HELP WITH OVERDRIVE TRANSMISSION, I NEED TO KNOW WHAT OVERDRIVE DOES?? Options

[BlazedInMyCeli]

i recently purchased an automatic 97 celica ST hatchback. I have been wondering if most people leave there car in or out of overdrive? Any benefits to better mpg with overdrive??? what exactly does overdrive do?

[3SGTE-auto]

Red joker is right. Overdrive gear is gear #4. Its called od because its gear ratio is less than 1, which means it delivers more rpm to the final drive (differential) gear than the rpm of the engine. Turn off overdrive when hauling heavy loads, to help preserve the 4th gear in your transmission. OD off will mean you can only use gears 1,2&3. Otherwise, leave it enabled (due to is nature of being overdrive, it is therefore the gear that is more likely to get damaged from friction or physical stress). The U140 transmission in some late model corollas is a rare example of a fwd trans that has no overdrive gear: it's 4th gear is ratio of 1. And yet, the U140 and the A140 use almost the same rpm as each other in each gear. Its able to achieve this by using a different final drive ratio.

This post has been edited by 3SGTE-auto: Oct 16, 2008 - 7:00 AM