Talk:Overdrive (mechanics)

Hi: I need to know when would it be apropiate to use the OD on or off, I live in Mexico City a very crowded town but I really dont know when to use the OD on or off, should I turn it off inside the city or what.

THANK YOU I'll WAITING FOR YOUR ANSWER.

EMAIL: rafaelg@rocketmail.com

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Rafael, 99% of driving should be done with the overdrive enabled.

Posted some edits, forgot to give references. http://www.ohiovw.com/files/touaregfiles/6speedautotranny.pdf http://bandwidthmarket.com/resources/patents/apps/2002/7/20020086761.html

http://www.sae.org/servlets/productDetail?PROD_TYP=PAPER&PROD_CD=2005-01-1020

http://techinfo.toyota.com/ Sorry, last two are pay sites, unfortunately that is where most of the good stuff, with lots of details is. 3sgte 16:35, 2 December 2005 (UTC)

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Coming at this as a clueless person, I didn't understand one thing after reading the article: How/why can overdrive be engaged without using the clutch? Good article otherwise.

I thought the same (my father had a Volvo 740 so equipped) the best answer I can offer is that the gear engages rather like the gears on an automatic box. So I can say why, but not how, sorry! Alastairward 11:22, 2 February 2007 (UTC)

When you start your car, many cars (such as the Nissan Altima) default to the state of the Overdrive being turned ON. You might find a button somewhere that takes it OFF, however. 198.177.27.23 (talk) 07:50, 19 October 2008 (UTC)

Bias Toward Automatic Transmission

When reading this artice, I notice that manual transmission was only mention once, with the remainder of the artice favoring OD in automatic transmission. I think this is Bias. --KB1KOI 15:32, 28 July 2006 (UTC)

Bias towards automatic transmissions

I do not believe there is a bias in this article, as in the manual transmission, the overdrive gear is treated like any other; while in the automatic transmission, it is usually electronic and switched on or off with the press of a button, but generally is not usually interfered with.

not bias

one of the reasons that this article may seem bias is becuase the automatic engine, switches to OD automatic-ly hence the name, where as manual you have to actually put it into OD

Rename Page?

I'm trying to find consensus for renaming "(mechanics)" pages, where "mechanics" refers to machinery, mechanisms, mechanical devices or mechanical engineering, rather than (e.g. classical) mechanics in physics and applied math. I would like to rename this page to "Overdrive (mechanism)" or "Overdrive (mechanical device)" or something similar. Any preferences or objections? Geometry guy 20:57, 21 February 2007 (UTC)

Drive train wear

I don't know a lot about mechanics, but the section in this article on drive train wear didn't make sense to me. Unless using an overdrive gear means you are going to drive faster than you have would otherwise, why would there be more wear on the drive train from using overdrive? i.e. isn't drive train speed fixed to vehicle speed? Interlope (talk) 20:20, 14 January 2008 (UTC)

I quess it has something to do with the speed and load of transmission. Lets say you drive an old car, equipped with four speed transmission, electric overdrive and a low rear end gear ratio for example. Remember, that the overdrive unit is basically an auxiliary two speed transmission, positioned right after the main transmission. If you run 100 km/h (~60mph) first without overdrive and then switch the overdrive on the main transmission speed (and the engine speed) is reduced while driving the same vehicle speed. Because power is relative to speed and torque (momentum), in order to keep the same vehicle speed (100 km/h or ~60mph) the main transmission must transmit the same power to the wheels with lower rotation speed. This means that the momentum affecting the transmission increases, and so increases the load and stress of its bearings and other mechanical parts. If the transmission is not build to withstand such increased load, it might break down. Or if the transmission speed while using overdrive is too slow for proper lubrication to take place, the transmission starts to wear at considerable rate and also becomes prone to fail.

Hopefully this was of assistance... —Preceding unsigned comment added by 80.223.93.188 (talk) 00:34, 7 January 2009 (UTC)

overdrive on a '98 Nissan Altima

I read the main article but remain confused as to the usefulness of the "overdrive" button on the stickshift of my '98 Nissan Altima.

The little overdrive button on the side is not the same thing as the big stickshift button on the top. The little one is located on the driver's side of the stickshift, about three or four inches down from the top. It's small, and measures about a quarter inch across, so you aren't likely to confuse it with the relatively larger stickshift button on the top, which measures about 2 by 3 inches. You change gears (like, going into reverse) if you push the big button down, and then pull the shiftstick back into the appropriate gear. But what on earth does the overdrive button do? I've heard gossip that it is useful when driving at high speeds.

In my case, the car is almost always in "overdrive" mode, but if you decide to press the overdrive button, it goes in a bit, so it is flush with the rest of the stickshift. Then a dashboard light comes on, and it says "O/D OFF" but what is even more interesting, the car's RPM will go up. This happened lately while I was driving in the 45 to 55 mph range.

Am I getting better miles per gallon if I am driving 50 mph on a relatively level road with the O/D button pushed in, so the overdrive is off? 198.177.27.23 (talk) 04:32, 16 October 2008 (UTC)

I have no knowledge of the'98 Nissan Altima and even less about the US version of it but overdrive works always the same way. Simply put: The overdrive works similarly to changeable differential. If you switch the overdrive off it is if you would cruise at smaller gears. It causes your engine rpm increase at the same vehicle speed which means your economy aka mpg drops but you gain more pulling power (torque to the wheels increases). I would assume that in this case overdrive should be switched off only when additional pulling power is required, for example when pulling loads or moving in difficult environment like climbing a steep hill... Hopefully this helped... —Preceding unsigned comment added by 80.223.93.188 (talk) 22:27, 4 December 2008 (UTC)

Cruise control versus Overdrive

At least on a '98 Nissan Altima, pushing the Overdrive Button in (so the O/D OFF light comes on), the rpm's go up. Does it make a difference if the car is being operated with the Cruise Control switch on? 198.177.27.16 (talk) 20:30, 16 October 2008 (UTC)

Cruise control is a separate system, a device with a sole purpose to hold the vehicles speed steady by adjusting engine rpm. It should have no effect to the overdrive: In other words driving with overdrive off your vehicle consumes more fuel wether you use cruise control or not. As stated before, in this case overdrive should be used unless extra pulling power is required... —Preceding unsigned comment added by 80.223.93.188 (talk) 23:56, 6 January 2009 (UTC)

Prevelance

I noticed something in the article that pretty much said overdrive is pretty much standard but I don't belive thats the case. The only modern cars I've seen with overdrive controls are nissans. Might this be a difference between UK/EU markets and other markets?(Morcus (talk) 03:27, 6 January 2011 (UTC))

I really need to write a decent lead for this article. "Overdrive" has four meanings.

The first is a high ratio (gerbox and final drive) such that the top speed of the car is less than it might be in a lower gear (although its fuel economy at the same speed will be better).

The second and third are mechanical means to achieve this. The older system was a separate "overdrive" gearbox attached to the output of the main gearbox, often electrically switched. Later systems (especially front wheel drive) merge this into an extra high ratio on the main gearbox.

This second form also gives the fourth meaning, again only applicable to rear-wheel drive, where the propeller shaft was turning more quickly than the engine.

As modern cars are now too fast to use their performance at all frequently, but fuel costs are astronomical, pretty much all cars are now "overdrive" by the 1st and 3rd meanings, although the 2nd and 4th have pretty much vanished. Andy Dingley (talk) 12:02, 6 January 2011 (UTC)

• I've rewritten the lead. Any clearer? Andy Dingley (talk) 14:35, 7 January 2011 (UTC)

That does make more sense, The way I read it when I posted that made it seem like it was refering solely to the old system where you had and extra bit of gearbox on the back, I'd assumed thats what this article was about for some reason rather than as you say when the final drive ratio is more than one.(Morcus (talk) 07:15, 8 January 2011 (UTC))

overdrive gear ratio

an overdriven ratio for cruising thus required a gearbox ratio even higher than this (1:1), i.e. the gearbox output shaft rotating faster than the original engine speed.

Isn't this backwards? An overdrive gear's ratio will be less than 1. Typically around 0.75.

20:19, 17 August 2011 (UTC)