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Discussion Starter #1
Hi,

I've noticed that the transmission in these cars (6T70) likes to be in the lowest gear possible at all times. When easing off the gas around 35-40 MPH I have been hearing a slight groan noise as it upshifts 4-5. At the exact same time I see about a 200 RPM rise on the tach before the needle falls from 2000 down around 1000 RPM which seems to almost lug the engine. I'm not sure if the surge is a slip of some sort or the torque converter unlocking. I would miss it if I didn't stare at the tach, as it is very subtle. If I accelerate faster causing it to shift over 2000 RPM there is no surge or groan noise. A higher RPM shift 4-5 is completely smooth.

Fluid has been changed and level is correct. Thoughts?
 

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Discussion Starter #5
I have been using the Torque app with an OBD adapter to monitor the transmission sensors while driving. I noticed a few interesting things. It seems that the torque converter clutch (TCC) is set up to go into lockup in as low as 3rd gear during slow acceleration. I watched the TCC slip readout during the 3-4 shift consistently show a bump to ~120 RPM slip as the converter unlocks and re locks at the shift. 4-5 unlocks, slips to 170-180 RPM, then re locks. 5-6 has relatively little slip. 1-2 and 2-3 shifts usually have the TCC already unlocked before and after the shift so the shifts are smoother. Hard acceleration leaves the converter unlocked right into the 4-5 shift with lots of slippage which is probably why hard acceleration feels like smoother shifts.

I did some reading about pulse width modulation/constant slip which seems to be used in this transmission. Apparently torque converter slip is electronically controlled to smooth the shifts and there is always a small amount of slip. My last few cars were manual transmission and the cars I drove before that were older and apparently had a full lock or full unlock converter, which is the older technology. Maybe I'm just noticing the different TCC control strategy.

I'll keep the shift kit in mind if anything seems to get any worse. Another interesting find with Torque was that my transmission fluid temperature never makes it over 160 on my daily commute. I've checked the level cold (barely touching dipstick) so I should be good there.

Thanks.
 

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same issues, local trans shop stating tcc is damn near shot, trans rebuilt required. 3k smh,,
but at 175K miles its time is guess,,
 
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