3-4 gear shift followed by RPM drop 6R80 and 6F35

[belbers9715]

Hello all,
I used to own a Ford Fusion with the 6F35 and noticed the same thing happen on that as what is currently happening with my F150 with 6R80. As I accelerate and shift through the gears, the tranny shifts to fourth gear and shortly after the shift, the rpm will drop as I accelerate. To be clear, the shift to fourth gear occurs, normal rpm drop due to higher gear, rpm begins to climb, then rpm drops as speed increases. What is the cause of this? Doesn't seem logical to me, as how can my speed increase without rpm increasing while staying in the same gear? If this was tranny slip, rpm should increase as my acceleration stalls. Both the 6F35 and 6R80 transmissions have had regular fluid changes with Motorcraft Mercon LV.

 

[SubieRubyRoo]

TCC lockup

 

[dnewton3]

It's not just Fords; many brands do this. My 2023 Lexus ES350 does the same thing; locks and unlocks the TC based on demand of load, rpm, etc.

 

[vpr5703]

Hello all,
I used to own a Ford Fusion with the 6F35 and noticed the same thing happen on that as what is currently happening with my F150 with 6R80. As I accelerate and shift through the gears, the tranny shifts to fourth gear and shortly after the shift, the rpm will drop as I accelerate. To be clear, the shift to fourth gear occurs, normal rpm drop due to higher gear, rpm begins to climb, then rpm drops as speed increases. What is the cause of this? Doesn't seem logical to me, as how can my speed increase without rpm increasing while staying in the same gear? If this was tranny slip, rpm should increase as my acceleration stalls. Both the 6F35 and 6R80 transmissions have had regular fluid changes with Motorcraft Mercon LV.

When I had a Fusion with the same transmission it did the same thing. From the data I saw on my OBD2 reader, what is happening is that right as the transmission shifts the torque converter is unlocked. After the shift the converter is slowly locked back up. This provides a smoother shift feeling. The strategy is common among other brands as well as dnewton said.

 

[bullwinkle]

The torque converter lockup clutch (TCC) is controlled by a pulse width modulation solenoid (PWM)-it applies the clutch gradually instead of all at once. If you tap the brake with your other foot the TCC should drop out again & gradually reapply.

 

[dumkid]

If you let off the throttle slightly the rpm should stay almost the same. If you let off fully the TCC will unlock and your engine will drop near idle.

Many new transmissions will lock and unlock the TCC between every gear effectively giving you twice the gear ratios. Old transmissions would only lock up in the top one or two gears and weren't as smooth about it.