issue Transmissions Issues/Problems

14silverado4.3 · March 8, 2017

I was towing a garden trailer with a 700-pound tractor in it in the lower mountains of TN, going about 60 mph downhill when the transmission suddenly went into 2nd gear! The rpm pegged out and the trailer almost jackknifed on me. I was in the trailering mode but have never experienced anything like this before. I immediately switched out of the trailer mode for safety. I believe the GM transmissions are totally unreliable in all modes of operation and there appear to be areas where the transmission does things that have not been programmed for it to do. It appears to just slide into gears that should not be expected whether it is an upshift or a downshift.

Grade Braking

Poffdaddy · March 8, 2017

I had a 2016 ltz double cab with 6.2 v8 and 8 speed transmission and now a 2017 ltz crew cab with 6.2 v8 and 8 speed transmission. Never had any of vibration issues or any issues at all after 3600 miles but transmission does a lot of issues that others have said 6 speed does. Never felt like it was in neutral but both trucks clunker in 1 to 2 shifts at low speeds sometimes very harshly. Took 2017 truck to dealer and they did quick learn tsb for harsh low speed shifts. It clunker first shift upon leaving parking lot. I now drive it in my or m7 anywhere but on interstate. It makes it better but not perfect. This is my first new pickup of any brand, well actually the 2016 was. I love the truck otherwise. Lots of power when it shifts properly. I didn't test drive other brands or have experience with pickups from other brands. I would have bought a tundra because of the toyota reputation for reliability as well as my own experience with toyota cars. The tundra doesn't get good ratings mainly because of the need for a major redesign. They of course get outstanding reviews for reliability and durability and it's hard to find a bad consumer review on a tundra other than the fact that it doesn't get great gas mileage. I should have went that route for the feeling of security. I definitely didn't want a dodge and I didn't want a pickup with a turbo v6. If you look at data on reliability between ford and gm pickups on both conumerous reports and jd edwards it's pretty much a tossup. Any real life experience out there between the two? I can say I probably won't buy another gm pickup and I will trade this one in on a tundraft whenever they get a redesign in 2018 or 2019. You can get a very nice tundra for the price of a mid range gm or ford also.

bderby66 · March 10, 2017

I have noticed the hard shifting at times. Just having conversations with gearheads, they attribute it to the change from 4-> 8 cylinders and 8->4 cylinder operation while driving. I may see that as contributing but not the end all answer. The clunk I hear sometimes sounds like it is coming front the rear end. Some of it I just decided is not anything broken...just very poor design from GM engineers. Kind of like the parking brake cable that hangs down below the axle on a Z71 4x4. Dummies!!! Yes....I will be thinking very hard and long about what brand truck I buy when the time comes for a new one.

My specific reason for posting here is to ask if anyone else is experiencing poor performance in cold temperatures from either their transmission or the front end drive train? I have been experiencing this issue since I bought the truck in September 2014. I have had it to the dealer a few times and they can never reproduce. If they drove it on a ~30 degree morning, and then hopped back in at 4PM when the temperature rose to ~50 degree's it would be a literally like night and day driving experience. At night after the temp rises it is like driving a Cadillac compared to the AM. It doesn't happen during spring summer and fall so urgency is questionable, Of course, if their isn't a computer code many dealer tech's can't troubleshoot these days to begin with.

When this issue occurs, the truck feels sluggish. It will down shift for more torque on the same hilly roads I drive everyday with ease. My fuel economy drops between 3 - 5 mpg. I feel like it is in the front end because the bumps in the road feel more harsh on the cold days when experiencing the issue. Because of the extra effort being transferred from the drive train to the rear wheels, it feels sort of like the front wheels are not rolling over the bumps in the road, they are being pushed into the bumps in the road (make sense?).This happens without my ever leaving 2WD mode, so it isn't the sticking armature issue disengaging from 4WD in the cold.

It is very frustrating. I am getting ready to try a different dealer but wanted to see what you all may have to say first.

Edited March 10, 2017 by bderby66

Ron.s · March 12, 2017

I had a 2016 ltz double cab with 6.2 v8 and 8 speed transmission and now a 2017 ltz crew cab with 6.2 v8 and 8 speed transmission. Never had any of vibration issues or any issues at all after 3600 miles but transmission does a lot of issues that others have said 6 speed does. Never felt like it was in neutral but both trucks clunker in 1 to 2 shifts at low speeds sometimes very harshly. Took 2017 truck to dealer and they did quick learn tsb for harsh low speed shifts. It clunker first shift upon leaving parking lot. I now drive it in my or m7 anywhere but on interstate. It makes it better but not perfect. This is my first new pickup of any brand, well actually the 2016 was. I love the truck otherwise. Lots of power when it shifts properly. I didn't test drive other brands or have experience with pickups from other brands. I would have bought a tundra because of the toyota reputation for reliability as well as my own experience with toyota cars. The tundra doesn't get good ratings mainly because of the need for a major redesign. They of course get outstanding reviews for reliability and durability and it's hard to find a bad consumer review on a tundra other than the fact that it doesn't get great gas mileage. I should have went that route for the feeling of security. I definitely didn't want a dodge and I didn't want a pickup with a turbo v6. If you look at data on reliability between ford and gm pickups on both conumerous reports and jd edwards it's pretty much a tossup. Any real life experience out there between the two? I can say I probably won't buy another gm pickup and I will trade this one in on a tundraft whenever they get a redesign in 2018 or 2019. You can get a very nice tundra for the price of a mid range gm or ford also.

Hope this isn't a repeat but just found this on the GM Techlink. I think this was done to mine last week.

Harsh Shifting on the 8L90 Automatic Transmission

December 8, 2016

There may be several harsh shifting conditions on some 2015-2016 Silverado, Sierra, Yukon and Escalade models equipped with the 5.3L engine (RPO L83) or 6.2L engine (RPO L86) and the 8L90 automatic transmission (RPOs M5U, M5X). The shift conditions may include:

• Harsh 1-2 upshift (except for the first 1-2 upshift of the day)

• Harsh 3-1 downshift when de-accelerating to a stop

• Harsh downshift under heavy throttle apply

• Active Fuel Management (AFM) V4 to V8 transition harshness (6.2L engine only)

• Coast-down downshifts (6.2L engine only)

There is new Engine Control Module (ECM) and/or Transmission Control Module (TCM) software that is available to improve these conditions. Use the Service Programming System (SPS) and follow the on-screen instructions to complete the programming. If both controller options are listed in SPS, select K20/K71 Transmission Control Module.

Do not install this calibration if the vehicle is not exhibiting these conditions. It is not intended to be installed on these vehicles for any other conditions.

TIP: Installation of the new TCM software will require that the Transmission Service Fast Learn (SFL) procedure be performed using GDS 2 or SPS through the TIS2Web application. The transmission may exhibit poor shift quality until the clutch values are learned. Performing the SFL will reset and relearn all the shift adapts.

After the programming of the TCM (Fig. 16) is complete, evaluate the shift quality of the transmission. Refer to Bulletin #16-NA-019 for more information about the transmission adaptive functions, how to learn the clutches and improve shift quality.

TIP: Due to the installation of the new TCM software, Bulletin #14-07-30-001 should not be used on 2015 model year vehicles. It will not allow for proper clutch learning.

F16 TCM

Fig. 16

Transmission Shift Adapts

The 8-Speed automatic transmission (Fig. 17) uses a line pressure and volume control system during upshifts to compensate for new transmission build variation as well as the normal wear of transmission components. The variation from new and normal wear of the apply components within the transmission over time can cause shift time (the time required to apply a clutch) to be longer or shorter than desired.

2015 Hydra-Matic 8L90 (M5U) Eight Speed RWD Automatic Transaxle

Fig. 17

In order to compensate for these changes, the TCM adjusts the pressure commands to the various pressure control (PC) solenoids to maintain the originally calibrated shift timing. Referred to as “adaptive learning,” this adjusting process ensures a consistent shift feel and increases transmission durability. Transmission adapts can be reset and relearned using the Transmission Service Fast Learn procedure that is completed in the service stall.

When the Service Fast Learn is complete, perform a test drive and note any soft or harsh shifts. Within GDS 2, a Transmission Service Fast Learn Data page is available to aid in performing adaptive learning by showing throttle percentage, engine speed, transmission fluid temperature, and gear command.

For additional information, refer to this TechLink article on reprogramming the 8L90 transmission or the TechLink article providing an overview of the new 8L90 transmission.

– Thanks to Matt Bunting and Dave Peacy

Poffdaddy · March 13, 2017

On the GM tis calibration update search website you can put in your vin number and it will show if there are any calibration updates. When I put my vin number in it said there was an updated transmission calibration for my 8 speed. There was actually 4 part numbers for different calibrations. If I took it in for an oil change wouldn't a dealership automatically apply all applicable updates to any vehicle that has any outstanding? It would be the same as your phone asking you to update to latest software.

Ron.s · March 13, 2017

On the GM tis calibration update search website you can put in your vin number and it will show if there are any calibration updates. When I put my vin number in it said there was an updated transmission calibration for my 8 speed. There was actually 4 part numbers for different calibrations. If I took it in for an oil change wouldn't a dealership automatically apply all applicable updates to any vehicle that has any outstanding? It would be the same as your phone asking you to update to latest software.

I think that recalls are the only thing automatically updated. Some TSB's may be applied to all units but others are there for customers that report a problem that the TSB addresses. The TSB should include instructions for the dealership.

MT Groove · March 19, 2017

My 2016 Denali 6.2L 8 speed transmission has been clunking since 650 miles on the odo. Been to the dealer 3 times. First time, they had it 2.5 weeks; flush fluids and did some reprogramming. Second time, 2 weeks, they replaced the valve body. Third time, 1 week, service manager says he looked up all the TSBs, keeps on saying this is normal operation on the 8spds. This is the most bullshit I have yet to experience with any new vehicle purchase.

Colossus · March 19, 2017

That bullshit is pretty much the new norm in the automotive industry. Expect to see more of it from all manufacturers. Ford, Crapota, Dodge, GM, Honda, Lexus, Nissan.. it doesn't matter. Go visit their forums and you'll see people just like you who get the "We've done all we can and according to our engineers it is working as designed."

I'd be pissed too.

Edited March 19, 2017 by Colossus

Ron.s · March 19, 2017

My 2016 Denali 6.2L 8 speed transmission has been clunking since 650 miles on the odo. Been to the dealer 3 times. First time, they had it 2.5 weeks; flush fluids and did some reprogramming. Second time, 2 weeks, they replaced the valve body. Third time, 1 week, service manager says he looked up all the TSBs, keeps on saying this is normal operation on the 8spds. This is the most bullshit I have yet to experience with any new vehicle purchase.

Re: My post of March 11 above. I got the same story you did and about 30 days ago the dealer said they couldn't duplicate any harsh shifting. They "might" follow up and try to drive it around a day until they could get a repeat of my complaint. I know that would never happen....expensive and GM would never OK it. Went to this site http://sandyblogs.com/techlink/ and found the Techlink Article quoted above. Took a copy of the Bullrtin back to the dealer and the Service Writer seemed to agree that it applied. 4 days later and no rough shifting and it's much smoother now...more like when it was new. I didn't get any documentation yet because they didn't get my GPS Antenna replaced and delivered my truck back to me. I left town the next day and have an appointment in 2 weeks to finish up. I haven't done a lot of city driving so I can't be 100% certain but so far no clunky shifts and upshifts are slower-holding longer more R's but still a smooth up shift and downshift.

MT Groove · March 27, 2017

That bullshit is pretty much the new norm in the automotive industry. Expect to see more of it from all manufacturers. Ford, Crapota, Dodge, GM, Honda, Lexus, Nissan.. it doesn't matter. Go visit their forums and you'll see people just like you who get the "We've done all we can and according to our engineers it is working as designed."

I'd be pissed too.

You are probably right. They all have their issues. However, the last new Toyota, BMW, Ford purchase I made has been a great experience. 650 miles into my GMC and I started regretting my decision.

Re: My post of March 11 above. I got the same story you did and about 30 days ago the dealer said they couldn't duplicate any harsh shifting. They "might" follow up and try to drive it around a day until they could get a repeat of my complaint. I know that would never happen....expensive and GM would never OK it. Went to this site http://sandyblogs.com/techlink/ and found the Techlink Article quoted above. Took a copy of the Bullrtin back to the dealer and the Service Writer seemed to agree that it applied. 4 days later and no rough shifting and it's much smoother now...more like when it was new. I didn't get any documentation yet because they didn't get my GPS Antenna replaced and delivered my truck back to me. I left town the next day and have an appointment in 2 weeks to finish up. I haven't done a lot of city driving so I can't be 100% certain but so far no clunky shifts and upshifts are slower-holding longer more R's but still a smooth up shift and downshift.

Any updates? Does your truck still drive OK?

Ron.s · March 27, 2017

Any updates? Does your truck still drive OK?

So far so good, no harsh shifts and a week of stop and go driving. They reset the "learn" function so that should be done by now. Upshifts may be a little crisper, not a bad thing. My slip yoke is sticking (infrequent and not bad) so back to the Driveline Shop for grease for the third time soon. Almost 21,000 so hoping it wears in soon and stops sticking. Common problem according to DL shop.

pm26 · March 29, 2017

The 8-Speed automatic transmission (Fig. 17) uses a line pressure and volume control system during upshifts to compensate for new transmission build variation as well as the normal wear of transmission components.

I doubt it can compensate for "build variation" caused by faulty components and /or shoddy assembly. And that's the core of the problem here.

nate18211 · April 7, 2017

Hey guys just want to share my transmission adventure with everyone. I have a 2016 Silverado LT with 12500 miles, 5.3 with 3.42 gears. I've always had a slight vibration at higher speeds. 65-80 mph but nothing extreme and clunky shifting. Dealer of course said it was normal. Occasionally would get a good clunk on downshifts under a load. My house is on a steep hill so usually when going up then slowing down at the top of the hill I would feel it. About 5000 miles ago it began clunking when in stop and go traffic on up and downshifts. Again dealer said it was normal. Lately it was clunking between 30-50 mph usually when merging into traffic, up shifting. Had all "computer" recalls done at the dealership.

This morning while on the highway in the third lane going around 50, it felt as if I hit a large pothole, but there was none and the engine just revved. It just popped out of gear. I pulled over and tried to go. It would shift fine from 1-3 gear then it revs and would not catch 4th. I pulled over again and tried it in manual mode. Same thing, would not engage 4-6th gear. I called the dealership they told me to turn it off and on, open and close the door to reset the transmission computer. Same thing would not go past 4th gear.

So its in the shop now. I'll let you guys know what the deal is. I'm very disappointed as this is my first Chevy and first pickup truck. I know I bought a truck but this thing lacks any finesse and new car feel. The vibration, transmission issues, and shitty idle make it feel like a POS. I know this is an unfair comparison and their quality has gone down in the last few years, but my wife and I have always leased Toyota SUV's. From day one to the vehicles return they never had an issues and felt new. My father has a Tacoma, again not a apples to apples comparison, and he has had other issues like rust. But his trucks motor and transmission have been bullet proof, I've pulled a 18 foot cuddy cabin with his truck for years and never a hiccup. The only issues came when he put "off-road" tires, then he complained about vibration but that was expected.

Edited April 7, 2017 by nate18211

11bDad · April 8, 2017

While 100 miles out of town my tranny did the same thing as nate18211 experienced. First trip to the dealer they replaced the TEHCM (TCM), which didn't help. Second trip they blamed it on 2 bad fuel injectors which GM instructed them to replace all 6 which did nothing. Third trip they said they couldn't replicate the problem. Took it to another dealer where they replaced the torque converter and pump. Issue solved. I had always felt uncomfortable with the high tranny temps I was seeing (I know it's designed to run 190* plus), so I added a 20K btu tranny cooler and modified the transmission Thermal Bypass Valve. Temps are now 30 degrees cooler, the wonky downshifting has been eliminated, and the 2-3 flair shifting only happens occasionally. Good luck getting it sorted out.

Edited April 8, 2017 by 11bDad

kiwihiwi · April 9, 2017

My truck's transmission Has issues too. On a 2015 Sierra 2015 slt, 45000 miles. One big clunk noise from underneath and now no more power. Engine light on, d-light blinks, manual doesn't lock in, but vehicle moves, backupcamera doesn't turn on in Reverse. Reader says transmission issue with power loss. for some reason these trucks don't seem to last anymore. Pretty disappointed. Last truck was a complete fail, had to sell it back this one goes to shit after 45000 miles.........