What is the little button on the shifter thing that says overdrive? I have read some things about it relating to rpms and gas mileage, but what exactly does it do, and what are the advantages/disadvantages of having it engaged?

 

over drive is just a gear in the tranny like 1, 2, and 3. It is a long gear that helps fuel economy on the highway because it allows you to cruise at a lower rpm and maintain high speeds. The only draw back of overdrive is that it is gear so long that it is weak on power.

Turning it off just allows you to say in a better power band at higher speeds.

 

From what my dealer told me, you should always have the overdrive engaged on the car.

Anywone have any thoughts on that? good or bad?

I have had it engaged the whole time I have owned the car and so i don't know the difference without it. Things have been great so far.

 

I have no idea why anyone would tell you that . Not having it engaged will just not let you shift into overdrive, that is it.

 

basically overdrive is 4th gear in our tranny. i keep it off unless i go on the high way

 

So is it bad to have it engaged all the time? Or does it not matter either way?

Hmmmmmm.....

 

So does leaving the overdrive off in the city helps with gas mileage?
I noticed when the overdrive is off, my rpm are lower in the city and the highway.
I always have the overdrive on.

 

No. But it might prevent frequent shifting between 3rd and 4th(overdrive)

Rpm's can't be lower if the overdrive is off, because you're preventing the tranny from using 4th gear, which basically is the overdrive. So rpm's will be higher with OD off (that means the light is on)...

 

If you had a 5 speed manual you would use all gears, right? Now, the AT has 4 gears. The 4th gear has a fancy name:Overdrive. Regardless of names, we should use all gears! Maybe we could name 1st. 2nd. and 3rd. also? Start in underdrive.... continue in intermediate1-drive followed by intermediate2-drive and overdrive.......... Just makes it hard!

So to all of you wondering what overdrive is: It's just 4th gear!!!! Use it!!

 

I think the problem occurs when travelling low speeds, if you have overdrive on, the tranny tends to upshift to lower rpm's.

If overdrive is off, it doesn't shift as much at all. I think even sometimes it shifts from say gear 2 to 4 if overdrive is on.

It's kinda a wierd thing to feel sometimes it feels like you have no power on the pedal, and when you floor it, it has to shift all the way back. Well that's been my experience with it anyway. Sometimes I have to turn overdrive off just to get on highways as you really have to floor it otherwise to shift gears to make it into traffic...

 

Agree... have that feeling too sometimes. Does the US models have the sport/snow switch for the tranny? Because when I set mine to sport, it keeps the gears longer and also downshifts must faster without flooring the pedal...

 

Damn I love my 5 speed manual

Someone said that you should allways overdrive cause you allso use all gears in a manual?? What kind of c r a p is that??? I have a 5 speed manual, and if I want to race someone on the highway I use only 3d and sometimes a part of 4th gear. I pull to 170 kp/h in 3d, and most of the times the rival has enough of it by the time I'm at 170, happens kind of fast with a 3 litre 5 spd manual sometimes I shift up to 4th and rev it through, by the time I'm at 200 kp/h I don't see them anymore, and if the other guy wins I call it a day and give him a big thumb upwards for winning. No need to endanger my life or that of anyone else.

And I havent even used 5th gear, so wtf are you talkin about that you MUST use it... in my opinion you should take it easy on smoking pod when you start saying crap like that .

If I'm cruising then I use 5th to stay in low RPM, reduce engine sound and improve fuel economy. But you definatly don't need it. Even the auto tranny should be able to do 80 mph / 120 kph without overdrive engaged. So if you use it or not is all up to how you want to drive, in low or high rpm, and if your willing to feed the car more gasoline then avarage.

Am I wrong?

 

doesen help on gas milage but it does let you increase speed faster and yes it doesent shift as frequently so rpms go higher so you get max hp and tourque of your engine.

 

overdrive is just the next gear. i will hvae it on when i'm in the highway (generally at 50mph or higher). the gear shifts, the rpms go lower, and my fuel economy goes up.

if i'm climbing a hill or need to accelerate, i turn overdrive on to have the gear shift down, rpm rev, and more power to the wheels so i move faster.

 

which yields the best fuel economy on/off?
which yields best accelleration on/off?
Which is better for city driving on/off?

i think these 3 questions will answer everyones questions about overdrive. Overdrive is 4th gear. this equation helps:

Overdrive = 4th Gear

 

From my experiences in my 96 Maxima:
Better fuel economy: on
Better acceleration: off
Better in the city: off

I've found that acceleration from a roll is better (for instance, when you're slowing down at a red that suddenly turns green) with OD off as the highest gear the car will be in is 3rd. I measured fuel economy with OD on and off and found having OD off yields slightly better mpg. However, with OD off, you get a smoother feeling ride due to the car shifting less frequently and when it does, has one less gear to hunt for.

~THT

 

Just try it out for yourself, it won't hurt your car, test it while cruising and test both options when smashing tha gass, you will feel the difference... believe me, use whatever setting you find suitable for your needs, thats why there is a buttom, if it would damage the car they wouldn't put a button for it there, man, it's an infiniti / nissan

 

I know not everybody is car savy........but come on, are we really going to have a whole thread on what overdrive is? I don't even think you should be driving a car if you don't know what it is.

 

ROFLMAO

 

I like monkeys and candybars!

 

I like manual gearboxes

 

I agree 100%.

 

which yields the best fuel economy on/off?
on highway, on. city, off.

which yields best accelleration on/off?
off

Which is better for city driving on/off?
off

and i agree with mike's comment about overdrive. just use and you'll understand how it works. esp when you think about it as a 4th gear of sorts.

if you're driving in the city, it's best not to have it on because you're gonna accelerate slower... less power to the wheels. but once you're on the highway and you're close to your desired speed, turn it on, you'll yield better fuel economy.

that's all folks! :wabbit:

 

I swear to god my AT feels like it has 5 gears, but only when OD is on, if its off it is clearly the 3, but when you turn it on, you can definately feel the car either shift a gear, or shift something, because it shifts twice, its very suttle, but it is definately there, i had to prove it to my friend... am i crazy?

 

No... that is just your torque converter doing that smaller little shift. I know what you mean though... it almost makes the car feel like the transmission has mini gears between the main gears. Your transmission only has four gears though (although if you think about it the torque converter does act like a fifth gear in a round about way).

 

ok my 99 max, automatic.. drives kinda slow with overdrive on.. it shifts good and everything but I just can't get it to go FAST from the get go. Even if I punch it its like not as responsive as other cars i'm used to driving... any ideas as to why..are all 99 max's auto like that..??

if i drive with OD off, then it drives like how I want it to drive. really FAST.


is it bad for your tranny to click OD off while going like 75 mph?

 

That's the torque converter lockup. Usually the automatic transmission has a fluid coupling to mate engine and transmission. Once the car detects certain parameters (speed, rpm, etc) it will mechanically engage engine and transmission so no power is lost through slippage in the fluid link.


Are you familiar with the workings of a manual transmission clutch and how it works, and the torque converter in an automatic (which takes the place of a clutch)?

Here's the simplified explanation.

Imagine you have two of those "box" style fans facing one another. One is plugged in, and the other is not. There are no "safety grates" on these fans, just the frame and the spinning bits.

If you turn the powered fan on, it will create wind. The wind created from that fan will cause the second set of blades in the unpowered fan to turn.

This is essentially the principle behind the torque converter in a car, except instead of air as the power transfer medium, a special oil is used (Automatic transmission fluid.)

You will notice that if you tried to slow or stop the blades in the unpowered fan by touching the blades with your hand or a pencil, the blades will indeed stop, however the powered fan will still spin under its own power.

The example with your hand stopping the unpowered fan is similar to coming to a stop with an automatic transmission - the engine can idle while the wheels are stopped. (if you tried to stop a car with a manual transmission in gear, the engine would stall)

The "soft coupling" of the two fan blade sets allows for some flexibility between the power and driven sides. However, this flexibility has a cost: efficiency. It's safe to assume that if the powered fan is turning at 500 RPM, the driven fan may only be going 400 or even less. In an automotive application, this translates into lost power and MPG. If only there were a way to eliminate this waste of energy.

The answer to that problem? The Torque Converter Lockup

Let's assume the engine "knows" when the car will not need to have that flexibility for a while -- say whenever the vehicle is moving 35mph or faster.

Imagine the two fans being pushed together in such a way that the blades are sandwiched together, providing a direct link for power transfer.

This is how the torque converter lockup works.

The mechanics out there will have a zillion things to point out that I missed, however this was an intentionally simplified example, not an engineering thesis on the complete innerworkings of an automatic transmission.

 

So far you all fail Automotive 101 class. Read this link(below).

http://en.wikipedia.org/wiki/Overdrive_%28mechanics%29