whats the meaning of an over drive transmission in a vehicle.?

Question

l want to buy a used car but the dealer said it has an over drive transmission. does anyone know the meaning of it

Answer 1

Generally speaking, overdrive (OD) is the highest gear in the transmission. Most automatic transmissions have three speeds and overdrive (fourth speed). Overdrive allows the engine to operate at a lower rpm for a given road speed. This allows the vehicle to realize better fuel efficiency, and often quieter operation on the highway. When you switch it on, you allow the transmission to shift into overdrive mode after the certain speed is reached (usually 70+ km/h ~ 45+ mph) depending on the load). When it is off, the transmission shifting is limited to the lower gears. For normal driving conditions, operation of the overdrive should be enabled only if the average speed is above 70 km/h (approx. 43 MPH).

It may be necessary to switch it off if the vehicle is being operated in a mountainous area.

The automatic transmission automatically shifts from OD to third gear when more load is present. When less load is present, it shifts back to OD. Under certain conditions, e.g.: driving uphill or towing a trailer, the transmission may "hunt" between OD and the third gear, shifting back and forth. In this case, switching it off can help the transmission to 'decide'. It may also be advantageous to switch it off if engine braking is desired, for example, driving downhill. The vehicle's owner's manual has information and procedures regarding such situations

Answer 2

The earlier days of over drive automatic transmissions was the "lock up" transmissions where they still had only three speeds or gears and when you reached roughly 30 MPH the torque convertor would lock up so that the ratio was 1:1 with the engine. This means that for every one revolution of the engine the transmission would revolve the same so that there was no slipping possible within the torque convertor. This brought the miles per gallon up The transmission controls the engine RPM's and the lower the RPM's the more miles per gallon.

Most newer cars have at least four speeds or gears in the transmission, some now have six, and when the car reaches a speed of around 40 MPH the transmission will shift into the highest gear or over drive. There is still an electric solenoid inside the transmission that engages this over drive function just like the older 3-speed lock up transmissions. The difference is the gear ratios leading up to the fourth, fifth, or sixth gear before the "lock up" or over drive engages.

So long as there is sufficient torque and energy created by the engine revolutions per minute (RPM's) the transmission will shift from gear to gear allowing the best possible fuel economy at each speed up to and including highway speeds.

The only time that you have to concern yourself with placing the transmission in a lower gear, or any gear other than DRIVE, is if you are towing a heavy trailer and you are going up or down a steep grade or hill. However, most transmissions will down shift as necessary for the cars speed going up hill. Going down hill you have to shift down so the transmission will use the engine to slow the car down since the brakes will quickly over heat and lose there ability to slow and or stop the car.

The same is true with stick shift or manual transmissions.

Good Luck!

Answer 3

Thsi is what an overdrive tranmission is. All transmissions manual and auto without overdrive has a final drive at 1:1 meaning the output shaft on the transmission turns at the same speed as the engine's crankshaft. This would be 4th gear in a four speed manual and third gear in a 3 speed automatic. A overdrive transmission has a extra gear that is a higher gear ratio usually around 1: .75 This would be 4th gear in an automatic and 5th gear in a manual. This meens the output shaft on the transmission turns faster that the engine crankshaft. Which meens it turns the drive wheels faster at a lower engine speed. Which this meens your engine doesn't burn as much fuel. Hope you understand a little better.

Answer 4

Very simple. An Over Drive Transmission is a transmission with over drive in it. Its an extra gear that allows you to lower your RPM while driving high speeds. Saves you some gas miles. And with the price of gas I wont hesitate to take that option. High ways speeds is on average around 55

Answer 5

You just need to find out how to drive one. Whether it be through a driving school or finding someone. Driving manual isn't that hard. I learned to drive stick before I drove automatic. It's all about feeling and hearing the acceleration of the vehicle.

Answer 6

Overdrive is the gear that is used @ speeds of normally over 40mph and it is a fuel saver in cars w/ automatic transmissions.

Answer 7

Overdrive is good. Almost all cars have them now. It allows the engine to turn very slow for good gas mileage. Not much power with this gear though. Used mainly for freeway driving.

Answer 8

Overdrive is like a top gear. It lets you get engine shaft power without gearing as such, engine power goes straight to the rearend without getting the ratio reduced like in first, second, third or fourth gear

Answer 9

trannys have several gears that will shift while it is driven. when the highest gear has shifted (overdrive) the rpm's will drop which will make the engine run cooler and save on gas mileage.

Answer 10

Over drive is a extra half ratio gear. designed to aid it fuel economy.