GM 6L80 Transmission Information Thread

[shrutefarms12]

@NickTransmissions

Sorry in advance if this is not the place to post this. I tried sending a PM but system would not allow me to send it. I have a 2018 tahoe that has had its 6l80e replaced by my local chevy dealer @90k miles. They installed the updated thermostat on the transmission that supposedly keeps trans fluid cooler. Ever since the new transmission got installed, anytime I am towing anything moderately heavy like my boat (6k pounds) the transmission temps slowly build until it hits 280 degrees and goes into limp mode. I have brought it back to dealer many times and they replaced the TEHCM module but that still has not solved the issue. Any ideas what could be going on? Dealer basically said to blow it up again for them to do anything else. Seems they don't believe me even though I have many pictures. I am approaching the end of the warranty period and want to get this figured out before it expires. Any insight would be greatly appreciated.

Thanks! -Nick

 

[donjetman]

you need to install an aftermarket trans cooler setup like many folks here have done.

 

[NickTransmissions]

@NickTransmissions

Sorry in advance if this is not the place to post this. I tried sending a PM but system would not allow me to send it. I have a 2018 tahoe that has had its 6l80e replaced by my local chevy dealer @90k miles. They installed the updated thermostat on the transmission that supposedly keeps trans fluid cooler. Ever since the new transmission got installed, anytime I am towing anything moderately heavy like my boat (6k pounds) the transmission temps slowly build until it hits 280 degrees and goes into limp mode. I have brought it back to dealer many times and they replaced the TEHCM module but that still has not solved the issue. Any ideas what could be going on? Dealer basically said to blow it up again for them to do anything else. Seems they don't believe me even though I have many pictures. I am approaching the end of the warranty period and want to get this figured out before it expires. Any insight would be greatly appreciated.

Thanks! -Nick

I've shut off all inbound *** - there's absolutely no reason for me to provide tech support via PM as it's duplicative, redundant and defeats the purpose of having an open forum (not to mention a total waste of my time). So you posted this in the right place.

You must flip the pill or install a thermal bypass valve delete kit and add a large aftermarket transmission cooler to your set up. The updated T-stat still restricts fluid flow based on temp and ultimately results in the transmission running hotter than it should. Those stupid TBVs are pointless unless you live in Canada or Alaska.

 

[Geotrash]

@NickTransmissions

Sorry in advance if this is not the place to post this. I tried sending a PM but system would not allow me to send it. I have a 2018 tahoe that has had its 6l80e replaced by my local chevy dealer @90k miles. They installed the updated thermostat on the transmission that supposedly keeps trans fluid cooler. Ever since the new transmission got installed, anytime I am towing anything moderately heavy like my boat (6k pounds) the transmission temps slowly build until it hits 280 degrees and goes into limp mode. I have brought it back to dealer many times and they replaced the TEHCM module but that still has not solved the issue. Any ideas what could be going on? Dealer basically said to blow it up again for them to do anything else. Seems they don't believe me even though I have many pictures. I am approaching the end of the warranty period and want to get this figured out before it expires. Any insight would be greatly appreciated.

Thanks! -Nick

One of the stupid shop tricks I've read here several times is that when they replace the transmission after a failure, many of them simply bypass the radiator's end tank oil-to-water heat exchanger rather than replace the radiator. They do this ostensibly to protect the new transmission from any debris still trapped in the exchanger. But as I've learned first-hand, doing this will result in seriously elevated fluid temperatures when towing. My guess is that this is what they did in your case.

Your truck should have BOTH the radiator end tank exchanger AND an external transmission cooler plumbed IN SERIES with each other.

Trace the cooler lines from the transmission to the coolers and back and let us know what you find. If I'm right, then the solution is to replace the radiator with a Denso (OEM manufacturer). If the external cooler is still in the circuit then plumb it in DOWNSTREAM from the radiator's heat exchanger. If the external cooler is NOT plumbed in currently, then replace it with a new one and plumb it in downstream from the radiator. I say this last part because if they bypassed it then it's likely still filled with debris.

Net/Net: you want BOTH a clean radiator end tank heat exchanger AND a clean external fluid cooler plumbed in series. The heat exchanger takes a big cut of heat out of the fluid before it hits the external cooler. Trust me on this. I have done the experiments myself.

 

[alpha_omega]

One additional caveat to the previous recommendations from @Geotrash @NickTransmissions & @donjetman would be to add a larger (deep) transmission pan. I’ve been very happy with the build quality of B&M, and by installing it, I haven’t had to go the extra step of adding larger fan motors. Not yet anyways, and I tow very heavy trailers in high fairly high summer temps.
Best of luck and keep us posted.

 

[rbrickey37660]

@NickTransmissions
i'm a new member here and have been searching forms looking for some help or education.....so here's what happened.
My 2012 tahoe transmission started acting up..Honestly it was serviced like it should have been anyway it's got around 225k on it and pretty much overheated and killed it.
So had it towed to a transmission shop..I'm located in Tennessee...The owner told me they would rebuild it and retune motor/transmission..3yr/50k mile warranty for $5100....so they call said it's ready...I picked it up and start home roughly 45 mile trip...on the interstate i'm watching the transmission temp and on the first kinda long uphill maybe 30 miles into my trip home temp starts rising at gets to around 225 and by the time i was able to get off the interstate it was around 260 or so...had it towed back to the shop....they replaced the transmission cooler radiator the small one and i'm assuming rebuilt it again....so they call...I pick it up...almost the same thing again but this time i was able to get off the interstate when the temp got to around 230 but it got probably close to 250 before i could stop......so they tetxed me today and said they are ordering the Techm and they put a dorman in it and it didnt get hot except was flaring up in 3rd gear so they are ordering an AC delco to try but that it had done fine on the interstate. i was just wanting your input because you are an expert and like i said i not really sure how transmissions work but it just seems like to me that the fluid isnt circulating to stay cool....Thanks for any input you may have.

Robbie

 

[NickTransmissions]

@NickTransmissions
i'm a new member here and have been searching forms looking for some help or education.....so here's what happened.
My 2012 tahoe transmission started acting up..Honestly it was serviced like it should have been anyway it's got around 225k on it and pretty much overheated and killed it.
So had it towed to a transmission shop..I'm located in Tennessee...The owner told me they would rebuild it and retune motor/transmission..3yr/50k mile warranty for $5100....so they call said it's ready...I picked it up and start home roughly 45 mile trip...on the interstate i'm watching the transmission temp and on the first kinda long uphill maybe 30 miles into my trip home temp starts rising at gets to around 225 and by the time i was able to get off the interstate it was around 260 or so...had it towed back to the shop....they replaced the transmission cooler radiator the small one and i'm assuming rebuilt it again....so they call...I pick it up...almost the same thing again but this time i was able to get off the interstate when the temp got to around 230 but it got probably close to 250 before i could stop......so they tetxed me today and said they are ordering the Techm and they put a dorman in it and it didnt get hot except was flaring up in 3rd gear so they are ordering an AC delco to try but that it had done fine on the interstate. i was just wanting your input because you are an expert and like i said i not really sure how transmissions work but it just seems like to me that the fluid isnt circulating to stay cool....Thanks for any input you may have.

Robbie

This is speculation but seems as though there's a partial restriction in your system. The shop should have flushed the lines and cooler(s) prior to installation of the rebuilt transmission. Not sure why they are using Dorman but nothing that company makes is any good. They should have installed a GM OEM brand new TEHCM, IMS and speed sensor/harness assembly in addition to a whole host of other things. Then they would have had to program the TEHCM to your VIN as GM TEHCMs do not come pre-programmed.

Beyond that, it's up to them to get it right - nothing else for me to add.

 

[rbrickey37660]

This is speculation but seems as though there's a partial restriction in your system. The shop should have flushed the lines and cooler(s) prior to installation of the rebuilt transmission. Not sure why they are using Dorman but nothing that company makes is any good. They should have installed a GM OEM brand new TEHCM, IMS and speed sensor/harness assembly in addition to a whole host of other things. Then they would have had to program the TEHCM to your VIN as GM TEHCMs do not come pre-programmed.

Beyond that, it's up to them to get it right - nothing else for me to add.

Thanks for the response....they have an GM oem TEHCM on order that they are going to changed out....I'm not sure what all was replaced but it was supposed to be a complete rebuild....so like you said it's on them to get it right. Thanks again!

 

[alpha_omega]

@NickTransmissions can you explain the difference in a 4-5-6 Clutch Apply Piston Kit having an Apply Plate versus one with an Apply Ring?

When would one be chosen over the other?
I understand the difference, one eliminates the wave plate and has “harder” shift patterns, but why would you want one over the other and is there actual benefit in a plate versus a ring?


Sonnax High Capacity 4-5-6 Clutch Apply Piston Kit part no. 104960-01K

Heavy Duty 4-5-6 Clutch Apply Piston Kit - 104960-01K

Improved clutch apply for increased durability. Apply ring and thicker backing plate improve clutch apply and reduce buildup. Fits 6L80, 6L90. Part# 104960-01K

www.sonnax.com

the other 104960-10K

High Capacity 4-5-6 Clutch Apply Piston Kit - 104960-10K

17% More clutch capacity. Patent-pending, toothed apply plate eliminates OE waved plate to allow one additional friction. Fits 6L80, 6L90. Part # 104960-10K

www.sonnax.com

 

[NickTransmissions]

@NickTransmissions can you explain the difference in a 4-5-6 Clutch Apply Piston Kit having an Apply Plate versus one with an Apply Ring?

When would one be chosen over the other?
I understand the difference, one eliminates the wave plate and has “harder” shift patterns, but why would you want one over the other and is there actual benefit in a plate versus a ring?


Sonnax High Capacity 4-5-6 Clutch Apply Piston Kit part no. 104960-01K

Heavy Duty 4-5-6 Clutch Apply Piston Kit - 104960-01K

Improved clutch apply for increased durability. Apply ring and thicker backing plate improve clutch apply and reduce buildup. Fits 6L80, 6L90. Part# 104960-01K

www.sonnax.com

the other 104960-10K

High Capacity 4-5-6 Clutch Apply Piston Kit - 104960-10K

17% More clutch capacity. Patent-pending, toothed apply plate eliminates OE waved plate to allow one additional friction. Fits 6L80, 6L90. Part # 104960-10K

www.sonnax.com

Hi-Cap = one additional clutch and steel (see the description you linked)....The other one is stock dimensions for stock clutch pack configuration but beefier. Air bleed typically gets turned off in the 4-5-6 shift table when running the Sonnax hi-cap kit as it eliminates the cushion plate while the other one keeps it.

 

[rbrickey37660]

This is speculation but seems as though there's a partial restriction in your system. The shop should have flushed the lines and cooler(s) prior to installation of the rebuilt transmission. Not sure why they are using Dorman but nothing that company makes is any good. They should have installed a GM OEM brand new TEHCM, IMS and speed sensor/harness assembly in addition to a whole host of other things. Then they would have had to program the TEHCM to your VIN as GM TEHCMs do not come pre-programmed.

Beyond that, it's up to them to get it right - nothing else for me to add.

Update.....the shop can't figure out what is going on...they have ordered a new transmission from dealer. They have built and put the 3 different transmissions in it and all 3 do the same thing...not holding lockup. They are saying that is why they are overheating and burning up.

 

[NickTransmissions]

Update.....the shop can't figure out what is going on...they have ordered a new transmission from dealer. They have built and put the 3 different transmissions in it and all 3 do the same thing...not holding lockup. They are saying that is why they are overheating and burning up.

My guess is the new one will also burn to the ground for the same reason. Three diff transmissions failing like that, same problem points to an issue with that vehicle or shop. Gotta find out which of those two is the source of the problem.

 

[alpha_omega]

Hi-Cap = one additional clutch and steel (see the description you linked)....The other one is stock dimensions for stock clutch pack configuration but beefier. Air bleed typically gets turned off in the 4-5-6 shift table when running the Sonnax hi-cap kit as it eliminates the cushion plate while the other one keeps it.

So you only choose the Hi-Cap if you were not using the stock clutch pack, correct?

 

[NickTransmissions]

So you only choose the Hi-Cap if you were not using the stock clutch pack, correct?

You just buy one more 3-5-R friction disc and flat steel and eliminate the waved cushion plate at the bottom of the pack.

 

[rbrickey37660]

My guess is the new one will also burn to the ground for the same reason. Three diff transmissions failing like that, same problem points to an issue with that vehicle or shop. Gotta find out which of those two is the source of the problem.

Another update.....the shop installed the new one and same result...so they are ordering an engine computer and transmission computer....they are saying it's not an mechanical fault so it has to be in the computer....i wasn't experiencing any computer issues that I was aware...when it broke down original the transmission temperature was around 200 degree on the DIC and it seemed like it was just starting to bind up and clunking when shifting. Thoughts???

 

[Geotrash]

Another update.....the shop installed the new one and same result...so they are ordering an engine computer and transmission computer....they are saying it's not an mechanical fault so it has to be in the computer....i wasn't experiencing any computer issues that I was aware...when it broke down original the transmission temperature was around 200 degree on the DIC and it seemed like it was just starting to bind up and clunking when shifting. Thoughts???

Hmmmm....I'm wondering how they routed the coolers. There is a transmission oil-to-water cooler in the pax side end tank of the radiator AND an additional oil-to-air cooler mounted in front of the radiator. They BOTH need to be plumbed in series with each other, with the radiator end tank plumbed into the circuit BEFORE the cooler in front of the radiator. Some shops delete the radiator's cooler from the circuit to avoid having debris from the initial failure take out the new transmission, and take a shortcut by just replacing the external cooler.

The radiator's cooler takes a HUGE chunk of heat out of the fluid because oil-to-water coolers are so much more efficient. Trust me on this - I have run the experiments myself on my 2012 with different cooler configurations to get my towing temps under control.

 

[rbrickey37660]

Finally got my Tahoe back yesterday....the shop actually delivered it to my house. I took it on a pretty long drive when I got home and the transmission temp never got over 170 which I thought was good considering the temp was in the mid 90s. The shop told me they ended up putting 3 transmissions in it and switched out the ECM along with the TCM. They also did a tune on the transmission. I don't have a full parts breakdown of what was replaced, I'm just glad it fixed and running good again. I do have a 3yr/50K warranty as well.

 

[alpha_omega]

Finally got my Tahoe back yesterday....the shop actually delivered it to my house. I took it on a pretty long drive when I got home and the transmission temp never got over 170 which I thought was good considering the temp was in the mid 90s. The shop told me they ended up putting 3 transmissions in it and switched out the ECM along with the TCM. They also did a tune on the transmission. I don't have a full parts breakdown of what was replaced, I'm just glad it fixed and running good again. I do have a 3yr/50K warranty as well.

Do you know what tune they did? You might want to ensure that’s adjusted so it doesn’t burn through the clutches with its OEM tune. I realize it’s no longer OEM, but if you haven’t already, you’ll want it adjusted based off your driving style and use. BB Tune or HP is your best route.

 

[CTX-SLPR]

Howdy folks,

Just swapped out my 6L80 with a rebuilt unit after loosing confidence in the hard parts of the existing reman. I also added a Tru-Cool 40K cooler and now my trans temps are holding around 140-150 in 100 weather from around 45min driving around town which was enough before to cause issues. Any downside to having it run at this temp when just cruising and carrying people or should I mask off part of the cooler to get the temps up into the 160-175 range? I am a lot more confident in the ability to tow with this cooler and billet TC now.

Thanks

 

[NickTransmissions]

Howdy folks,

Just swapped out my 6L80 with a rebuilt unit after loosing confidence in the hard parts of the existing reman. I also added a Tru-Cool 40K cooler and now my trans temps are holding around 140-150 in 100 weather from around 45min driving around town which was enough before to cause issues. Any downside to having it run at this temp when just cruising and carrying people or should I mask off part of the cooler to get the temps up into the 160-175 range? I am a lot more confident in the ability to tow with this cooler and billet TC now.

Thanks

140-150 is perfectly fine.