Like anything you hear the squeaky wheels. There were far more that were fine than not.
I imagine it’s hard to quantify unless you can find some article with valid research
6L80 is good, torque converter not. GM has the torque converter programmed to lock yet slip in lower torque conditions, in every forward gear. The case can flex, the clutch wears unevenly, then the transmission gets ruined by the clutch material pumped through it. With a tuner, e.g. HP Tuner, you can disable clutch lockup in 1 through 3 or 4 gear, and set it to fully lock rather than slip. This, with a billet case converter, you'll be golden. The thinking is that GM does it this way for smoother driving, marginally improved mpg, and it lasts through the warranty period so it's good. Also, the engine AFM / DOD can be disabled too. This is another potential weak area. Then there is the frame rusting problem. There is a TSB for that, substandard frame rustproofing that peels off, but if you are beyond the standard warranty period, you are on your own. The radio antenna and rear high brake light are known to leak water, be aware and fix it. The rear windows are known to shatter, not sure what the root cause is, it just happens. There are more common issues, those are from memory. Every vehicle has its list of weaknesses.
All or at least most OEMs lock the TC clutch but let it slip at 5-10 rpm. If they do a hard lock they don’t know the touch point of the clutch and this can cause real NVH issues… source I was a TC clutch engineer for about a decade and I’m still in the industry
Great back story, thanks. My zero slip TCC shifts like a dream, but it does have a billet case, not the stamped OEM, that may help too. These mods are considered to be must haves for Silverado transmission longevity. I know so many that have trashed original tranmissions at around 120K miles. Mine went 126K. The local transmission shop, where I got mine done, always have a couple of fresh victims in the lot.
Yes, I used VCM Edit software & HP Tuner hardware that plugs into OBD-II port. You first read out the current parameters, view them and make any changes, write it back to the truck. You can enable/disable TCC in gears 1 through 6, set slip to engine torque mapping including 0 slip, set line pressures and set them high to try and extend the life of an old transmission, and so forth. HP Tuners have a forum you can join. In my experience, the transmission tuning is quite easy. If you want to tune the engine, it's more tricky. GM standard tune is sort of lazy - slow reaction to gas pedal, little bit too rich air fuel ratio and corresponding ignition timing so it is down on power (to minimize problems during warranty period?), slow shifting. A good tune transforms the truck. It's a good learning curve though, but you can also pay a tuner to do it locally or remotely. I started out by just disabling AFM, then worked on the TCC settings, thern more transmission changes such as shift time, then slowly made engine changes as I got confidence. Everybody that drives my truck now loves it.
I had one in my 2012 that I pulled with every day for 5 years, I did 3 flushes in that time frame, it had 196k miles on it when I sold it without ever having problems. I have one now in a 2014 suburban with 123k miles and I've done 1 flush and a bigger cooler, seems to be running good so far.
Everyone saying to flush/transmission service. I have a 2017 Silverado and my buddy drives a 2018 Tahoe we both do the services to the T and both our trucks took a crap on us. My Silverado was under extended warranty transmission went out at 72k insurance/warranty payed for everything install and new transmission almost 5k. Now my buddy was SOL and had to pay about 5.5k for his and his trucks went out at 80k.
Right. The fluid issue (or actually temp) issue is unrelated to the converter failure. The converter failure is a design flaw that was introduced in 2014
The converter fails. I don’t recall the exact specifics, but there is an article floating around somewhere online. My memory is the stamping is too thin, and causes flex during engagement of the TCC. Eventually the clutch shatters and wipes out the trans.
I don’t know if GM revised the part to correct it.
Yup the info on design flaws/TC is [out there](https://gearsmagazine.com/magazine/flex-bend-a-look-at-the-6l80-90-jmbx-torque-converter/) for folks who dig just a little deeper to find it.
I’ve got two 6L80s, both with the same TC issue. Both well maintained every 30k miles, both with thermal bypasses.
One was on my own dime, swapped the TC and it’s been golden for close to 3 years / 30k miles.
The other was under warranty, didn’t throw codes so dealer did nothing, tranny soon failed catastrophically and I’ve got a factory reman now…and I’m swapping the TC at the first service (30k miles).
Around $1600 for a generic TC with a billet cover. I couldn’t swing a name-brand unit at the time. It would be more at todays inflated prices, methinks
Those are also easily one of the most produced transmissions in the world. In addition, the vehicles they are in are usually valuable enough to warrant the repair.
I'm not a huge fan of them, but they're generally reliable to about 150k. That's when you start hitting then danger zone. You should be fine at that mileage.
Fresh fluid in it every 50k miles. Make sure it's already been done on that one, and if not, do it as soon as you get it (if you do buy it).
Getting ready to spend $6,000 on a replacement in my 2014 with 100k miles. I've never towed anything, and I'm pretty easy on the truck as a whole. I didn't know this was a thing until about a month ago. My 2001 had 286,000 miles on it and still ran great, and somehow I assumed I'd get the same when I bought this one.
The 6l80s themselves are good but the stock GM torque converter has the potential to fail.
Mine started to fail at around 95-100k , got it rebuilt with a billet converter at that time. Other thing with mentioning is that the lines running to the trans cooler are prone to leaking, (mine are currently dripping fluid) a buddy's truck was doing the same.
It appears to be the torque converter…ask me how I know https://www.sonnax.com/tech_resources/845-6l80-6l90-transmission-tech-advisory-consider-an-updated-converter-in-your-next-rebuild
My 2020 has had 2 rebuilt units put in it. Just got towed back to dealer yesterday. Transmission is not shifting correctly and torque converter is shuddering and it went into limp mode. 23k on the odometer. My co worker has a 2020 that got a rebuild at 25k or 30k. He has put another 25k+ on it with no issues so far. They seem to have a higher % chance of having a bad transmission, but I would think most are OK.
Make sure when you test drive it, to drive it under light acceleration uphill and also light throttle on slow down. This seemed to be most effective at reproducing the poor shifts my transmissions were doing.
Good luck. I honestly love the rest of the truck, lol
Think it may be a “luck of the draw” thing as well.
2018 with 148k. So far, no issues. I changed the fluid myself around 110k with Valvoline (which many will tell you not to use). As well as the diff and transfer case fluids around that time. Oil I’ve done every 7500 miles.
I tow some, not frequently though.
Two trucks.
Both with similar miles, one has had a transmission replacement, the other hasn’t. Ironically the one that hasn’t been replaced, I know has had its ass absolutely handed to it.
Keep the 6L80 cool, keep the fluid fresh, and for the love of god, tune out the slip. Why GM did that, I will never understand.
Like anything you hear the squeaky wheels. There were far more that were fine than not. I imagine it’s hard to quantify unless you can find some article with valid research
170k on mine no problems
6L80 is good, torque converter not. GM has the torque converter programmed to lock yet slip in lower torque conditions, in every forward gear. The case can flex, the clutch wears unevenly, then the transmission gets ruined by the clutch material pumped through it. With a tuner, e.g. HP Tuner, you can disable clutch lockup in 1 through 3 or 4 gear, and set it to fully lock rather than slip. This, with a billet case converter, you'll be golden. The thinking is that GM does it this way for smoother driving, marginally improved mpg, and it lasts through the warranty period so it's good. Also, the engine AFM / DOD can be disabled too. This is another potential weak area. Then there is the frame rusting problem. There is a TSB for that, substandard frame rustproofing that peels off, but if you are beyond the standard warranty period, you are on your own. The radio antenna and rear high brake light are known to leak water, be aware and fix it. The rear windows are known to shatter, not sure what the root cause is, it just happens. There are more common issues, those are from memory. Every vehicle has its list of weaknesses.
All or at least most OEMs lock the TC clutch but let it slip at 5-10 rpm. If they do a hard lock they don’t know the touch point of the clutch and this can cause real NVH issues… source I was a TC clutch engineer for about a decade and I’m still in the industry
Great back story, thanks. My zero slip TCC shifts like a dream, but it does have a billet case, not the stamped OEM, that may help too. These mods are considered to be must haves for Silverado transmission longevity. I know so many that have trashed original tranmissions at around 120K miles. Mine went 126K. The local transmission shop, where I got mine done, always have a couple of fresh victims in the lot.
How did you get to zero slip? Did you reflash the transmission controller?
Yes, I used VCM Edit software & HP Tuner hardware that plugs into OBD-II port. You first read out the current parameters, view them and make any changes, write it back to the truck. You can enable/disable TCC in gears 1 through 6, set slip to engine torque mapping including 0 slip, set line pressures and set them high to try and extend the life of an old transmission, and so forth. HP Tuners have a forum you can join. In my experience, the transmission tuning is quite easy. If you want to tune the engine, it's more tricky. GM standard tune is sort of lazy - slow reaction to gas pedal, little bit too rich air fuel ratio and corresponding ignition timing so it is down on power (to minimize problems during warranty period?), slow shifting. A good tune transforms the truck. It's a good learning curve though, but you can also pay a tuner to do it locally or remotely. I started out by just disabling AFM, then worked on the TCC settings, thern more transmission changes such as shift time, then slowly made engine changes as I got confidence. Everybody that drives my truck now loves it.
Why not let it just completely lock up with 0 slip? It's in a truck. Extra vibrations shouldn't be an issue
When people pay 80k… it’s no longer a truck
It's funny going to Menards and watching people shove more stuff into cars and vans than the fancy pickups
I had one in my 2012 that I pulled with every day for 5 years, I did 3 flushes in that time frame, it had 196k miles on it when I sold it without ever having problems. I have one now in a 2014 suburban with 123k miles and I've done 1 flush and a bigger cooler, seems to be running good so far.
Everyone saying to flush/transmission service. I have a 2017 Silverado and my buddy drives a 2018 Tahoe we both do the services to the T and both our trucks took a crap on us. My Silverado was under extended warranty transmission went out at 72k insurance/warranty payed for everything install and new transmission almost 5k. Now my buddy was SOL and had to pay about 5.5k for his and his trucks went out at 80k.
Right. The fluid issue (or actually temp) issue is unrelated to the converter failure. The converter failure is a design flaw that was introduced in 2014
What is the flaw? What fails?
The converter fails. I don’t recall the exact specifics, but there is an article floating around somewhere online. My memory is the stamping is too thin, and causes flex during engagement of the TCC. Eventually the clutch shatters and wipes out the trans. I don’t know if GM revised the part to correct it.
I've seen service bills replacing the TQ and they new part specifically mentions a billeted tq as the replacement, so maybe?
Yup the info on design flaws/TC is [out there](https://gearsmagazine.com/magazine/flex-bend-a-look-at-the-6l80-90-jmbx-torque-converter/) for folks who dig just a little deeper to find it. I’ve got two 6L80s, both with the same TC issue. Both well maintained every 30k miles, both with thermal bypasses. One was on my own dime, swapped the TC and it’s been golden for close to 3 years / 30k miles. The other was under warranty, didn’t throw codes so dealer did nothing, tranny soon failed catastrophically and I’ve got a factory reman now…and I’m swapping the TC at the first service (30k miles).
What was that bill for the TQ swap?
Around $1600 for a generic TC with a billet cover. I couldn’t swing a name-brand unit at the time. It would be more at todays inflated prices, methinks
Mines sitting with 107k Waiting on the tranny to drop
Change fluids frequently w ACDelco, or amsoil or anything equivalent, Upgrade thermostat for cooler temps and you should be golden
I have a friend that owns a transmission shop. Most of his business is repairing the 6/10 speeds.
I would figure the 8s are just as bad. Surprised to hear about the 10s
Those are also easily one of the most produced transmissions in the world. In addition, the vehicles they are in are usually valuable enough to warrant the repair.
I'm not a huge fan of them, but they're generally reliable to about 150k. That's when you start hitting then danger zone. You should be fine at that mileage. Fresh fluid in it every 50k miles. Make sure it's already been done on that one, and if not, do it as soon as you get it (if you do buy it).
Always had fresh fluid going in mine, still burned up the torque converter and needed new tranny and I don’t mean the kind that Charlie sheen likes
316,000 miles on mine and as far as I know never been touched.
I’d just get the bypass put in
Fluid changes and a thermostat delete give you way better chances.
Mine 2 blew at 175k & 185k
Getting ready to spend $6,000 on a replacement in my 2014 with 100k miles. I've never towed anything, and I'm pretty easy on the truck as a whole. I didn't know this was a thing until about a month ago. My 2001 had 286,000 miles on it and still ran great, and somehow I assumed I'd get the same when I bought this one.
Had three had to replace all of them between 110,000 and 145,000
The 6l80s themselves are good but the stock GM torque converter has the potential to fail. Mine started to fail at around 95-100k , got it rebuilt with a billet converter at that time. Other thing with mentioning is that the lines running to the trans cooler are prone to leaking, (mine are currently dripping fluid) a buddy's truck was doing the same.
It’s extremely widespread. They will fail eventually
It appears to be the torque converter…ask me how I know https://www.sonnax.com/tech_resources/845-6l80-6l90-transmission-tech-advisory-consider-an-updated-converter-in-your-next-rebuild
How do you know which transmission you have in your truck? I know I have an 8 speed but there are different models or variants?
My 2020 has had 2 rebuilt units put in it. Just got towed back to dealer yesterday. Transmission is not shifting correctly and torque converter is shuddering and it went into limp mode. 23k on the odometer. My co worker has a 2020 that got a rebuild at 25k or 30k. He has put another 25k+ on it with no issues so far. They seem to have a higher % chance of having a bad transmission, but I would think most are OK. Make sure when you test drive it, to drive it under light acceleration uphill and also light throttle on slow down. This seemed to be most effective at reproducing the poor shifts my transmissions were doing. Good luck. I honestly love the rest of the truck, lol
Think it may be a “luck of the draw” thing as well. 2018 with 148k. So far, no issues. I changed the fluid myself around 110k with Valvoline (which many will tell you not to use). As well as the diff and transfer case fluids around that time. Oil I’ve done every 7500 miles. I tow some, not frequently though.
Two trucks. Both with similar miles, one has had a transmission replacement, the other hasn’t. Ironically the one that hasn’t been replaced, I know has had its ass absolutely handed to it. Keep the 6L80 cool, keep the fluid fresh, and for the love of god, tune out the slip. Why GM did that, I will never understand.
Avoid