TSB Seems To Fix 8-Speed Automatic GM Transmission Problems
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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.
Chevrolet
- 2015 – 2018 Chevrolet Silverado 1500
- 2015 – 2019 Chevrolet Corvette
- 2016 – 2019 Chevrolet Camaro
- 2017 – 2019 Chevrolet Colorado
GMC
- 2015 – 2017 GMC Yukon
- 2015 – 2018 GMC Sierra 1500
- 2017 – 2019 GMC Canyon
Cadillac
- 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.
Ending week 3 with my truck still in the shop. Either my dealer is being through or I am lucky enough (unlucky?) that problems persisted in their test drives. Started with a flush(worked for a few miles), then a back-ordered valve body (did not solve the problem). Now I am advised GM has instructed them to pull the transmission. So they will now rebuild or replace the transmission. I wish i could force them to do the latter.
For me this started at 24000 miles on a 2018 Sierra 6.2L. No problems or even hard shifts to complain of since new. Suddenly, the shudder started, followed by no response from a full stop either at a drive through or intersection.
I have heard that the transmission fill tube and dipstick from a 2018 Camaro 6.2 8 speed will fit in my 2018 Silverado High country 6.2 8 speed can anyone confirm and have the correct GM part numbers for the transmission fill tube and dipstick?
I don’t understand why they felt it was not need on the truck but was on the car?
I have a 2017 rs camaro it has no dip stick i thought all these were sealed transmissions
That’s a good question my friend, i put a B&M on my 2017 High Country 6.2L. $200 for a dipstick is expensive when they should come from factory with them.
I agree, I would love to maintain the factory warranty which someone posted has been increased to 120k miles, but I’m in south Florida and am thinking with 12K on my 2018 I will be long out of warranty before it completely shits the bed. So I’m considering the thermostat bypass mod as well as dropping the pan and changing the filter and oil to the Mobil blue label. I would prefer to have the dealer do the flush first but my dealer has not been very cooperative, I may go to the GMC dealer and see if they will do it.
Hello,
I have had my 2016 Yukon Denali back for a week now from my dealer in South Florida, Vera GMC in Hollywood. They performed the Transmission Flush, Filter, Temperature Sensor/Harness and reprogram. This was covered under warranty/special warranty. They had the truck for 2 days but the service takes about 4-5 hours total. Truck is running well, so far. They did assure me that this is covered for 10 years/120000. Hope this fixes all this.
Lenny
2016 GMC Yukon Denali 58800
Its very simply the fix is to replace the trany. But chevy wont do it. they will waste hundreds of thousands before they need to spend millions to replace them.
Gm always does things ass backwards, I’m so disgusted with Canyon I wish someone would steal it, I hate this transmission
Replace them with what another 8-speed? They never figured out the defect so replacement won’t fix this. It’s a bad design.
I just purchased a pre owned 2018 Yukon Denali a week ago and just noticed the pause then he’d shift when I go from Reverse to drive.
I have a 2020 Canyon experiencing the same transmission issues with 5K miles. Poor design.
It’s horrible, I’m gonna buy a Toyota, gm will never learn
Years ago GM came out with the metric 200 transmission they put in hundreds of thousands of cars and it was a piece of junk now they’re doing the same thing with this piece of garbage, gmc Garbage motor company, Professional grade you Gotta be kidding me
My 2016 gmc yukon denali (50K miles) has had this problem – shuddering especially at 30/40 and over 60 miles per hr. I also experience a hard shift/thump into gear when initially starting to move either forward or reverse. The oil was replaced and it did appear to fix the problem. However with in a few months it was back again. The GMC service dealer is now going to replace the the torque converter – under warranty.
Will GM ever Run out of people to screw
I have a 2019 Silverado 8-speed. Shuddered at 5k miles, took back several times, got the fluid flush, no help. Went to GM tried Lemon law, GM will not budge. I have 21k on it now. It shudders all the time now, not just at 1000-2000 rpm. If indeed what folks say “It is not all of them” Then why won’t they fix. Put in new transmissions, something. I can’t wait to dump this thing, every time I drive it, it is a constent reminder of the screwing I took
Had a 2017 Silverado 5 speed. Had the same problems as everyone else. First time, could not duplicate. Second time, transmission flush. Third time, service manager said tech was driving when truck went to limp mode. Said transmission overheated. Drain and flush and new torque converter., filters and relief (?) valve. Got it back, drove good for about three months. Then started shuddering and hard shift again. No help from the dealership. All the time this is going on, my salesman, who is also a personal friend, said GM knows about the problem, but is doing nothing about it. A good friend talked me into checking with a GM dealer he has been doing business with for many years. So, I traded my Silverado for a 2019 GMC Sierra X31. Truck has been great, until today. Began hard downshift when coming to a stop. And I do mean hard. Needless to say, I’m pissed. Have a trip coming up in four days and I will be towing a 20 foot trailer with two trikes on board. This trip has already been cancelled once due to COVID. We don’t want to cancel again.
Here’s a good question for every flush that’s done what’s not saying the machine isn’t contaminated with fluid from it’s past flushes and going into the next job?
This is ironic. I have a 2016 Silverado High Country (purchased at 30K) and is my first pickup/Chevy. Had no context to compare and noticed the issue almost immediately… As most have commented, initial shift from park to reverse, between 900 and 2000rpm (accelerating and decelerating slowly), and same when driving down a steep slope. Assumed it was a “pick-up” truck thing. I’m at 45K now and took it to dealership because it feels like it’s getting worse. To the point that I get anxious driving (tensing up anticipating the jerking/jumping like I’m about to get hit). They told me the transmission fluid needed changing and this is covered under Power Train Warranty. Also talked about running $150 diagnostic. I feel like they are trying to get over on me. Should I be paying anything for a problem they are aware of? Or is this a recall?
I should quantify my response. My truck is in literally today (09/21/2020). So this is a 4 year old vehicle and this is still a problem with even 2020 models?! This 8s shameful. I thought thisc was an old thread.
My 2019 canyon lease (7000 miles)was dropped off on 9-10-20 to the service department because of shuddering at all different speeds. After having to get with Gm engineers, so they told me, I was notified today(9-22-20) that they will be replacing the torque converter. Hope this fixes the problem.
Good thing you’re in a least and you didn’t buy. There is no cure for this 8-speed. It’s defective.
My 2017 Sierra with 30,000 miles has had problems shifting first to second and back to first….sometimes feels like it is being rear ended….in shop now for fifth time….last was entire month of February and no fix…this time went in on 8-4-20 and still in 7 weeks today…was told new tranny was needed….new tranny came in and sat on shop floor for 3 weeks waiting for cooler lines and other parts to come in….dealer just called and said, upon inspection, tranny is wrong one for my truck….so I’m on back order and no telling when new one will be delivered…
I have 2018 GMC Sierra Denali with the 6.2 and my truck is in the shop for the 3rd time now over the past 4 weeks. The truck now has 40K miles on it.
I initially felt the shudder that gradually got worse until my check engine light came on so I took it in. The dealership performed the transmission flush and it took about a week for them to get to. The truck still didn’t drive normal and the shudder eventually came back worse than before. This time the transmission was shifting hard and seemed to be stuck in a high gear when I tried to accelerate from a stop ( high RPM and very little pull). So I took the truck back again and this time they told me the torque converter was bad so they needed to replace it. After another week, I got the truck back with the new torque converter and drove it to work. This time the check engine light came on after approximately 20 miles of driving. This time when slowing down the truck downshifted so hard I was worried there was some serious damage. Then when I tried to accelerate from the stoplight the RPM’s got up to 3 or 4K before the truck started moving.
Took the truck in again and they are telling me the Transmission Control Module is giving incorrect voltage readings so they will have to order the part. Probably another week in the shop.
Has anyone else gone through this after the torque converter replacement?
I feel like the dealership is patching this together to get past my warranty.
Similar situation. My truck is in the shop now and has been in the shop for the past month to the day. Flushed, still hard shifting. Valve body, still having shudder or something (maybe kudos to my dealer, seems like they are testing thoroughly). Was told that GM recommended a complete rebuild. Parts were back-ordered through the process which leads me to now. I am told they have everything and should be done tomorrow. That is if the test drive goes ok. I have a 2018 Sierra SLT 6.2, 8 speed, 24,500 miles
Fail again! Now I am told a new transmission is on order. I am now just over one month without my truck. Hope this works. Won’t shock me if it is short term and I get the runaround next time. I would trade but I don’t t want the added debt. 🙁
Would like to know results and what they did
I read all of the comments and we are having the same issues with our 2017 Yukon Denali XL.
Dealer tried to tell us that they checked with GMC and it was perfectly normal…..bulls@#t
Waiting to here from GMC senior advisor about moving forward