6T70 Transmission Issues: And POSSIBLE FIX
So, I have a 2014 LT 3.6 with the 6T70 6-speed auto. I have read MANY discussions of troubles with this transmission. My Dealer (Deien Chevy in Trenton, IL) went to bat for me TWICE with GM after I had some symptoms, see below.
I purchased the car used in Jun2019 with 17K miles and some remaining warranty. Shortly thereafter I noticed an occasional very HARD upshift after passing at highways speeds. From say 50 mph, I would accelerate to 70 or 80 or whatever to pass. The car downshifted to pass, from 6th to either 5th or 4thgear. When I let off the gas to finish a passing maneuver, the upshift back to 6th gear was a VERY HARD THUMP. OH CRAP kind of hard. Alarmingly hard. It seemed to happen a bit more if the car was warmed up to full operating temps. For my car, that’s about 185 degrees. So, I took it in to the dealer and they were able to duplicate the problem.
So, my Dealer called GM to investigate. They wound up replacing the “TCM and valve body” under full warranty. I don’t have details on this repair, but it did not solve the problem. So, a few weeks later, I called the Dealer again and they tried again with GM.
This time the problem HAS BEEN ELIMINATED. This is the first time I can read where a 6T70 problem was stopped without an aftermarket tune, so I thought I should share. Below is the dealer writeup of the repairs. I asked them for as much detail as they could manage. I share this now in the hope that this is useful for some of you.
So, I have a 2014 LT 3.6 with the 6T70 6-speed auto. I have read MANY discussions of troubles with this transmission. My Dealer (Deien Chevy in Trenton, IL) went to bat for me TWICE with GM after I had some symptoms, see below.
I purchased the car used in Jun2019 with 17K miles and some remaining warranty. Shortly thereafter I noticed an occasional very HARD upshift after passing at highways speeds. From say 50 mph, I would accelerate to 70 or 80 or whatever to pass. The car downshifted to pass, from 6th to either 5th or 4thgear. When I let off the gas to finish a passing maneuver, the upshift back to 6th gear was a VERY HARD THUMP. OH CRAP kind of hard. Alarmingly hard. It seemed to happen a bit more if the car was warmed up to full operating temps. For my car, that’s about 185 degrees. So, I took it in to the dealer and they were able to duplicate the problem.
So, my Dealer called GM to investigate. They wound up replacing the “TCM and valve body” under full warranty. I don’t have details on this repair, but it did not solve the problem. So, a few weeks later, I called the Dealer again and they tried again with GM.
This time the problem HAS BEEN ELIMINATED. This is the first time I can read where a 6T70 problem was stopped without an aftermarket tune, so I thought I should share. Below is the dealer writeup of the repairs. I asked them for as much detail as they could manage. I share this now in the hope that this is useful for some of you.