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Old 07-05-2007, 01:54 AM   #1
rickst29
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Lightbulb Driving Toyota/Lexus SUV Automatic Transmissions

This information applies to recent 4Runner, Sequoia, and GX-470 vehicles, as well as the equivalent pickups models with 5-speed automatics.
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You need to watch the tach and learn to identify when the torque converter has unlocked itself. When this happens, the torque converter will churn the ATF, causing the tranny temp to rise. If allowed to continue, this can overheat and damage the tranny.

During the first second (or two) after your Tranny has changed gears, you SHOULD see the RPMs drop off by about 150-200 (while holding constant speed). This occurs when your torque converter "locks up", which it does to improve efficiency and keep the ATF temperature down. When the converter is "locked", there is much less stress on the the ATF, because it isn't being called upon to do as much of the energy transfer anymore.

A sudden rpm jump of 200-300 indicates the converter has unlocked. This will happen when you need more torque to maintain speed, such as when climbing a grade or towing into a headwind. If the converter stays unlocked for any long period (over a minute or two), manually shift down (from overdrive to 4th, or from 4th to 3rd), which will allow the engine speed to rise and the converter to lock up again.

Learn to recognize lock and unlock, and adjust your driving (with and without the Trailer) so that you're driving locked almost all the time, with only a few moments of "unlocked" time when you (or the vehicle itself) actually shifts. BTW, running "locked" in 3rd at higher RPMs gets BETTER gas mileage than running "unlocked" in 4th-- when unlocked, a lot of the engine torque is wasted, generating heat in the ATF fluid instead of driving the tires. "Locked" 4th gets better MPG than "unlocked" 5th for the same reason.
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Of course, it's a good idea to downshift ahead of time when you see a hill ahead that you KNOW the vehicle won't be able to handle without unlocking (if you stay in your current gear). Do your downshift shortly before you start climbing the grade.
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Also, of course, learn to manually downshift on long downgrades to avoid brake fade. The rule of thumb is to choose a lower gear that'll let you descend the grade while maintaining your speed without using the brakes. NEVER coast in neutral with a trailer!
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Old 07-05-2007, 03:54 PM   #2
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Quote:
Originally Posted by rickst29 View Post
This information applies to recent 4Runner, Sequoia, and GX-470 vehicles, as well as the equivalent pickups models with 5-speed automatics. .. You need to watch the tach and learn to identify when the torque converter has unlocked itself ... Learn to recognize lock and unlock, and adjust your driving (with and without the Trailer) so that you're driving locked almost all the time
Rickst -

This is good advice (read VERY IMPORTANT) for ALL automatic transmission vehicles. I have tried to explain that recognition process in the past, and have failed miserably. The writeup you present is clear and concise. May I ask the source?

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Old 07-05-2007, 05:24 PM   #3
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Default I adapted from a Karl Haug post....

on http://www.toyota-4runner.org, threadid=28447#post242416.

I don't think that I can paste my link, because it's full of auto-login PHP sessionID stuff. The "After 1-2 seconds...." paragraph is completely mine, he didn't talk about the lock-up process at all. The original version also talks only about shifting between OD and 4th, but the advice is applicable to shifting 4th-3rd as well.

(And maybe 3rd-2nd too. I haven't been on a steep enough grade to ever take a good look at whether there's lock-up in second. But I'll SWAG that there probably *IS*, even without invoking the special off-road gearing and differential lock features of my "Sport" model.)

Yeah, I'm not a writer, the two GOOD paragraphs are not by me.
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Old 07-05-2007, 05:55 PM   #4
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This does not apply to those who have the "tow/haul" button like that on my Jimmy. The "tow/haul" button takes care of that for you since it changes the shift points and minimizes the time when the torque converter is not locked up.
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Old 07-06-2007, 09:53 AM   #5
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Good point, Jim. I missed that one. Thanks.

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Old 07-28-2007, 01:05 AM   #6
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Earlier Toyota 4 speed transmissions will lock the converter if you turn off the overdrive, which shifts to 3rd (locked).

A normal automatic down shift from 4th to 3rd places the tranny in 3rd with the converter unlocked when under heavy load which would heat the ATF just as being in overdrive with the converter open.
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Old 08-08-2007, 12:23 AM   #7
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A normal automatic down shift from 4th to 3rd places the tranny in 3rd with the converter unlocked when under heavy load which would heat the ATF just as being in overdrive with the converter open.
Yes, sometimes (even on the more powerful current models) you have to CHOOSE the lower gear by hand (in this case, choose 2nd). But with my '07 4R, and my deceased (RIP ) '05, a downshift to 3rd nearly always provides enough RPMs and engine torque/power to allow lockup.... except on extreme grades at altitude. But of course, My 2619 probably isn't even 4000 lbs., either.

Watch the RPMs like a hawk when it shifts, and SEE the drop for "lockup". The bigger RPM change (upwards) for unlock, I can nearly always hear without looking, and "feel" through the seat of my pants as the drivetrain goes "loose".
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