over drive
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over drive
how dose over drive work.... im opretty sure i got it right, but i have a little doubt.
I think over drive is not even a gear inside the transmission...meaning, that once you shift into 5th (overdrive) in a truck, the drive shaft is spining at the engines rmp and the transmission is not really doing anything, the gear ratio is 1:1 through the transmission and the only reduction of engine speed to wheel is the finaldrive...or rear axle gears.
correct me if im wrong,
I think over drive is not even a gear inside the transmission...meaning, that once you shift into 5th (overdrive) in a truck, the drive shaft is spining at the engines rmp and the transmission is not really doing anything, the gear ratio is 1:1 through the transmission and the only reduction of engine speed to wheel is the finaldrive...or rear axle gears.
correct me if im wrong,
Posting Guru
Joined: Jun 1999
Posts: 2,404
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From: Everett, Wa
It is a gear in the tranny. What overdirve is, is that the engine turns slower, the wheels turn faster. When you see an overdrive of say .87:1 it means that for ever .87 revolution of engine turns the drive shaft turns 1 revolution.
Post Fiend
Joined: Jun 2004
Posts: 8,147
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From: Joppa, Maryland
To add to that, generally speaking in say a 5 speed tranny the 4th gear will be 1:1 essentially a direct drive. Or 3rd in a 4 speed, etc, etc. Some vehicles even have two overdrives for more economy (the new allison tranny behind the chebby duramax and the corvette are two i can think of off the top of my head.
Post Fiend
Joined: Jul 2005
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From: Durant, OK (SOSU)
A lot of high performance European vehicles (Lambos and the like) have THREE overdrives!!! They need it to get to those top end speeds.
In older cars, overdrive was it's own seperate unit behind the tranny. In modern vehicles, it's just another gear. As said, it just causes the output shaft of the tranny (read:driveshaft) to spin faster than the input shaft (read:crankshaft). Better MPG, etc.
1:1 wouldn't be an overdrive gear since the engine is spinning at the same speed as the driveshaft(s).
In a .87 OD, if the engine is doing 2000 RPM, the driveshaft is doing 2299 RPM (or so...). Assuming my rear end ratio, 3.08, the tires are spinning at 746.4 RPM. Remember, non-stock tires alter the final drive ratio, but that's pretty accurate.
Hope it helps, I was on here just a while back asking if overdrive meant the engine was spinnin' slower than the driveshaft, so I've heard this all before! lol. Why aren't the other gears called underdrive? Food for thought...
In older cars, overdrive was it's own seperate unit behind the tranny. In modern vehicles, it's just another gear. As said, it just causes the output shaft of the tranny (read:driveshaft) to spin faster than the input shaft (read:crankshaft). Better MPG, etc.
1:1 wouldn't be an overdrive gear since the engine is spinning at the same speed as the driveshaft(s).
In a .87 OD, if the engine is doing 2000 RPM, the driveshaft is doing 2299 RPM (or so...). Assuming my rear end ratio, 3.08, the tires are spinning at 746.4 RPM. Remember, non-stock tires alter the final drive ratio, but that's pretty accurate.
Hope it helps, I was on here just a while back asking if overdrive meant the engine was spinnin' slower than the driveshaft, so I've heard this all before! lol. Why aren't the other gears called underdrive? Food for thought...
