6L80 soft shifts under heavy load

Ive checked all of the inertia and torque adder settings. Im wondering if I have a bad valve body. Under normal acceleration, gear changes are firm and quick. I noticed the other day under about 75% throttle the 1-2 and 4-5 was very soft. I was wondering if the 1-2 was going to shift. My trans has the ZL1 converter, and full Zip kit and raybestos clutches. I double checked all of my settings, even though it hasnt been adjusted in about 8 months or so. Nothing else has changed. Could I have a leaking valve in my valve body or a check ball shrinking? anyone else dealt with this? Vehicle is a 15 Silverado 5.3/6L80

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Originally Posted by Estep40511

Ive checked all of the inertia and torque adder settings. Im wondering if I have a bad valve body. Under normal acceleration, gear changes are firm and quick. I noticed the other day under about 75% throttle the 1-2 and 4-5 was very soft. I was wondering if the 1-2 was going to shift. My trans has the ZL1 converter, and full Zip kit and raybestos clutches. I double checked all of my settings, even though it hasnt been adjusted in about 8 months or so. Nothing else has changed. Could I have a leaking valve in my valve body or a check ball shrinking? anyone else dealt with this? Vehicle is a 15 Silverado 5.3/6L80

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I would start with a pressure gauge to see if the transmission is making the line pressure the TCM is commanding.

Checked the line pressure. is good. Trans is only coming up on 3 years old. I have changed my final shift times and adjusted the inertia factors slightly. Also the torque adder tables. Seems to have helped the 1-2, but was wondering if someone could look at my log and see if I have any other issues or things to adjust?

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Originally Posted by Estep40511

Checked the line pressure. is good. Trans is only coming up on 3 years old. I have changed my final shift times and adjusted the inertia factors slightly. Also the torque adder tables. Seems to have helped the 1-2, but was wondering if someone could look at my log and see if I have any other issues or things to adjust?

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I see no log posted anywhere in this thread.

Here is the log.Attachment 152749

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Originally Posted by Estep40511

Here is the log.Attachment 152749

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The 2-6 brake is slipping big time under load during the 1-2 shift, the computer tries its best to fix the issue but it just can't. Most likely the pack is burnt unfortunately.

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Originally Posted by TransGo Robert

The 2-6 brake is slipping big time under load during the 1-2 shift, the computer tries its best to fix the issue but it just can't. Most likely the pack is burnt unfortunately.

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I was wondering about that being the case. Fluid is nice and pink and smells new. no burnt smell at all.

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Originally Posted by TransGo Robert

The 2-6 brake is slipping big time under load during the 1-2 shift, the computer tries its best to fix the issue but it just can't. Most likely the pack is burnt unfortunately.

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I was hoping a check ball or valve in the valve body.

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Originally Posted by Estep40511

I was wondering about that being the case. Fluid is nice and pink and smells new. no burnt smell at all.

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Surprising it does not smell burnt considering just how badly the 2-6 is slipping. By the way, when you get it rebuilt I highly recommend you get the technician to install our 6L80-TOW&PRO Reprogramming Kit™ in there, it drastically increase the 2-6 capacity and overhaul makes that unit really come alive and last.
https://transgo.com/product-details/6l80towpro/

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Originally Posted by TransGo Robert

Surprising it does not smell burnt considering just how badly the 2-6 is slipping. By the way, when you get it rebuilt I highly recommend you get the technician to install our 6L80-TOW&PRO Reprogramming Kit™ in there, it drastically increase the 2-6 capacity and overhaul makes that unit really come alive and last.
https://transgo.com/product-details/6l80towpro/

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gotcha. im a tech for GM, so Ill be rebuilding it myself again. I have the Zip kit in it now. what are the differences in that and the TransGo kit? also, is the 2-6 slipping all the time or just during the shift?

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Originally Posted by Estep40511

I was hoping a check ball or valve in the valve body.

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Not going to be a checkball issue on the 1-2 unfortunately.
Only four possibilities:
1- Not enough line (you said you checked and confirmed it was going up to the commanded 260-270 psi range under load)
2- A mechanical issue with pressure control solenoid #4 (that would also cause a 5-6 flare and you did not mention that so I ruled it out). It is also very rare for that solenoid to fail.
3- A command issue (it all looks great on that front in the log, the 2-6 is just not doing what it is asked to do)
4- A compromised 2-6 brake seal/piston/frictions plates

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Originally Posted by TransGo Robert

Not going to be a checkball issue on the 1-2 unfortunately.
Only four possibilities:
1- Not enough line (you said you checked and confirmed it was going up to the commanded 260-270 psi range under load)
2- A mechanical issue with pressure control solenoid #4 (that would also cause a 5-6 flare and you did not mention that so I ruled it out). It is also very rare for that solenoid to fail.
3- A command issue (it all looks great on that front in the log, the 2-6 is just not doing what it is asked to do)
4- A compromised 2-6 brake seal/piston/frictions plates

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actually, I do have a intermittent 5-6 flare, usually after the trans is up to temp. And like I said, its an intermittent thing. Should I take the TCM out and air check the solenoids.

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Originally Posted by Estep40511

actually, I do have a intermittent 5-6 flare, usually after the trans is up to temp. And like I said, its an intermittent thing. Should I take the TCM out and air check the solenoids.

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You would need specialized aka $$$ equipment to test the solenoid. You would have to either throw a TEHCM to see if it fixes it but I say 95% of the chances it is not going to be that solenoid just based on the pattern of failure on those.

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Originally Posted by Estep40511

gotcha. im a tech for GM, so Ill be rebuilding it myself again. I have the Zip kit in it now. what are the differences in that and the TransGo kit? also, is the 2-6 slipping all the time or just during the shift?

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Apples and oranges as far as the kits are concerns, the Zip Kit is more like our Shift Kit? where it addresses known issues with the unit. Our TOW&PRO kit on the other hand is the only kit available that increases the torque capacity of the friction elements and shorten the shifts using our Patented technology that makes it possible to do so without having the computer undo all the changes you make hydraulically in the unit.

In your short log, it only slipped bad during the 2nd 1-2 shift when you were under more load. You can't really feel that by the seat of the pants since nothing releases on the 1-2 unlike during a 5-6 shift, so you don't get a flare, it just makes it feel like a late shift. But the whole time it is ramping up the solenoid trying to get it to shift and it remains in 1st gear, the 2-6 is actually slipping. Here's a screenshot to help illustrate it better. I put in the two red boxes the solenoid command and the calculated ratio during the long drawn out 1-2 shift. You can see that yellow trace for the solenoid command is just ramping up and ramping up gradually hoping to get the 2-6 to finally grab and start slowing down the rotating clutch hub but nothing happens. Then where I put the two orange circles you can see the computer had enough and takes drastic action bumping up the pressure to the 2-6 and at the same time you can see the ratio finally changing in a bumpy kind of way (that's called a slide bump in transmission lingo). After that no problem, it is holding steady as you can see from the yellow ratio trace at the bottom staying perfectly flat. I hope this helps.
Attachment 152757

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Originally Posted by TransGo Robert

Apples and oranges as far as the kits are concerns, the Zip Kit is more like our Shift Kit? where it addresses known issues with the unit. Our TOW&PRO kit on the other hand is the only kit available that increases the torque capacity of the friction elements and shorten the shifts using our Patented technology that makes it possible to do so without having the computer undo all the changes you make hydraulically in the unit.

In your short log, it only slipped bad during the 2nd 1-2 shift when you were under more load. You can't really feel that by the seat of the pants since nothing releases on the 1-2 unlike during a 5-6 shift, so you don't get a flare, it just makes it feel like a late shift. But the whole time it is ramping up the solenoid trying to get it to shift and it remains in 1st gear, the 2-6 is actually slipping. Here's a screenshot to help illustrate it better. I put in the two red boxes the solenoid command and the calculated ratio during the long drawn out 1-2 shift. You can see that yellow trace for the solenoid command is just ramping up and ramping up gradually hoping to get the 2-6 to finally grab and start slowing down the rotating clutch hub but nothing happens. Then where I put the two orange circles you can see the computer had enough and takes drastic action bumping up the pressure to the 2-6 and at the same time you can see the ratio finally changing in a bumpy kind of way (that's called a slide bump in transmission lingo). After that no problem, it is holding steady as you can see from the yellow ratio trace at the bottom staying perfectly flat. I hope this helps.
Attachment 152757

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Thanks for the input! Ive already ordered all the clutches in a kit (GM part), a 2-6 assembly and a 1-2-3-4 clutch hub assembly. Ill probably replace the pump and housing with rotor vanes etc. might as well while I have it apart.lol

You should post the tune file. Very seldomly do I see a 6l80 setup correctly on here.

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Originally Posted by Estep40511

Thanks for the input! Ive already ordered all the clutches in a kit (GM part), a 2-6 assembly and a 1-2-3-4 clutch hub assembly. Ill probably replace the pump and housing with rotor vanes etc. might as well while I have it apart.lol

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Sounds good, if you end up getting our TOW&PRO kit send us an email at [email protected] (I answer those 99% of the time) and i'll walk you through a couple of like things you'll have to do to make it work with the other kit you already have in there. And for what it is worth, I see no need to replace the bell/rotor/vanes if your pressure is good at idle hot and if nothing is scored in there when you take it apart.

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Originally Posted by Alvin

You should post the tune file. Very seldomly do I see a 6l80 setup correctly on here.

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Here ya go.



Attachment 152758

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Originally Posted by Alvin

You should post the tune file. Very seldomly do I see a 6l80 setup correctly on here.

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Hoping it can possibly be adjusted.

I'm not a fan of all the pressure changes.

What happens is the trans will shift faster from the pressure but undershoot shift times because of that.. This drives the adaptives crazy and all of a sudden its pulling shift time/pressure globally (like a long term trim) because sometimes it was too fast. This shows up as randomly shifting super soft / shift flair. The issue can take months to show up.

I'd put back everything to stock other than

*Shift timing Torque adder Normal and special. All else go back to stock
*Downshift torque adder normal and special.

After you do this.. This is going to sound weird. but hit every button in the scanner bi directional controls around shift fast reset, adapt, etc. After you do this the trans will not have forward gears or reverse.. It will be in a neutral stuck state. Then write entire the tcm file. This is the easiest full proof way of clearing all the adaptives..

Give it a few days of driving before making a judgment.


People don't remember this or know this maybe but with 6l80's and HPtuners we got shift schedule, then later got some crude TM settings, then much later shift pressure and inertia factor, then finally all the shift time stuff. We didn't get what you see now all at once. It took a long time for all that to be defined. drip drip drip.

All these things were separated by maybe years. My point is we started tuning them just like the old stuff via TM and pressure. The cars would come back with shift flairs or just not the same as when I left them. Shifts were inconsistent over time. Leaving that stuff mostly if not all stock and adjusting the targeted shift times is where it's at.. I get consistently good results long and short term this way.

I can still get a uncomfortably hard shifts without touching pressures... Even with full TM.