Automatic Transmission (Not quite fit in but help me out)

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MicroXcorp
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Automatic Transmission (Not quite fit in but help me out)

Post by MicroXcorp » Mon Jul 05, 2004 10:46 pm

I started out with manual transmission so i'm not familiar with automatic transmission, I recently had my clutch change and I had to drive automatic. Its pretty much like manual except you don't have to shift while you're driving but there is one thing I don't understand that it has D with a circle and a stand alone D, so I asked my dad, he said the D with a circle is overdrive and the D alone is drive, but he couldn't tell the difference between them two except one consumes more gas than the other.

1. Whats the difference between overdrive and drive, and which one produces more power?

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Post by silent » Mon Jul 05, 2004 11:09 pm

thats what my dad told me too. That you save gas. In my parents car it only has a D but the dealer said that it is overdrive. Not sure if he is telling the truth.

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Post by IMBoring25 » Mon Jul 05, 2004 11:24 pm

An automatic transmission is just like a manual transmission, in that it changes how fast the engine turns at a given vehicle speed to give (in simplified form) either more power or more fuel economy, as appropriate.

Modern transmissions generally have an Overdrive top gear, in which the engine spins fewer times than the parts from the back of the transmission to the differential. The engine still spins more than the wheels because the differential has a reduction ratio in it that generally overpowers the overdrive ratio. However, all that really matters for this discussion is that overdrive is generally the top gear.

When you select Overdrive in an automatic, the car will use all the gears as it sees fit. There are times, however, when you want to lock out the top gear, which is what Drive does.

The times you might want to lock out the top gear include when you're driving along and the car is jumping back and forth between the top two gears (which causes a lot of stress to the transmission) and when descending a long, steep hill so that the engine braking helps to prevent brake overheating and fade.

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Post by IMBoring25 » Tue Jul 06, 2004 12:23 am

silent, what kind of car is your parents'? It certainly should be an overdrive if it's more recent than mid-'80's, and probably would be for several years earlier.

Some vehicles use a "D" position for both OD and D and an "Overdrive Off" button that switches between the two.

Others have taken a more "engineering" approach and just call OD D and call the overdrive lockout position the top gear number the transmission is allowed to use in that position.

It could be noted that the traditional way for the numbers to be used is exactly the same way, with the number indicating the highest gear the car allows itself to use. Since, however, some cars use the "2" selection as a "Winter" mode that actually starts the car in second gear (Not harmful in an automatic) in order to reduce the torque applied to the wheels.

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Post by MicroXcorp » Tue Jul 06, 2004 12:31 am

So drive (stand alone D) produces more power and it more like manual because the engine's RPM and car speed are directly related?

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Post by MicroXcorp » Tue Jul 06, 2004 12:44 am

I was writing the second reply so I didn't see your second reply. My dad has a 2000 Pontiac Trans Am, my mom she has a 98 or 99 Toyoto Camry.

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Post by IMBoring25 » Tue Jul 06, 2004 12:51 am

All definitely have overdriven transmissions.

The stand-alone D only locks out the top gear (in those vehicles, it should be fourth). Not any particularly more power or anything. Just locks out the top gear.

When you ask for power with the gas pedal, the transmission should downshift anyway, into the same gear it would have been in already if you had disabled the overdrive. You gain a little by not having the shift, but that's no reason to drive around in third all the time.

My official explanation is:
1) To keep the car from hunting if you drive for an extended time at the speed that's right on the boundary between top gear and the next one lower.
2) Engine braking on downhills.

In some vehicles, you can get a little more out of them shifting the automatic manually 1-2-D-OD, because you can force the vehicle to hold the gear longer than it would like to, but the gain is minimal, the risk is significant (Reverse is a bad thing to hit, for one thing), and some vehicles are actually slower when manually shifted. Then there are the automatics with paddles or +/- selections on the shifter that can be shifted manually with some benefit and, generally, failsafes to keep you from doing anything you don't want to do.

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Post by MicroXcorp » Tue Jul 06, 2004 1:13 am

Thank you for the explain, you helped me out alot. I appreciate it. :D

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Post by The YoYo Freak » Thu Jul 08, 2004 5:05 pm

Most automatics require you to hold the brake and push in a small button on the lever to go from drive to reverse, so you shouldn't have to worry about that. In my mom's Corolla, you can start in 'L', then just push the lever up to '2', and once again flick it up into 'D'. After that there is just the overdrive key on the side of the lever to get the final gear. It's not really something you want to do, as it puts major stress on the transmission, and it sounds really horrible, esp. on my mom's car.

Usually you want to avoid overdrive when you're puttering around in the mountains. Other than that the automatic should do it's thing - shift automatically.

Jared

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Post by oxxenking » Mon Jul 19, 2004 6:10 am

my moms toyota has 1 2 3 and D , 3 locks out D, which is our overdrive, if you cant find a circle D on your thingy then 3 is probably it, if there is no 3 and all you have is 1 2 and D then there is a very good change that is has a button to switch between overdrive and drive. unless your car/suv/truck sucks :/

thats just my opinion though about if it sucks or not.

I noticed in the toyota in 3 gives me acceleration and Good hill climbing (Guts) but D gives me REally good gas mileage. when im driving my moms car. im getting 21 miles per gallon IN A AUTOMATIC using D which is our Overdrive. bit only getting 17 in 3 which is our D,
our 2nd gear is for pure acceleration and really bad gas mileage. it revs the engine to near redline before auto shifting which is good for racing but it tops out in 3rd gear (i think im jus listing to the engine and i only heard it shift 2 times) and i had to put it manually back into 3 before it redlined.

me personally though i drive a manually and i try to stay away from my moms car as much as possible. so i dont have to worry too much about that drive and overdrive crap

i DO know 2nd and 1st gear are mainly used for hill braking dont think i dont know that. im just saying what i have found out whilst testing out my moms car for the last time. :) :twisted:
i could be wrong about everything i just said but correct me if im wrong.

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Post by markeemsz » Mon Jul 19, 2004 8:32 am

Yeah youre right . My cavalier has three speed automatic . 1 and 2 I use for engine braking everynow and then. Drive (D) is third gear. At 40 mph a solenoid in the transmission locks the transmission into third gear. This is in effect a type of overdrive for that transmission . This increases gas mileage when youre cruising. A common complaint is that when the solenoid goes bad it locks the tranny in third and wont release causing the car to stall out. If u unplug it instead of fixing it it lowers your gas mileage.

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Post by 96ragtop » Mon Jul 19, 2004 5:48 pm

How old is your cavalier? My mom has a 2002, with 1,2,3,D,R,P.
So I'm assuming 3 is drive, and D is overdrive? Not that it matters anymore...I drive her car maybe once a week if that.

Quick note about 1 : I used it a couple times in the winter when I couldn't get traction worth shit. I think this is because the engine can freely rev higher (just don't redline it). Plus it turns off the traction control (only works in 3 and D), which is a shitty worthless idea to begin with. And having it in 1 got me up the hill no problem, when in D it couldn't do anything...

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re:

Post by ReckLess » Tue Jul 20, 2004 1:12 am

NOooooooooooooooooooo whyYYYYYYYYYYYYYy... change to automatic ?
:twisted:

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Post by 96ragtop » Thu Jul 22, 2004 1:38 am

I don't think he changed to automatic if I understand correctly, only drove it in the meantime whilst his manual car was getting the clutch replaced.

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Post by MicroXcorp » Thu Jul 22, 2004 3:17 pm

right :wink: the heck with automatic, i'm tellin you man, it was boring, the only think i got to do was shift to (D) :lol: and the dang car shifts when it wants to shift (thats not good)

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