6l80 flares, thunks cold upshifts

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

TomH91

TYF Newbie
Joined
Feb 21, 2022
Posts
19
Reaction score
15
I’ve read thru the 6l80 threads but haven’t seen anything exactly like what I’m seeing with my 2009 Yukon Denali XL. The truck has just under 164k miles.

1. When cold and under light throttle or if I have to lift throttle slightly just before a 1-2 or 2-3 up shift, the transmission will shift with an audible clank. It doesn’t happen again after the first run through the gears. It doesn’t clunk on downshifts at all. Is this fixable, and does it need to be addressed?

2. I often get a flare on the 2-3 upshift. It used to be only when cold but can now happen any time under light throttle and can occur on the 3-4 sometimes. It doesn’t slip at any time and doesn’t flare under moderate or heavy throttle. The dealership says 2-3 flare is normal. They did a fluid/filter change and reset the shift adapts. It was better for a few days but went back to doing it. Maybe this is just regular old torque management weirdness.

I had a GM dealership check the trans and they said the fluid was dirty. This was a used truck and I checked the trans fluid myself a couple of times in the months before I took it in and the fluid was actually okay - not too dark or stinky and no burned smell. There is a powertrain warranty for the rest of 2023. I played along and did the fluid so I could show I had done maintenance to it for the sake of any future warranty claim. We have had it for 16 months and I plan to keep it another year at least and would like to be proactive if the trans is in the early stages of needing to be redone.
 

donjetman

Full Access Member
Joined
Oct 22, 2018
Posts
1,343
Reaction score
2,298
2. I often get a flare on the 2-3 upshift. It used to be only when cold but can now happen any time under light throttle and can occur on the 3-4 sometimes. It doesn’t slip at any time and doesn’t flare under moderate or heavy throttle. The dealership says 2-3 flare is normal. They did a fluid/filter change and reset the shift adapts. It was better for a few days but went back to doing it. Maybe this is just regular old torque management weirdness.
Us too

Our 07 6L80 does the 2-3 upshift flare but only when below normal operating temp and only above 3000 rpm. Anybody know what the DIY fix is (or not)? Should I be worried? I don't tow and I drive conservatively.

Otherwise no issues. Has always done this since we bought it 4 1/2 yrs ago w/130k miles. It now has 187k miles. I replaced the torque converter shortly after we bought it. I have changed the Dexron6 and filter a couple of times.
 

swathdiver

Full Access Member
Joined
May 18, 2017
Posts
19,100
Reaction score
25,022
Location
Treasure Coast, Florida
Joined
Mar 9, 2023
Posts
802
Reaction score
1,860
Location
The transmission bench
I’ve read thru the 6l80 threads but haven’t seen anything exactly like what I’m seeing with my 2009 Yukon Denali XL. The truck has just under 164k miles.

1. When cold and under light throttle or if I have to lift throttle slightly just before a 1-2 or 2-3 up shift, the transmission will shift with an audible clank. It doesn’t happen again after the first run through the gears. It doesn’t clunk on downshifts at all. Is this fixable, and does it need to be addressed?

2. I often get a flare on the 2-3 upshift. It used to be only when cold but can now happen any time under light throttle and can occur on the 3-4 sometimes. It doesn’t slip at any time and doesn’t flare under moderate or heavy throttle. The dealership says 2-3 flare is normal. They did a fluid/filter change and reset the shift adapts. It was better for a few days but went back to doing it. Maybe this is just regular old torque management weirdness.

I had a GM dealership check the trans and they said the fluid was dirty. This was a used truck and I checked the trans fluid myself a couple of times in the months before I took it in and the fluid was actually okay - not too dark or stinky and no burned smell. There is a powertrain warranty for the rest of 2023. I played along and did the fluid so I could show I had done maintenance to it for the sake of any future warranty claim. We have had it for 16 months and I plan to keep it another year at least and would like to be proactive if the trans is in the early stages of needing to be redone.
Common problem in the 6L family of transmissions...Flaring in any transmission is not normal, especially in a clutch-to-clutch transmission such as the 6Ls.

The most common reasons this happens are:
> 3-5-R regulator valve sticking in the bore (upper valve body)
> 3-5-R drum welds leaking at the base (under the 3-5-R apply piston)
> Inadequate seal between pump stator and 3-5-R drum (2006-E2009)
> in mid-2009, GM redesigned the stator to accept support o-rings underneath the three sealing rings and machined in cut-outs in the stator to 'lock' the sealing rings in place so this may or may not apply to your vehicle

Your 'clanks' / 'clunks' are likely the result of a worn compensator feed regulator valve (lower valve body)

Us too

Our 07 6L80 does the 2-3 upshift flare but only when below normal operating temp and only above 3000 rpm. Anybody know what the DIY fix is (or not)? Should I be worried? I don't tow and I drive conservatively.

Otherwise no issues. Has always done this since we bought it 4 1/2 yrs ago w/130k miles. It now has 187k miles. I replaced the torque converter shortly after we bought it. I have changed the Dexron6 and filter a couple of times.
See above.

if memory serves these problems can be alleviated by rebuilding the pressure switches in the TECHM on your kitchen table.


But, let's double check with our resident transmission expert, Nick. What say you @NickTransmissions ?
You can't actually rebuild the switches, just service them in place. These can be a source of drivability symptoms if enough debris gets into the pressure switch cover 'plate' but this usually happens when the torque converter some other major hard part fails. Drivability symptoms associated w/pressure switch failure include harsh to violent up/down shifts or momentary neutral conditions due to one or more switches experiencing intermittent failure (pressure switch circuit stuck open when it shouldn't).

If any one of those switches is bad, the TEHCM needs to be thrown in the trash.

Too bad GM decided to put all the electronic/electric solenoids and pressure switches into one assembly that costs a billion dollars to replace vs kept physically separate parts that can be replaced for $40.00 or less.

All - please see my 6L80 thread for more information.
 
OP
OP
T

TomH91

TYF Newbie
Joined
Feb 21, 2022
Posts
19
Reaction score
15
Thank you, Nick. I’ll plan to get it to a reputable trans shop before long and will revisit your thread for additional info.
 

donjetman

Full Access Member
Joined
Oct 22, 2018
Posts
1,343
Reaction score
2,298
I'd service the pressure switches if it would help? Otherwise I'll just lift on the gas pedal a little on the rare occasions I take over 3k rpm when its not warmed up. Thanks
 
Joined
Mar 9, 2023
Posts
802
Reaction score
1,860
Location
The transmission bench
I'd service the pressure switches if it would help? Otherwise I'll just lift on the gas pedal a little on the rare occasions I take over 3k rpm when its not warmed up. Thanks
You could but not sure it would make any difference. Since you have a 2007, your unit doesn't have many of the updates that went into these transmissions starting around mid-year 2009 where many of the failures that plagued those first three or so years worth of vehicles were addressed w/updated parts. So your flares are equally likely to have their underlying causes in the valve body or the case. Ultimately, the fix is to rebuild the transmission with updated parts including a Sonnax 1-2-3-4 piston, weld-reinforced 3-5-R drum and late model stator/pump cover assembly with the improved sealing ring design as those are the prime suspects inside the transmission case when drivability symptoms like slipping, flare shifts and harsh shifts begin to appear.
 
Last edited:

swathdiver

Full Access Member
Joined
May 18, 2017
Posts
19,100
Reaction score
25,022
Location
Treasure Coast, Florida
You can't actually rebuild the switches, just service them in place.

If any one of those switches is bad, the TEHCM needs to be thrown in the trash.
So Nick, you are saying that it's not worth using this kit to restore them to working order?

1686263908927.png
 
Joined
Mar 9, 2023
Posts
802
Reaction score
1,860
Location
The transmission bench
So Nick, you are saying that it's not worth using this kit to restore them to working order?

View attachment 401414
It can definitely be worth it under certain circumstances. I use that kit on all rebuilds where we're not replacing the TEHCM but as far as repairing a fault in one of the solenoids or malfunctioning pressure switch, that kit wont make a diff as it's not designed to fix those sort of faults. It's primarily designed to restore the positive seal for the pressure switches via replacement seals. Leaking seals can also cause flairs, etc but they'd have to very degraded (see it when the trans overheats, turns those seals hard thus they leak).

But if the TEHCM doesn't pass the resistance or voltage tests, the above kit won't restore it.

For those that haven't seen the pressure switch parts off the TEHCM, here's a pic:
IMG_7443.jpeg
 

swathdiver

Full Access Member
Joined
May 18, 2017
Posts
19,100
Reaction score
25,022
Location
Treasure Coast, Florida
It can definitely be worth it under certain circumstances. I use that kit on all rebuilds where we're not replacing the TEHCM but as far as repairing a fault in one of the solenoids or malfunctioning pressure switch, that kit wont make a diff as it's not designed to fix those sort of faults. It's primarily designed to restore the positive seal for the pressure switches via replacement seals. Leaking seals can also cause flairs, etc but they'd have to very degraded (see it when the trans overheats, turns those seals hard thus they leak).

But if the TEHCM doesn't pass the resistance or voltage tests, the above kit won't restore it.

For those that haven't seen the pressure switch parts off the TEHCM, here's a pic:
View attachment 401424
Thanks for the clarification Nick! I'm really glad that you are here to learn us!
 

Forum statistics

Threads
128,781
Posts
1,805,310
Members
91,760
Latest member
MyCleftNut

Latest posts

Top