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Burnt Transmission Fluid?


wwest

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Lots of buzz is going around about acceleration hesitation on all Toyota/Lexus FWD, or front drive biased AWD vehicles. The rumor is that the RX has been fixed.

On another forum someone posted that they noticed that their Sienna engine RPM rises about 500 to 1000 RPM when applying the brakes while coasting downhill.

That got me to thinking out loud....

COPY

Probably part of the hesitation issue/problem.

With the Prius you can chose to use the regeneration system to simulate engine lagging torque or you can chose actual engine lagging torque. In the latter case they tell you that fuel economy will suffer.

Suppose, say back in 01, Toyota learned from the Prius experience that if you put the transmission in neutral during any type of coastdown, the fuel economy is increased by 2 to 3%

Note, the EPA would be involved....

My 01 AWD RX300 certain seems to have this feature. When I lift my foot from the pedal at highway speeds it seems/feels as if the tranny shifts into neutral. The other time I notice this is just before coming to a stop, at just about the time I would release the clutch with a manual transmission the vehicle suddenly feels as if someone bumped me from behind lightly.

I'll have to go out and check but I wouldn't be surprised that during highway coastdown if I apply the brakes slightly the transmission would shift back into gear to add the engine lagging torque back into the braking equation.

Just as flyingfox described above.

Now, here I am, sitting stopped at a traffic light, inadvertantly with the transmission not in 1st gear, and I decide to dig-out!

Really rough on those transmission clutches and bands, going from neutral or second into first while the engine is climbing in RPMs. No e-throttle here!

Strange. My RX doesn't require any transmission fluid service, EVER. At least according to the owners manual. I have asked Lexus (customer_satisfaction_inquiries@lexus.com) why, at only 38k miles, with the extra towing cooling package, and NO hitch, my transmission fluid is looking burned and has a slight burned odor.

Their written response is that I should take it in to the dealer.

Remember that these vehicles were shipped with a specific EPA standard MPG rating. Haven't I seen somewhere that the 05 RX has a lower MPG rating than the 04?

And the RX no longer has the hesitation problem...!!

So how would Toyota keep the higher MPG and still prevent those bands and clutches from wearing out too soon.

why not use an e-throttle to delay engine torque onset while we shift the tranny into the proper gear??

No burned clutches or bands and no notification to the EPA, or the public, that the MPG was miscalculated.

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I'll have to go out and check but I wouldn't be surprised that during highway coastdown if I apply the brakes slightly the transmission would shift back into gear to add the engine lagging torque back into the braking equation.

If you apply the brake and you are in lock-up, which you probably will be going along a highway, the gearbox will come out of lock-up.

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In lock-up the engine will turn, is forced to turn, at the rate of the transmission input shaft. Out of lock-up the transmission input shaft, during coastdown, is "driving" the torque converter. In that case the engine RPM would drop, not rise.

Out of lock-up:

When the engine is "driving" there is always a loss of RPM through the torque converter. When the engine is lagging, coastdown, reversing the "drive" path, the engine will always turn slower than the transmission input shaft.

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