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

[brandon9715]

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.

 

[notharry]

On another post myself and many others brought this up. I can see where one would want smoother shifts with regular driving. Unfortunately it uses nearly the same strategy on tow haul. My argument is that some converter or transmissions design cannot handle this strategy and the converter shudders. My 2010 F150 6r80 is one example. when the trans fluid gets near 200 the converter has the tendency shudder and vibrate the entire truck. My daughter has a 2008 Subaru and it does some of the same and has never shuddered once in 190000 miles. Ford, GM and probably others have struggled with this issue.

Further, at 20,000 mils the shuddering started in my F150. From new, the converter would lock after every gear change and sometimes shudder. Ford had a re-flash to repair this defect. Unfortunately, all it did was eliminate any converter lock-up except 6th gear. the shudder was still there in 6th. Of course this lowered my fuel mileage. Ford never solved this issue, called it normal and it still does the same thing to this day at 144,000 miles. Fluid change makes no difference, and neither did the addition of an additional cooler in the line. Ford states 100000 mile plus out of the fluid. Ive changed mine about 5 times already.