6L90 Torque Converter Failure Mitigation
Got in a playful argument about this.
I knew for a while a common failure of the 6L80s and 90s was for the torque converter to eventually shave itself.
A friend of mine in a high volume transmission shop sees this failure all the time - but unless they were fragrantly abused/neglected or had some QC issue they always had >250k miles on them when they went.
I believed there wasn't much you can do to mitigate this problem in software aside from not locking the TCC too early, not raise the pressures, and not have it slip at 30-50 RPM when its locked.
Whenever this comes up I just recommend regular fluid/filter changes, or if they're loosing sleep about it, have a reputable shop rebuild the damn thing with upgraded parts from sonnex, transgo, etc.
For normal driving I leave the TCC unlocked until 4th gear, reduce slip speeds under load to 0 while allowing 5-10rpm at low torque, and make an effort to keep the trans from shifting too frequently.
For towing I start to lock the TCC in 3rd gear, or 2nd if their tire/gearing setup is terrible, to avoid overheating when pulling up steep hills.
Common practice here seems to be leaving the TCC unlocked until 5th/6th gear.
The person I had this playful argument with believed this is "the secret to saving these transmissions".
While I'm sure there was a healthy amount of sarcasm behind that statement, it makes a good discussion point:
When you tune a customer who has a truck with a 6L80/90, do you do anything special specifically to prevent early failure of the converter? (besides disabling DoD on the 6L80s)
Is it really necessary to leave the TC unlocked all the way to 6th gear?
What do you tell the customer when they bring this up?
