Will it hurt to drive my 2001 4x4 SR5 2.7L up and down these WV mountains without the overdrive?
I can feel it shift without it on the upgrades bot not on the flats. It feels like I'm always in third gear but it does seem to be much easier on the truck overall to leave the overdrive off while driving the mountains. Thanks for your openions and knowledge. Mike

It will actually help your transmission to have overdrive off...

The excessive heat generated in an automatic transmission comes from the torque converter working hard in torque multiply mode.. it is better to down shift so the torque converter is not trying to do all the work..

When you switch overdrive off, not only does it lock out going into forth gear, but the transmission ECU is much more aggressive in keeping the torque converter locked as much as possible to minimize heat build up... a good mode for mountain driving to keep transmission temps down..

Toyota also recommends turning overdrive off if towing a heavy load for the same reason..

The effective gear ratios of 4th gear, unlocked torque converter in heavy torque multiply mode and and 3rd gear, torque converter locked are about the same, but the transmission is producing a lot less heat in the latter mode..

You might want to read this about lockup torque converters....

<small>[ June 09, 2003, 11:04 PM: Message edited by: Dandeman ]</small>

I am turning overdrive off and on all the time when I am in WV (make a trip every year to Tucker Co) It depends on how steep the grade is.

Dandeman, Thanks for the great info and the great site.
It seemed to me that it was not shifting without the overdrive and that's what concerned me. It would shift on the steep upgrades but not on the down side or if i hit a flat area for a mile or two.Is that normal? Mike

Tacorunner, Thanks for the imput on this subject. I live in Clay County (Central WV) and it's the norm of the day around here to go from 900 feet above sea level to 2200 in a hurry.
It seems like you climb forever then it flattens out for about a mile then straight back down. For me to go to town i climbed over three of these just to get there <img border="0" title="" alt="[Smile]" src="images/icons/smile.gif" />
With this auto transmission it handles it real well but it does it alot easier without the over drive on. I'm not sure how much difference it would make on gas milage and really not to concerned about that.
It's hard to get used to the idea that it's not shifting unless I'm climbing a really steep grade. It just feels like something has to give or i need to shift it,lol. Mike

Tacorunner, Thanks for the imput on this subject. I live in Clay County (Central WV) and it's the norm of the day around here to go from 900 feet above sea level to 2200 in a hurry.
It seems like you climb forever then it flattens out for about a mile then straight back down. For me to go to town i climbed over three of these just to get there <img border="0" title="" alt="[Smile]" src="images/icons/smile.gif" />
With this auto transmission it handles it real well but it does it alot easier without the over drive on. I'm not sure how much difference it would make on gas milage and really not to concerned about that.
It's hard to get used to the idea that it's not shifting unless I'm climbing a really steep grade. It just feels like something has to give or i need to shift it,lol. Thanks again guys for all the help, Mike

</font><blockquote><font size="1" face="Verdana, Tahoma, Arial, Helv, Helvetica, Sans">quote:</font><hr /><font size="2" face="Verdana, Tahoma, Arial, Helv, Helvetica, Sans">Originally posted by Beartracker:
<strong>Dandeman, Thanks for the great info and the great site.
It seemed to me that it was not shifting without the overdrive and that's what concerned me. It would shift on the steep upgrades but not on the down side or if i hit a flat area for a mile or two.Is that normal? Mike</strong></font><hr /></blockquote><font size="2" face="Verdana, Tahoma, Arial, Helv, Helvetica, Sans">I think sensation that it's not shifting a lot when out of overdrive is two things...

1)As mentioned earlier, to minimize heat build up, the ECU is keeping the torque converter locked as much as possible.. It will let the engine pull quite hard in 3rd locked, which almost feels like the sensation of having a manual transmission, With it in 4th you can feel the torque converter locking and unlocking fairly regularly, which feels like a gearshift.. which in effect it is, but has it's heat producing downside in sustained use..

2) and since 4th is locked out, the only "shifts" available are to downshift to 2nd or unlock the torque converter in 3rd.. To get it to do either you got to hammer the throttle pretty hard or pulling a steep and slow hill..

If you got a long straight uphill road grade close by it's a good place to experiment a little to get a better feel for what the transmission is doing..

When I first got my 4Runner, I did some playing on a nearby hill.. e.g. while going up the hill with the switch in overdrive postion, let the transmission get into in 4th gear and locked TC, then very slowly push the accelerator down while also watching the tachometer... first you'll feel the torque converter unlock and (I think, been a while since I did this) about a 600 rpm engine increase... very slowly keep pushing the accelerator down keep an eye on the tach and speedometer so you know the readings just before it downshifts into third...

In doing the above you are pushing the torque converter into it's max torque multiply mode.. some folks say it's "slipping" and in a way it is, but what is really happening is the fluid flow path inside the TC is changing to in effect approach about a 1.8:1 "gear" ratio through the use of the hydraulic fluid.

Now do the same hill again in 3rd, TC locked and match the speed you were doing above just before it downshifted, and you'll see the engine rpms will be near identical in 3rd, locked TC as when you were running in 4th, TC unlocked.. so you got about the same effective gear ratio, but it's a lot easier on your transmission in terms of heat build up to be in 3rd..

As you press the accelerator harder while in 3rd, you'll see that the transmission very reluctant to let the converter unlock in 3rd as it tries to keep it in it's least heat producing mode for as long as possible...

And of course on the down slopes, you get more engine braking effect with the transmission staying in 3rd...

Lastly haven't mentioned the ECT being in power or normal mode, but this certainly will affect when and how much throttle you got to have on the make it down shift..

For most of my life I've been a 5 speed guy, but reluctantly bought a Toyota with an automatic. I since been impressed with the flexibility and controls like the ECT and overdrive control that you can still fiddle with for various road conditions...

<small>[ June 10, 2003, 10:22 AM: Message edited by: Dandeman ]</small>

Dandeman, thanks for all the help and the great info you have shared. I will play with it a little and see how it acts. Thanks again, Mike