Flex lock-up/torque converter question

Kind of a random question, but can someone explain this to me?

I'm trying to better understand the S mode shifting vs D. I do understand S mode is simply a gear limiter. I get that.

But as I dug deeper, it's not a simple as that. There's more to it- and I think it might account for why some people think shifting is smoother throughout the stack when running in S mode.

As I interpret this chart- flex lock-up (is this the same as the torque converter?) isn't happening in 3rd and 4th gear when in S4. So... smoother shifting "feel" as you go through the gears?

So, what's actually happening here? Hoping someone can shed some light. Anything I say is pure speculation, as I know nothing about any of this. I just thought the chart was interesting and might bring to light something a lot of us didn't know before.

 

If you guys test drive a late model Tacoma you’ll be overjoyed to get back in the 4Runner. The Tacoma shifts way too soon and seems always locked from 3 on up, at any speed. My 4Runner does lug along in 5 as often as it can but the engine is more up to it. I suspect the converter is locked as soon as possible. Most every vehicle nowadays is like that. Kind of a shocker coming from a diesel pickup and an old 3spd auto TJ. The 4runner and especially the Tacoma would be much more enjoyable drive if that convertor wasn’t locked until 45-50 mph and never in 1-3.

 

Yeah I know exactly what you're describing here. If you think it's noticeable in the 4runner, it's like 10x as bad in the 3rd gen Tacoma. 2nd gen Tacoma is similar to 5th gen 4runners (very tolerable, imo).

The Tacoma guys call it a "stumble". And it's seemingly worse in some trucks than others. They actually issued a TSB for some of the 3rd gen Tacoma's.

When I had my 2018 Tacoma, I found that it could be avoided by simply accelerating much more slowly. But my thought was that you shouldn't be forced to accelerate slowly in order to avoid the feeling of a loss in power (early shift).

 

Can someone explain to me what the "flex-lock up" or torque converter is?

And why would they stop it from happening when in S4?

 

Definitely an all around different feel when driving in S4. It feels like YOU are (or can be) in control of shifting based on speed/throttle input. Its predictable.

But in D you can definitely feel that it's mapped for economy. I'm not complaining. It's very similar to my 2nd gen Tacoma's.

 

Where did you get this chart from?

 

I believe I copied it from somewhere else on the forum.

 

When I’m in S4 my sc3 says my torque converter is locked when I’m at like 45-50? On that diagram is shows lockup but on deceleration?

 

4. Flex Lock-up Clutch Control
In the low-to-mid-speed range, this flex lock-up clutch control regulates the solenoid valve SLU to provide an intermediate mode between the ON/OFF operation of the lock-up clutch in order to improve the energy transmitting efficiency in this range. As a result, the operating range of the lock-up clutch has been increased and fuel economy has been improved. The flex lock-up clutch control operates in the 3rd, 4th and 5th gears in the D position and S5 range, 4th gears in the S4 range. Even when the vehicle is decelerating (the accelerator pedal is released), the flex lock-up clutch control operates. Therefore, fuel-cut area of the engine has been expanded and fuel-economy has been improved.

So it sounds like a lower speed lock-up supplement to improve mileage and feel. It is not the primary TCC lock control which still remains a mystery lol.


Lock-up Timing Control-The ECM sends current to the solenoid valve SLU based on signals from various sensors and engages or disengages the lock-up clutch.

Flex Lock-up Clutch Control-(See Page CH-31) Controls the solenoid valve SLU, provides an intermediate mode for when the lock-up clutch is between ON and OFF, increasing the operating range of the lock-up clutch to improve fuel economy

 

A related question: Can anybody explain the difference between D and S5? Is there a difference? In the OP's chart, they are listed together so that says at least the flex lock up characteristic is identical for each of them.

 

I mean D is 5th gear. Using "S" doesn't change any parameters and is simply a single detent for highest gear auto upshift just like regular downshifting. No one really knows what S means but I could have sworn it was listed as "sequential" in the last generation Celica.

 

The diagram pertains to partial lockup (aka "Flex"). Traditional lockup and unlocking still occurs.

 

Are there a separate pids on the scan tools for flex and regular locks or just one?

 

^Never cared enough to look. The A750 has an easy life in the 5th gen compared to hauling early 2nd gen V8 Tundras and foreign market diesel Prados. If you have a local OTT or Yotawerx tuner, you can ask them, since the tunes can control partial lockup behavior.

 

I have configured a display for “TC Lock Up” in my torque app. However, this comes only active in 4th and 5th gear when there is little action on the throttle and on higher speeds.
Seems to be the "traditional" lock for the Torque Converter and is it correctly only active in 4th and 5th gear?
As i understand it now, flex lock is an additional clutch / function?

 

From what has been explained, it seems that it’s function, not an additional clutch.

 

S4 is just manual shift and it will manually shift into 5th. S4 is what I use towing with Economy mode off. You don't really want to be pulling a load in 5th. I couldn't find anything in the manual about towing specifics for transmission. My older 4sp ones you always locked the OD and towed in 3rd. Better gears, less power, pulled great then. I use S4 manual on hilly, curvey roads to upshift/downshift instead of a lot of braking.

 

I've heard several people say that the manual states the obvious to tow in S4, I always do but it is nowhere in my '23 manual.

 

Yeah I couldn't find find anything about it. I guess 5th is so light, any pedal load sends it to 4th anyway in D. I didn't realize it shifted to 5th in manual for a while.