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Hi All.

Probably a stupid question, but what exactly does the over drive do and when and in what conditions should i be using it? Also...when you push the button, the light on the dash says "OD Off" ?? does that mean if the light on the dash is not on that over drive is on? Obviously i can tell that when i push the button and the light says OD off, the revs pic up but what else does it help with?

Cheers and sorry if im asking an obvious question!

Cheers
Boley :confused:
 

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Hey
Overdrive as the name suggests is like having one or multiple more wheel rotations at a specific engine speed. In simple language it helps the engine run at lower rpm(lower revolutions per minute) and helps you save the fuel.
Good to be used at flat and downhill runs under no load.

In cars, what is overdrive for? What does it do your car, fuel consumption? - Yahoo! Answers
http://en.wikipedia.org/wiki/Overdrive_(mechanics)http://wiki.answers.com/Q/What_are_the_uses_of_overdrive_and_when_should_it_be_used
http://wiki.answers.com/Q/What_are_the_uses_of_overdrive_and_when_should_it_be_used
 

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Hi B18C.
Im sure your right and my understanding is flawed however I have always believed that overdrive has a low gear ratio and hence spins much faster. because of this you should avoid overworking it, load, hills ect ??
I always believed that idealy OD should be used mostly on flat and downhill runs under no load.
Feel free to correct me.
Thanks.
 

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Hi B18C.
Im sure your right and my understanding is lawed however I have always believed that overdrive has a low gear ratio and hence spins much faster. because of this you should avoid overworking it, load, hills ect ??
I always believed OD should be used mostly on flat and downhill runs under no load.
Feel free to correct me.
Thanks.
No need to correct you when your already correct, my mistake.
 

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Overdrive - Wikiautos
"Overdrive is the final drive gear in a transmission which provides an extra-high gear ratio in exchange for a loss in torque. The extra-high gear ratio allows the engine to run at a lower speed, and thereby saves fuel and wear on the engine components. The overdrive also allows for smoother and quieter operation while at highway speeds. When an automaker refers to overdrive, they are referring to the highest gear in the transmission as long as it has a gear ratio greater than 1:1. The output of the transmission is spinning faster than the input, hence the term "over" drive."
 

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Something that has been bugging me also:

In the Patrol's 4 speed auto is overdrive fourth gear? i.e if you have O/D off, the car won't change to fourth gear?

Or is overdrive like another gear that affects all four gears (i.e. overdrive on affects the gear ratio on all gears, similar to high/low range in the transfer case?
 

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Grenade Master
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Or is overdrive like another gear that affects all four gears (i.e. overdrive on affects the gear ratio on all gears, similar to high/low range in the transfer case?
Not in Patrol for sure but a "splitter" is usually other way around it gives additional reduction in low split and direct in high split this is mostly on trucks and usually referred to as "half gears" I personally think this is what is missing in my Trol for sure as the gearing ratio can be more finely matched to suit that narrow torque band of the asthmatic 3.0L. Dreaming ....
 

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Something that has been bugging me also:

In the Patrol's 4 speed auto is overdrive fourth gear? Yes the overdrive is 4th gear & only when in OD mode which is greater than 1:1.i.e if you have O/D off, the car won't change to fourth gear? No, the auto will change to 4th (1:1)

Or is overdrive like another gear that affects all four gears (i.e. overdrive on affects the gear ratio on all gears, similar to high/low range in the transfer case?
OD only effects the final drive gear, not all gears. My shift pattern is different with the OD button in the off position.
 

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OD only effects the final drive gear, not all gears. My shift pattern is different with the OD button in the off position.
A while back i thought OD was working on each gear as even in for instance in 2nd, i could feel a change when switching the OD on or off. (maybe the torque convertor locking/unlocking). But when you check the specs OD is just 4th gear. So that must be the answer Helsms'y, the OD switch must change the shift pattern.

Ta

Grogey
 

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Not in Patrol for sure but a "splitter" is usually other way around it gives additional reduction in low split and direct in high split this is mostly on trucks and usually referred to as "half gears" I personally think this is what is missing in my Trol for sure as the gearing ratio can be more finely matched to suit that narrow torque band of the asthmatic 3.0L. Dreaming ....
I think the nissan engineers rely heavily on the torque convertor to split the gears. But i understand what you're saying. OD is very tall for the stock engine and I leave off when below 80kph.

When i get my engine mods complete (dawes, 3" exhaust and eventually a chip) I'm hoping taller, wider torque will improve the shift feel between ratios and enable the auto box to hold the gears longer for a smoother drive. For those of you who have done this; am i also Dreaming?

The Auto is a reliable unit and i will admit to preferring it to the manual.

Cheers

Grogey
 

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When i get my engine mods complete (dawes, 3" exhaust and eventually a chip) I'm hoping taller, wider torque will improve the shift feel between ratios and enable the auto box to hold the gears longer for a smoother drive. For those of you who have done this; am i also Dreaming?

The Auto is a reliable unit and i will admit to preferring it to the manual.

Cheers

Grogey
An improvement in OD is evident with the exhaust up grade & chip, less hunting with the Auto. Shift "feel" is no different in mine, it just upshifts quicker if that makes sense.
 

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Any gear that has a higher than 1:1 ratio is technically an overdrive. Electrically actuated overdrive units were commonaly fitted to cars in the 60's and 70's and were a separate unit that attached to the back of the manual transmission. They usually worked in 2 or 3 gears of a 4 speed box and were just a substitute for a 5 speed transmission. Beats me why Nissan call 4th gear of a 4 speed auto overdrive, technically it is but I think it's confusing. A lot of modern 6 speed transmissions have 2 or more overdriven gears.
 

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From my understanding a 4 speed auto with overdrive has the first 3 gears then it goes into overdrive which drops the revs a couple of hundred then it will go into lockup at a given speed say 90kmph depending on load and throttle position resulting in a further reduction of revs. The box will go into overdrive at say anything from 60km/ph
If you are going up an incline and you are in lockup it will drop out to overdrive then if you need more power it will drop back to 3rd.
My Nissan done this prior to it being a manual, Our previous VN commodore was the same with the turbo700 box and our Avalon we have does the same thing.
So really you have 5 changes of gear in theory.
 

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ZD30 Out - L77 In!
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Overdrive is simply as its name suggests, “overdriven” where the output shaft turns faster than the input shaft. It allows the use of lower speed diff ratios and the ability to have reasonably good high vehicle speeds without using as many revs.

In our case as with most 4 speed transmissions, 4th is overdriven and uses a clutch in the converter to reduce heat and converter slippage as well as limiting lost power through the converter.

Overdrive should only be used above 80km/h for several reasons. The transmission will run very hot below 80 in 4th because the converter clutch won’t engage and more importantly, there is no engine braking in 4th because it incorporates an over-run clutch. Anyone using O/D in the city at low speeds should expect to go through brake pads quicker.

The Jatco RE4R03A transmission used in the Patrol is a strong and proven transmission that’s been around since the 80’s and is generally good for around 200K in standard form. There are a few mods which can increase its life well beyond that and make it much better to drive.
 

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As for the hunting gears Starion on the forum here helped me (with the help of his son) install the torque converter lock, its great, stops the converter unlocking when u back off for a second and just keeps it locked in. Thanks again Starion.

As for asthmatic, they certainly are when towing, but overall i reckon theyre great.
 
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