7AT Torque Converter Lockup Logic

dbfuru

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.

DarkJak

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.

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SouthArk370Z

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

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Tractionless

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

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