6L80E Rough Shift 1-2 and 2-1

[BeauDuke45]

Hey folks,

Owned my 2012 SSV for a few weeks now and loving the heck out of it. Moved up from my 97 tahoe.

Here is my situation, the truck has a slight rough shift from 1-2, both when warm and when cold, but it’s not constant. The shift from 2-1 feels a little rough and like you are getting some engine after the shift.

Took it to the dealership for the remote start (AP8 code came with) and had them glance at the trans, said it needs a rebuild or replace. Back in 2016 the sheriff’s department took it in for a rebuild as well. It’s got 169k on it.

Thoughts?


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[swathdiver]

Hey folks,

Owned my 2012 SSV for a few weeks now and loving the heck out of it. Moved up from my 97 tahoe.

Here is my situation, the truck has a slight rough shift from 1-2, both when warm and when cold, but it’s not constant. The shift from 2-1 feels a little rough and like you are getting some engine after the shift.

Took it to the dealership for the remote start (AP8 code came with) and had them glance at the trans, said it needs a rebuild or replace. Back in 2016 the sheriff’s department took it in for a rebuild as well. It’s got 169k on it.

Thoughts?


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Well, what does "rough shift" mean Beau? Jerking? Hard? Bang? Same thing when slowing to a stop? It's normal to feel it run back down through the gears to first, especially the 2-1 shift since the ratio is so steep.

The best part of my Blackbear tune was how he improved the performance of the transmission, night and day difference and made it like a different vehicle and for the better!

 

[BeauDuke45]

Well, what does "rough shift" mean Beau? Jerking? Hard? Bang? Same thing when slowing to a stop? It's normal to feel it run back down through the gears to first, especially the 2-1 shift since the ratio is so steep.

The best part of my Blackbear tune was how he improved the performance of the transmission, night and day difference and made it like a different vehicle and for the better!

Hey Swathdiver,

The shift from 1st to second feels lagged occasionally, but mainly feels like it shifts into second that it lurches or pulls you forward. I’ll work on a more detailed description when I am heading to the office tomorrow morning.

I’ll also lol into the blackbear tune.


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[BeauDuke45]

Hey Swathdiver,

The shift from 1st to second feels lagged occasionally, but mainly feels like it shifts into second that it lurches or pulls you forward. I’ll work on a more detailed description when I am heading to the office tomorrow morning.

I’ll also lol into the blackbear tune.


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I forgot, when shifting from 2-1, you can feel the shift somewhat, but it more feels like you are getting some engine brake after the shift, like the RPM’s were too high before it down shifted.


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[swathdiver]

I forgot, when shifting from 2-1, you can feel the shift somewhat, but it more feels like you are getting some engine brake after the shift, like the RPM’s were too high before it down shifted.

When I'm coasting to a stop and going slow, the 2-1 shift is almost like going from 3rd to 1st in a stick shift car if doing so at about 5-10 mph. I consider that normal, especially with 3.42 gears. 1st gear is like a granny gear, very steep to get moving while towing a heavy load.

 

[petethepug]

Welcome & congrats on getting into the GMT 900. Little diff huh? We really thought hard about moving over from the 800 to 900 series Denali in ‘14. Never looking back now. Doesn’t seem like like a fresh rebuild from a shop that serviced a SSV trans would be due again. I’m thinking trans service, not replace. Check the harness connections or the ez stuff first. I’m not sure which harness connection is for the 1-2, 2-3 shift though.



“4L60E trans use 2 shift solenoids, initially called Shift Solenoid A & Shift Solenoid B, later changed to comply with OBD II (On Board Diagnostics revision 2) regulations to 1-2 Shift Solenoid & 2-3 Shift solenoid. By activating and deactivating the solenoids in a predetermined pattern by the PCM, 4 distinct gear ratios can be achieved.”


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[BeauDuke45]

Where would I find the location of those harnesses in the diagram?

It’s a world of difference from the OBS chevy’s for sure!

Drive home and to work today the trans shift from 1 to 2 feels like it lurches forward a little. 2nd to 1st does feel like a manual downshifting from 3rd to first like another poster mentioned.

Investigating the harness and mulling over a tune from Black bear performance. Trying to rule out the cheaper and easier stuff first.

On a bright side, the alpine I’ll-107 that I out in over The Weeknd for the heady it is spectacular! Time to get the back camera finished up, fix a buster exhaust bolt, and do the drivers side engine mount!


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[BeauDuke45]

Quick update on the rough shift for my 2012 tahoe with a 6L80e.

I did a bunch research and digging, and decided to go with getting a tune. I tried a few options, such as removing the fuse the the TCM and turning the vehicle to 'accessory' for 10-15 minutes, then plugging the fuse back in for the transmission to reset and learn the shift points: unsuccessful.

Research also had me looking into a shift kit/solenoid upgrade, but i didnt want to go down that route just because i wasn't sure that would solve the issue and didn't want to risk making the shifts worse.

I spoke/interviewed the tuner about the issues I was having and he said that he has worked on several of these tahoes and the 6L80E transmissions. he stated the experiences i have been having are common and are due to the new format of the transmission after driving a 4L60e for so long. The jolt I was feeling from 1-2 was pretty common, but a little more pronounced on my Tahoe and are due to the torque converter locking up when shifting from 1-2. The shift from 2-1 was a function of the programming for these trucks to use the transmission to help slow down the vehicle instead of just the brakes (trying to save brake wear).

All in all, the tuner was able to go in and smooth out the shifting dramatically and I am stocked to drive the vehicle now, as before i was slightly frustrated. Got to love the updated electronics and programming used on these transmissions! I'll defer to someone else on the forum for a better explanation on the details, I like to learn as much as i can about my vehicle, so more information is always better!

If anyone needs the name of a good tuner in the Denver area, American Intense Racing was who i used and was referred too. Was able to get everything tuned up in about 2 hours. Just call ahead and schedule a session with him! Cost me about $325.

 

[BeauDuke45]

another quick update on this one. The tune did not help the shifting issue. My father in law and I did fix the busted as hell motor mount, and that did help somewhat. Hopeful he can do some diagnostics today (teaches auto mechanics at a community college and has the snap-on tool he brought from work).

More to come.....

 

[swathdiver]

another quick update on this one. The tune did not help the shifting issue. My father in law and I did fix the busted as hell motor mount, and that did help somewhat. Hopeful he can do some diagnostics today (teaches auto mechanics at a community college and has the snap-on tool he brought from work).

More to come.....

Get a subscription to AllDataDIY and use your Father-in-Laws scan tool hand in hand with the manual to trouble shoot the symptoms. Then consider buying a Tech-2 for the vehicle.