Why doesn't the torque converter lock in 1st and 2nd gear?

Why doesn't the torque converter lock up in 1st and second? Wouldn't there be less heat buildup if Toyota made it lock in 2nd?

 

What is the year?
What is the model.... 2wd, 4wd, and engine ?

 

I believe it’s to prevent jerky shifts. Typically you are accelerating through 1st and 2nd, not driving around in those gears for hours, so lockup isn’t really needed, and smoothness is the priority.

 

This is on a 2018 3.5, 4wd. I suspect this is for all v6 3rd gens but I could be wrong. Just curious why Toyota made this decision.

 

I dont know the actual engineering reasoning but I know on (most) fords it doesn't lock until you hit approx 40 mph. I assume its so that at lower speeds its slipping somewhat so it feels smoother

 

Because you usually aren't cruising for long periods of time in those gears. And the lower gearing doesn't stress the drive train like 4th and 5th

 

We are all scratching our heads wondering why Toyota made the choices they did for this 3rd gen.
I can't wait for the 4th gen threads.

 

Once Toyota started early locking we suffered shudders like crazy.

I’d stop it from 3rd gear lock up as well if I could.

4th gen will be complaining they can’t hit 8th gear.

 

8th gear
It can barely hit 6th as it is.
Besides having to drive 30 miles to actually see the mpg that was printed on the window sticker.

 

Curious abot this..
Significant time - even hours- is spent in 1st & second gears in certain off road scenarios, no?

 

You can in VFtuner. When you say "shudder" what do you mean?

 

What do you mean? You want 3rd to not lock or do you want 2nd to lock?

 

The full tc lock control is not available in Vf tuner. The full lock is controlled by pressure setting somewhere in guts of tranny control unit
Only SLU solenoid control is available, which is "flex" lock (partial lock)

 

It wouldn't work as well, locking the converter clutch would eliminate the torque multiplication of the converter.

The torque multiplier effect means that a vehicle equipped with a torque converter will output more torque to the drive wheels than the engine is actually producing. This occurs while the converter is in its “stall mode” (when the turbine is spinning considerably slower than the pump) and during vehicle acceleration.

Torque multiplication rapidly decreases until it reaches a ratio of 1:1 (no torque increase over crankshaft torque).

A typical torque converter will have a torque multiplication ratio in the area of 2.5:1. The main point to remember is that all properly functioning torque converters do indeed multiply torque during initial acceleration.

Torque multiplication does not occur with a manual transmission and is compensated for with heavier flywheels, higher numerical gear ratios, and higher launch rpm.



Learn more here: https://www.gandmtransmissions.com/transmission/

 

The torque converter is your friend in off road scenarios, offering “infinite gear reduction” at the price of heat. That’s why nobody wins any off road competition involving technical driving in a standard transmission vehicle.

If you are spooling up your engine and racing around in 2nd gear, you should be switching to 4Lo.

 

Pretty sure Toyota forgot to put a torque converter in my minivan truck.