[arpad_m]

Originally Posted by metroplex

I just wanted to add that back around 2001, I had a conversation with a Ford powertrain engineer who explained why the Torque Converter shudder happens and how to prevent it from happening with a tune. Keep in mind this is 2001, so we were discussing transmissions made during that era and the AOD/AODE before that (late 80s to early 90s) so the TCC shudder is not a new problem. But this is 110% applicable to this day.

He explained the TC lockup clutch as a gun with a bunch of bullets. Once those bullets are used up, the shudder starts to happen. The TC clutch gets worn out from the constant steady state slippage that occurs. Using extra friction modifiers like Dr No Shudder or other bottles will be a band-aid fix but the permanent fix is a new TC lockup clutch.

So his tunes back in 2001 would zero out the steady state slip, which is what the OP is talking about here. From 2001, I'd always zero out steady state slip in my own automatic trans tunes.

The reason the OEMs have this slip is really for driveability. The average car consumer does NOT want to hear or feel any driveline clunking. The Torque Converter is a good damper for this.

I used to be able to tweak the tip-in on the 4R70W to prevent the TCC from unlocking so it basically handled like a manual trans - where after decel, tip-in would result in a "clunk" from the TCC staying lockup and the driveline slop working its way to the cabin. I haven't been able to figure this part out on the newer Ford transmissions, and keep in mind GM/Ford has some jointly developed transmissions (6F55/6T7x, 10R80/10L90, 8Fxx/9Txx etc...)

This is very interesting, thank you for sharing, metroplex.

My 8L90 has been tuned since about 2000 miles on the clock, slip tables zeroed, trans preemptively flushed twice, on the correct fluid since about March 2019. Now it possible that I already am desensitized, but I'm simply not experiencing any clunk in those decel, then tip-in situations except when the trans fluid is very cold and I've just finished coasting downhill. Even then it isn't horrendous per se.