Driving an '89 Cressida auto trans, cruising along in OD and encountering a slight hill or otherwise giving a slight amount of push on the accelerator, I'll notice what feels like a mild kickdown - I hear a definite change in engine/trans sound, the rpm's go up slightly, but it's not as big a change as going out of OD. I've checked by disengaging the OD and it's different, much more subtle than that.
Is there some kind of "intermediate" kickdown when in OD?
Besides allowing slippage when the vehicle is stopped, the torque converter provides torque multiplication when acelerating.
The transmission will downshift if you apply enough pressure to the accelerator. You'll notice it more if you use the cruise control since cc wait's longer before adjusting your speed than you do.
It's not intermediate. It really is just going back into plain-old third gear.
Mike is right - the torque converter is "locked up" to reduce slippage/improve mileage. a bit of resistance or slight acceleration causes it to unlock. It will (transmission) shift down with either more throttle pressure or increased resistance.
It's definitely not going out of OD into 3rd, it's far more subtle than that. I believe other responders have probably id'd it correctly as related to the torque converter.
Rather than trying to decide whose wild guess is correct or incorrect, it is very easy to tell for yourself.
Pushing the overdrive button will drop the transmission down to 3rd gear.
If you want to unlock the torque converter while at a steady cruise, tap the brake pedal just enough to make the brake lights come on. Having the brake lights come on will trick the transmission ECU into unlocking the torque converter. You should see about 100 to 200 RPM increase with the torque converter unlocked.
But it can't be that, the torque converter is a smooth process from 'no power out' to 'full power out'...there's no 'stages' involved,
If you keep increasing the TC input shaft speed then the output shaft speed (or power) will increase...this will continue until something breaks, the oil in there boils or the whole thing explodes.
I know what he means by this subtle rpm change, it certainly isn't the comparatively large rpm change that you get when you select 'OD off'...incidentally, what exactly are you doing when you select that OD switch?
Hey Doc, I believe Ray O has hit the nail on the head. It's pretty easy to determine what's going on. Hope you have a happy Thanksgiving. Bob
Ok Ray, so the 'overdrive' is merely 'another higher sped' gear in the transmission is it?...has nothing to do (directly) with the torque converter?
Ok, thanks...
Overdrive is just 4th gear. The sequence is 1 to 2; 2 to 3; TC lockup in
3rd; TC unlock and shift to 4th (A.K.A. overdrive), TC lockup in 4th.Since 4th gear is an overdrive gear, the transmission output shaft is turning more slowly than the engine so it takes a lot more torque to accelerate. To accomplish this, the TC unlocks to allow the TC to develop torque multiplication, kind of like twisting a rubber band, and if more torque is needed, then it downshifts to 3rd or 2nd, depending on vehicle speed and throttle position.
Right. If you go back to my original post I mentioned trying this and that it was comparatively very different than what I'm experiencing.
Hi Gord, Thanks for the christmas tree. It is a beauty as usual. Mayor Menino is going the politically correct route this year by calling it a holiday tree. Maybe you folks should think about stopping the tradition. Unlocking the torque converter was a feature of the Ultramatic transmission the 1950 Packard I once owned. The "bathtub".
Ron
Gord Beaman wrote:
I was home the day they erected the 'holiday tree' and they had an interesting survey on Channel 4. The only person calling it a 'holiday tree' was some yuppie white chick. Even the blacks and the foreigners were saying "Christmas Tree"!!!!
How is Mumbles these days?
We don't have yuppie white chicks in Boston. We have empowered young female type persons who are politically correct and use their empowerment to make this world safe from the demonic neo conservative ,beaver unfriendly type conservatives whether we like it or not. Minority rules.
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