Secondly, the shifts are very harsh between first to second, and then second down to first, especially when accelerating and the transmission is upshifting or decelerating and the transmission is downshifting. These conditions are most commonly observed under light and medium throttle applications, and as often during full throttle applications.
However, a new fluid flush appears to fix the issues, with some customers beginning to report a dramatic change in shift quality after swapping out the old juice. If the flush doesn’t fix the issue, the next step may be to replace the torque converter, which could be glazed.
The issue seems to stem from “moisture content in the transmission fluid.” As such, the old GM transmission liquid is swapped for new Mobil 1 Synthetic LV ATF HP fluid. Driving the vehicle for about a week or so improves shift quality even further as the new fluid cleans things up inside the transmission and the adaptive shift algorithms relearn various parameters.
This is obviously a big deal for owners struggling with their vehicle’s eight-speed. Hopefully the new fluid swap will provide a lasting fix.
Have you experienced shuddering and harsh shifts with your eight-speed GM transmission? Have you gone in for a fluid-swap fix? Let us know your experiences by posting in the comments section, and don’t forget to subscribe to GM Authority for 24/7 GM news coverage.
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How many quarts does the transmission pan hold? Got charged $110 for fluid.
A drain and refill is about 5-6 quarts. A complete flush and refill would be about 11 quarts. When mine was flushed with the new Mobil 1 fluid they just have 20 listed on the receipt. Mine is a 2017 GMC Canyon 3.6 ltr. w/8 speed.
Does the fluid have to be Mobil1 discussed above? Driven less than 300 miles since service. Would it cause problems that quick? Do I need to flush with Mobil1? Tried to do preventive maintenance and created a problem…..
No, i used the fluid of my choice which the dealer payed for Amsoil. It was a complete flush
Can’t believe the transmissions are so sensitive to fluid exchange. Hopefully it will make it back to dealer. Ofcourse this happens while out of town.
They can be. I heard it from Eric the car Guy on YouTube. He used to be a Honda Tech, and says with Honda’s, to only use the Honda fluid, because others caused problems. I guess in that Scenario the Honda had more additives in it or something who knows. So, I’m sure the same concept could apply here. As for the fluids, I’ve heard of people having zero issues with the regular GM fluid. I’ve heard Mobil fixes it if there’s an issue. I’ve also heard Mobil didn’t do anything. Been on this forum for about a year now. Amsoil is supposed to be really good, so far though.
Thanks, Dane. Hopefully it’s not damaged.
The trans flush is one of the main fixes….the fluid chevy and gm now use is the fluid they say is the fix…..I had mine done this past July and after I checked it was the Mobile 1 type they now recommended….
If your vehicle is older then a year it probably does not have the correct fluid and they are not changing them on the lots before selling..
So you need to request a transmission flush now to ensure it has the right fluid…dont let the dealer say anything less…
I believe the fluid had something to do with the thickness or maybe heat.. the correct type is part of this thread and can be googled
Thanks Geoff. Unbelievable that it’s that sensitive. Person before me must have had it serviced with correct fluid. I have no service records so wanted to have it done for routine maintenance. Hopefully nothing is damaged…..
Yep they changed the fluid I believe early part of this year.. may or June.
Mobil 1 Synthetic LV ATF HP is the new stuff… I believe HP was key.. but either way should be done with that at least…doesn’t fix it all tho
Good luck.. I have a 2015 silverado 1500 ltz 40k miles and will prob dump it when the ford 2021 superduty comes out….although Ford 10 speed has its own issues I think they are far less.
And I only have 2 yrs on my extended warranty
SD doesn’t get the 10 spd as far as I’m aware.
The new 2021 F250 with the 7.3 gas and the diesel is 10 speed.
Got the flush on my 2020 colorado. 400 miles later still doing same thing with new symptoms and I think the vibration sound is getting worst. Under 1600 miles on truck. Have to get it back in the shop!
Have 2019 v6 with new body style n its had trans fluid changed n 2 torque converters ..under 21k miles…same shudder n now jerking shifting…GM engineers sent to shop..not fixed yet..WTH????
I HAVE 6 SPEED TRANS…WHAT’S NEXT
I had a the shutter and harsh shifting problem on my 2016 Yukon Danali. Noticed it while travelling at 35 mph, and higher speeds. Harsh shifting occurred while initially shifting into gear or after stopping. In fall of 2019 transmission fluid was flushed and the problem was corrected so I thought. Within a few months the problems where back. Just got the torque converter replaced . Shutter is gone. However I am now experiencing an issue when the car is started. where I am getting action required messages to put windows up and down, radio
Turns on and the car stalls out. I disconnected and reconnected the negative battery terminal and the problem went away
However after one day and long the problem is back. Anyone else having this issue??
Cadillac Ct6–2016–47,000 miles–bought used from Cadillac Dealer–with 44,000 –(in another state–3 hours away)–bucking and trembling at low speeds–getting progressively worse–feels like running over mild rumble strips–took it to my non dealer mechanic who has done my cars for years–he tested it and said I should take it to dealer–might be covered under powertrain warranty–advised by local GM dealer that they would have to perform diagnostic test–$189–at my expense-if it turned out not to be covered–I bit the bullet–and it turned out it was covered–bulletin 18-na-355–triple drain and fill –seems fine now–but that’s just a few days ago–Question?–If GM knew this was a problem–why didn’t they have a recall?–all in all cost me 3 days of time–having people drive me back and forth to dealer–what a pain–
I ave a 2017 Sierra with the 8speed. My problems are shifting between 1 and 2nd ,downshifting 2nd to 1st. They flushed the fluid and it seemed to help but started doing it again. I took it back and they said it was because I was driving in auto 4wd. It was still doing it and they replaced the torque converter. I picked it up and it was shuddering real bad, I took it right back and they rebuilt the transmission. However it still does it. I don’t know what the next step is. It only has 41k miles on it. Thinking of trading it off.
Seems pretty much like they’ve done a lot to it mechanically. There may be something wrong with whatever they used for the rebuild, but I don’t know. The other main things to look at may be how GM has these vehicles programmed, or solenoid, valve body, etc. I don’t know what they replaced. I begging to see some truth in them just saying, it’s how they are. I’ve seen online where many people either bought a tune from a company like Trifecta, or paid a shop(not a GM dealer) to put a custom tune on the power train.
I recently purchased a 2015 escalate ESV I auto matically thought transmission was bad because harsh shifting.long story shorts took it to dealer they new about the issue already they did a double flush with a different fluid upgraded and now it’s perfect
2015 doesn’t have a 8spd.
Just purchased a 2017 GMC Sierra 1500 Denali 6.2 and noticed a couple weeks off the lot that it was shifting hard between 1-2. It is definitely more pronounced when the engine is cold and just pulling out of the parking lot. It’s as if the transmission drops down and kicks forward. Brought it into the dealership 4 times to have it looked at. New valve body, transmission flush, transmission harness, and update of transmission to re-learn driving habits but still having the same problems. Have a case open with GMC about it but does anyone have any recommendations as to what I should do? I’m getting ready to spend $4k to register and tag it and not looking forward to it due to the unknowns. Please help!
I’m sorry, my advice would be NOT to spend $4K on your vehicle. You won’t find too many people on this forum that have had their GM 8speed transmission serviced and it has remained problem-free. It’s a dud transmission that GM has no idea how to remedy.
That is disappointing. GMC wouldn’t be able to help in any way?
Tanner I have same vehicle you have…done all the run around at the dealer…it has 63000 on it now…either live with it or dump it…GM is fighting the class action suit tooth and nail…doesn’t seem theres going to be a solution…..
Very frustrating as my truck has 39k miles on it. Waiting on an answer from GM and then will go from there.
Dump it ! 2019 Silverado 10,000 miles dealer service operating as designed and GM consumer ticket open . Which doesn’t resolve anything .
I have a 2015 Silverado with the problemed 8 speed
I have a 2013 chevy avlanche with 158000 miles trans is shuttering and at red lights goes into neutral. 2 wheel drive truck. Any help
Dave that avlanche has the older 6 speed hydra matic. The fixes on this thread are for the 8 speed and probably won’t apply to your case.