Basic but important question on Overdrive (OD) (2 Viewers)

[AtinLango]

In an automatic transmission, I know that OD ON allows shifting to the highest gear. OD OFF disallows shifting to the highest gear. In my case (Landcruiser 100 Diesel Automatic Transmission, Year 2002), the highest gear is number 4.

Now, my question is: does OD OFF increase the power (or torque??) in addition to disallowing the highest gear? Let me illustrate my question more.

Assuming I am parked at the bottom of a very steep hill. Then I start the car to climb the hill from rest. Does it help to put OD OFF and start climbing the hill? Will it give more power to climb the hill?

Sorry, the question may look trivial, but I am sure it will help many others too.

 

[magikaram]

OD gear is #4, when starting from a stop - you'll start in 1st, then 2nd, then 3rd, and lastly 4th.
The transmission will select the gear based on your throttle position and the speed you're going, so if you're going up a hill and push more onto the pedal, you'll notice a downshift from whichever gear you're in to the next one.

As for switching off overdrive, you don't need to switch it off unless you're doing "abnormal" driving, like pulling a trailer - you often do not want to use O/D while pulling a heavy trailer. It all varies when you would want to use the 'off' switch. I'd consider instead if you need more torque going up a really steep hill, to use 2nd gear instead of disabling over-drive, but that's only if 3rd isn't even pushing you up the hill.

 

[Broski]

Simply put, NO

 

[nissanh]

Think of a 5-manual transmission. The OD is like the 5th gear, when you go uphill you'll never get into the 5th similarly OD on or off does not matter when climbing a steep hill. On highways; OD should be ON, but when pulling a trailer as magikaram said above, turn off the OD.

 

[AtinLango]

I agree with all the above answers. That is what I have known all my driving life. But it is interesting to hear so many people I meet (including mechanics) argue that you should always put OD OFF when climbing a steep hill, no matter the vehicle speed. One mechanic even blamed me for climbing a very minor hill without setting OD OFF. That I was damaging the transmission.

Because I dont drive under abnormal conditions, I do not set OD OFF, except when I just want t test that it is working. Same with DIFF Lock.

 

[Mike NXP]

I agree with all the above answers. That is what I have known all my driving life. But it is interesting to hear so many people I meet (including mechanics) argue that you should always put OD OFF when climbing a steep hill, no matter the vehicle speed. One mechanic even blamed me for climbing a very minor hill without setting OD OFF. That I was damaging the transmission.

Because I dont drive under abnormal conditions, I do not set OD OFF, except when I just want t test that it is working. Same with DIFF Lock.

From a dead stop it doesn't matter......but if you're driving around windy twisting roads with elevation changes, you can keep OD off to avoid so many gear changes and to hold more power up hills. I believe the owners manual gives a certain speed range they suggest for turning OD off in these conditions. It also helps to control your downhill decent in certain situations.