7AT Torque Converter Lockup Logic
 

Hi guys.

I've got a 2012 370Z with the 7AT. When I first had the car, when it was cold I had this strange issue where sometimes I'd pull up to a junction, and when I went to take off the revs would jump before the car suddenly kicked into gear.

It turned out to be low on fluid - it has been serviced before and whoever did the job obviously didn't follow the service procedures and underfilled it, so I serviced the transmission per the FSM, since then I've never had that issue.

However, all of my cars before this have been a manual so I have some questions for other 7AT owners about the torque converter lockup.

When I am in manual mode, usually in low speed/throttle input situations around town the torque converter will occasionally decide to unlock. So I might be in 4th gear enging braking around 3k rpm, then all of a sudden the rpms will drop to about 1k as the lockup clutch disengages. If I hit the accelerator the revs jump up and it locks back in. Not too big of a deal, happens in other gears too. Can make it a bit hard to do low speed powerslides, that's about the only trouble it gives me and the feeling that you don't really have 100% control. It always seems to get into a weird halfway locked/unlocked at about 2k rpm in 3rd gear. The sensation is like if I was coasting in a manual, then clutched in, then for some reason rode the clutch as I was re-engaging it and applying throttle

When I am driving spiritedly on the backroads I never have this happen, always feels like the converter is locked up and theres that direct connection.

Is this normal behaviour? I thought it was supposed to lock 100% in manual mode unless your engine speed dropped to a point where it would lug the engine whereby it will downshift. When the converter is locked there's never any sensation of slipping so I think the trans is ok.

I guess I just want some reassurance as to what the normal behaviour of these boxes is. My first auto and overall I am happy with it, and I've not driven any other auto Zs to compare.

I get similar behavior too at low rpms and low pedal input. I figured this was normal to try and prevent lugging, even though the car can still lug because the TC locks up if you full throttle it at low RPM.

The FSM may have a description of what's supposed to happen. Maybe not. Worth looking. Link in my sig.

Per FSM Lockup only happens when fluid temp is between 122-178*. Also lockup is prohibited when AT Fluid is too low.