overdrive?
05-29-2009, 10:53 PM
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overdrive?
ok so I got a N00b question about the 5spd getrag in our car. in the description of our tranny, its described as a 5 speed manual with Overdrive. what exactly does "overdrive" mean?? is there sort of a minimal 6th gear so to speak? or does it just describe the final drive ratio in top gear?? the main reason I"m wondering, is when I'm using cruse control, and the highway starts to go down hill fairly steeply, at a certain point the car seems to jump very slightly as if it just dropped down a gear on its own in an effort to maintain the set speed. I'm not imagening this little jump! LoL
so is there an automatic 6th gear in there somewhere for fuel effeciency or what? just wondering. thanks for any replys in advance! at least the ones that aren't flaming me for the dumb question!
so is there an automatic 6th gear in there somewhere for fuel effeciency or what? just wondering. thanks for any replys in advance! at least the ones that aren't flaming me for the dumb question!
05-30-2009, 12:21 AM
#2
overdrive refers to the gear ratio. when your gear ratio is anything less than 1:1 (1 turn of the input shaft = one turn of the output shaft) its overdrive. for example, we have a .70:1 5th gear, meaning that if you turn the input shaft 0.7 turns the output shaft will turn 1 turn, this is an overdrive ratio.
in the cobalt f35 (which is made by saab, not getrag) 4th and 5th gears are "overdrive", 4th gear being .89:1 and 5th being .70:1. compare that to 3rd gear being 1.18:1, that is technically an underdrive ratio, however nobody refers to it as that.
what happens when going down the hill with cruise on and the car seems like its holding back like you dropped a gear is just the pcm shutting the fuel off to the engine. by doing this the car can maintain speed without speeding up while coasting. it also does help with fuel economy.
in the cobalt f35 (which is made by saab, not getrag) 4th and 5th gears are "overdrive", 4th gear being .89:1 and 5th being .70:1. compare that to 3rd gear being 1.18:1, that is technically an underdrive ratio, however nobody refers to it as that.
what happens when going down the hill with cruise on and the car seems like its holding back like you dropped a gear is just the pcm shutting the fuel off to the engine. by doing this the car can maintain speed without speeding up while coasting. it also does help with fuel economy.
05-30-2009, 02:15 AM
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cool! thanks sharkey! I'm fairly well educated when it comes to cars, but don't have much of a clue about gear ratio's. thanks for the reply! now I guess I know everything! LOL J/K
thanks again!
thanks again!
05-30-2009, 09:35 AM
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overdrive refers to the gear ratio. when your gear ratio is anything less than 1:1 (1 turn of the input shaft = one turn of the output shaft) its overdrive. for example, we have a .70:1 5th gear, meaning that if you turn the input shaft 0.7 turns the output shaft will turn 1 turn, this is an overdrive ratio.
in the cobalt f35 (which is made by saab, not getrag) 4th and 5th gears are "overdrive", 4th gear being .89:1 and 5th being .70:1. compare that to 3rd gear being 1.18:1, that is technically an underdrive ratio, however nobody refers to it as that.
what happens when going down the hill with cruise on and the car seems like its holding back like you dropped a gear is just the pcm shutting the fuel off to the engine. by doing this the car can maintain speed without speeding up while coasting. it also does help with fuel economy.
in the cobalt f35 (which is made by saab, not getrag) 4th and 5th gears are "overdrive", 4th gear being .89:1 and 5th being .70:1. compare that to 3rd gear being 1.18:1, that is technically an underdrive ratio, however nobody refers to it as that.
what happens when going down the hill with cruise on and the car seems like its holding back like you dropped a gear is just the pcm shutting the fuel off to the engine. by doing this the car can maintain speed without speeding up while coasting. it also does help with fuel economy.
05-30-2009, 08:29 PM
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overdrive refers to the gear ratio. when your gear ratio is anything less than 1:1 (1 turn of the input shaft = one turn of the output shaft) its overdrive. for example, we have a .70:1 5th gear, meaning that if you turn the input shaft 0.7 turns the output shaft will turn 1 turn, this is an overdrive ratio.
in the cobalt f35 (which is made by saab, not getrag) 4th and 5th gears are "overdrive", 4th gear being .89:1 and 5th being .70:1. compare that to 3rd gear being 1.18:1, that is technically an underdrive ratio, however nobody refers to it as that.
what happens when going down the hill with cruise on and the car seems like its holding back like you dropped a gear is just the pcm shutting the fuel off to the engine. by doing this the car can maintain speed without speeding up while coasting. it also does help with fuel economy.
in the cobalt f35 (which is made by saab, not getrag) 4th and 5th gears are "overdrive", 4th gear being .89:1 and 5th being .70:1. compare that to 3rd gear being 1.18:1, that is technically an underdrive ratio, however nobody refers to it as that.
what happens when going down the hill with cruise on and the car seems like its holding back like you dropped a gear is just the pcm shutting the fuel off to the engine. by doing this the car can maintain speed without speeding up while coasting. it also does help with fuel economy.
The F23 also has 2 overdrive gears, although 4th is just .2 under 1.
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