Over-drive, what is it for?

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Old 17 Oct 2005, 02:04 pm   #1 (permalink)
Marc Raizman
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Default Over-drive, what is it for?

Sorry fellows but I have never owned a car with an over-drive. Consequently,
I don't know what it is supposed to do in my '99 Camry. When do you press
the button that brings the O/D on? Considering the current cost of fuel, is
it more economic driving with O/D on or not? Thanks and best. MR


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Old 17 Oct 2005, 03:02 pm   #2 (permalink)
DSPL
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Default Re: Over-drive, what is it for?

Definition: Any gearset in which the output shaft turns faster than the
input shaft. Overdrive gears are used in most modern transmissions because
they reduce engine rpm and improve fuel economy. Occasionally, a separate
gearbox with an overdrive gearset is coupled to a conventional transmission.

In short, it's a fifth gear for your 4 gear automatic transmission.


"Marc Raizman" <mraizman@intergate.com> wrote in message
news:11l7tddoq8fqlce@corp.supernews.com...
> Sorry fellows but I have never owned a car with an over-drive.
> Consequently, I don't know what it is supposed to do in my '99 Camry. When
> do you press the button that brings the O/D on? Considering the current
> cost of fuel, is it more economic driving with O/D on or not? Thanks and
> best. MR
>



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Old 17 Oct 2005, 03:26 pm   #3 (permalink)
badgolferman
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Default Re: Over-drive, what is it for?

Marc Raizman, 10/17/2005, 3:04:21 PM,
<11l7tddoq8fqlce@corp.supernews.com> wrote:

> When do you press the button that brings the O/D on?


Others will refute this but your owner's manual will suggest you leave
it on.

--
"The harder I work, the luckier I get." -- Gary Player
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Old 17 Oct 2005, 04:44 pm   #4 (permalink)
ag
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Default Re: Over-drive, what is it for?


On the 99 Camry 4 cylinder the default is ON.

When you press the button (engage it) you actually turn overdrive off.

In heavy traffic and rain and snow I always leave the overdrive off for
seemingly better engine performance.

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Old 17 Oct 2005, 05:29 pm   #5 (permalink)
DSPL
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Default Re: Over-drive, what is it for?

Overdrive only works at higher (not necessarily fast) speeds (4th gear
speeds). It will not engage during acceleration but rather at a constant
cruising speed. Test it you'll see... On the highway at 100km/h, with o/d
on, set the cruise control. Once set, turn off overdrive. Your car will
down shift (o/d to 4th), engine will turn faster (rpm) but you wont go any
faster. All it does in the end is save gas. 87-91 camrys (I don't know
about this feature in later models) have a power/normal(economy) button as
well as the O/D button. When set to power, the transmission shifts at a
higher rpm thus giving the car better acceleration (faster). High rpm =
high gas consumption





"ag" <ottawaon@gmail.com> wrote in message
news:1129585474.869292.100270@g43g2000cwa.googlegr oups.com...
>
> On the 99 Camry 4 cylinder the default is ON.
>
> When you press the button (engage it) you actually turn overdrive off.
>
> In heavy traffic and rain and snow I always leave the overdrive off for
> seemingly better engine performance.
>



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Old 17 Oct 2005, 07:23 pm   #6 (permalink)
Merritt Mullen
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Default Re: Over-drive, what is it for?

In article <11l7tddoq8fqlce@corp.supernews.com>,
"Marc Raizman" <mraizman@intergate.com> wrote:

> Sorry fellows but I have never owned a car with an over-drive. Consequently,
> I don't know what it is supposed to do in my '99 Camry. When do you press
> the button that brings the O/D on? Considering the current cost of fuel, is
> it more economic driving with O/D on or not? Thanks and best. MR


"Overdrive" is simply your highest gear (normally the forth gear in an
automatic transmission: Low, Second, Drive, Overdrive). Your car will
automatically shift into overdrive when your speed and acceleration is
appropriate (cruising at moderate to high speeds). When more power is
demanded, such as for passing, your transmission will automatically shift
to a lower gear. You should normally leave overdrive on, except when you
want to prevent your car from shifting to the highest gear (maintaining
speed while climbing a steep hill is the most likely occasion). Your car
will automatically shift into overdrive when your speed and acceleration
is appropriate (cruising at moderate to high speeds).

Overdrive "ON" is the normal position, if you push the button to turn
overdrive "OFF", you will see a red or yellow light on the gear indicator
that says something like "O/D OFF" to remind you to turn it back on.

If you drive with O/D off, you will never shift into the highest gear, and
therefore your engine will be running faster than necessary and burning
more fuel. These days, you surely don't want to do that.

Merritt
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Old 17 Oct 2005, 07:42 pm   #7 (permalink)
Hachiroku
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Default Re: Over-drive, what is it for?

On Mon, 17 Oct 2005 13:04:21 -0600, Marc Raizman wrote:

> Sorry fellows but I have never owned a car with an over-drive. Consequently,
> I don't know what it is supposed to do in my '99 Camry. When do you press
> the button that brings the O/D on? Considering the current cost of fuel, is
> it more economic driving with O/D on or not? Thanks and best. MR



My experience is mostly with 5 speeds manuals, but in practice I find with
my Mom's Camry I get better mileage around town with the OD OFF. On the
highway it's better on.
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Old 18 Oct 2005, 08:51 am   #8 (permalink)
m Ransley
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Default Re: Over-drive, what is it for?

Overdrive lowers engine rpm, it is a higher gear. A slower running
motor- rpm, lasts longer, that is why diesels last. A motor that turns
half the rpm say 1800vs 3600 lasts 4 times as long. I leave mine on.
Overdrive will not be active till the motor reaces 110-120f. It also
improves highway mileage, esentaily it is just a 4th gear, but one that
will activate at even low engine speeds. Leave it on, the transmission
automaticly does whatever you need. I imagine for moutains or heavy
loads you may want it off, but normaly it is left on.

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Old 18 Oct 2005, 10:46 am   #9 (permalink)
Hachiroku
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Default Re: Over-drive, what is it for?

On Tue, 18 Oct 2005 08:51:05 -0500, m Ransley wrote:

> Overdrive lowers engine rpm, it is a higher gear. A slower running
> motor- rpm, lasts longer, that is why diesels last. A motor that turns
> half the rpm say 1800vs 3600 lasts 4 times as long. I leave mine on.
> Overdrive will not be active till the motor reaces 110-120f. It also
> improves highway mileage, esentaily it is just a 4th gear, but one that
> will activate at even low engine speeds. Leave it on, the transmission
> automaticly does whatever you need. I imagine for moutains or heavy
> loads you may want it off, but normaly it is left on.


The one in my Tercel kicked in at 35MPH! The only problem was, when you
turned it OFF, you were stuck in Third gear. It would only go into 4th
with the OD on, and then lock-up came way too early.

In the '86 Camry, we get better mileage with it OFF for general
around-town driving. It shift into OD about 37 MPH, not good for around
town.

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Old 21 Oct 2005, 11:39 am   #10 (permalink)
Daniel
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Default Re: Over-drive, what is it for?

Simplest way to think of it is that you have an automatic transmission,
and it will automatically select the right gears for you. Just put the
car in Drive and go. Do not turn overdrive off.
Your four speed transmission is acutally like a five speed.
Automatic Transaxles, 1st, 2nd, 3rd, 4 th. Trans, Gear, Gear, Gear,
Gear. Model,
Ratio, Ratio, Ratio, Ratio. A140E, 2.810, 1.549, 1.000, 0.706
See the last gear ratio is less than "one" so technically it is
"overdriven".
The reason I say it operates like a 5 speed is that you also have
torque converter lock up which links the flywheel to the transmission
input shaft like a manual transmission with the clutch engaged.
If you're climbing a hill in overdrive and observe the tachometer,
first the torque converter lockup releases and the tach needle moves
slightly, (almost like going from fifth gear to fourth), the if the
hill steepens or you press the gas pedal further, at speeds under apx.
95 mph., the transmission will down shift into third gear.

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