OD HELP
Thread Starter
5th Gear Member
Joined: Nov 2007
Posts: 4,286
From: Georgia
OD HELP
alright now i want someone to really explain this to me because now i am confused... i had always thought that OD was a fifth gear, for highway, but when i was driving home from work today i was analyzing it and if i had it off, at 50 mph, my rpm's would sit at 2200 in third gear. when i turned it on, it would shift into fourth gear and my rpm's would drop... i don't understand, what does OD do to my computer? the thing wouldn't even shift either.. i would go up to 60 and slow back down and either way at 60 or 50 it would stay in 3rd and never shift into fourth while the od is off... can someone explain it to me?
4th Gear Member
Joined: Jul 2006
Posts: 1,035
From: Phoenix
RE: OD HELP
Read this article it should help you understand http://auto.howstuffworks.com/automa...nsmission3.htm
5th Gear Member
Joined: Jul 2006
Posts: 4,951
From: CT
RE: OD HELP
OD on the 4r70w is a fourth gear. Hence the 4 in the tranny code name.
The way it works, if your tranny has 4 forward gears, and a reverse gear. Each gear has a ratio. I don't know the ratios for the 4r70w specifically, but I'll just make up numbers.
Say first gear is a 4:1 ratio. That means the torque produced by the engine is multiplied by four. First gear always has a steep ratio, since it's the gear used to move the car from a dead stop. Second gear would then be something like 3 or 2.8:1 or something like that. Again, just making up numbers. Second gear still needs torque since it's an accellerating gear, but not as much since you're already moving. Third gear can be, let's say 1.4:1. Still multiplying torque, but not so much as first and second. Then finally, you have an overdrive gear. An overdrive ratio is usually something like 0.75:1. This makes it so your engine spins at a lower RPM but still keeps you moving, but saving you gas. Plus, it only take somewhere like 15-20hp to keep the average sized car moving steadily at 65-70mph. That's why highway mileage is better.
Hopefully that makes sense.
Oh, and also, if you didn't know it, OD is always on when you start the car, and the tranny will always shift into it after third unless you turn it off. And if you put the shifter into the 1 or 2 position, it doesn't mean it's in that gear, it just means that that is the highest gear it will shift to. So if you put your car in 1, it will just stay in first gear and never shift. If you put it in two, it will only shift to second. If you put it in D, it will shift all the way up to OD unless you press the button, then it will only shift to third.
OK, I think that should explain everything. The manual transmissions work the same way, too (well, as far as the ratio thing goes). 4 speeds 4th is OD, 5 speeds 5 is OD, it's 6 speeds where some trannies have 6 as an OD and some have 5 and 6, where they basically have a double OD.
OK, done rambling now.
The way it works, if your tranny has 4 forward gears, and a reverse gear. Each gear has a ratio. I don't know the ratios for the 4r70w specifically, but I'll just make up numbers.
Say first gear is a 4:1 ratio. That means the torque produced by the engine is multiplied by four. First gear always has a steep ratio, since it's the gear used to move the car from a dead stop. Second gear would then be something like 3 or 2.8:1 or something like that. Again, just making up numbers. Second gear still needs torque since it's an accellerating gear, but not as much since you're already moving. Third gear can be, let's say 1.4:1. Still multiplying torque, but not so much as first and second. Then finally, you have an overdrive gear. An overdrive ratio is usually something like 0.75:1. This makes it so your engine spins at a lower RPM but still keeps you moving, but saving you gas. Plus, it only take somewhere like 15-20hp to keep the average sized car moving steadily at 65-70mph. That's why highway mileage is better.
Hopefully that makes sense.
Oh, and also, if you didn't know it, OD is always on when you start the car, and the tranny will always shift into it after third unless you turn it off. And if you put the shifter into the 1 or 2 position, it doesn't mean it's in that gear, it just means that that is the highest gear it will shift to. So if you put your car in 1, it will just stay in first gear and never shift. If you put it in two, it will only shift to second. If you put it in D, it will shift all the way up to OD unless you press the button, then it will only shift to third.
OK, I think that should explain everything. The manual transmissions work the same way, too (well, as far as the ratio thing goes). 4 speeds 4th is OD, 5 speeds 5 is OD, it's 6 speeds where some trannies have 6 as an OD and some have 5 and 6, where they basically have a double OD.
OK, done rambling now.
5th Gear Member
Joined: Mar 2007
Posts: 3,791
From: Cary/Charlotte, NC
RE: OD HELP
4r70w is a 4 speed, 3 gears + an over drive gear along with a reverse. the od uses the torque converter as a gear. when you press the OD button is will put you in third which is a 1 to 1 ratio.
5th Gear Member
Joined: Jul 2007
Posts: 2,363
From:
RE: OD HELP
ORIGINAL: defconfire
4r70w is a 4 speed, 3 gears + an over drive gear along with a reverse. the od uses the torque converter as a gear. when you press the OD button is will put you in third which is a 1 to 1 ratio.
4r70w is a 4 speed, 3 gears + an over drive gear along with a reverse. the od uses the torque converter as a gear. when you press the OD button is will put you in third which is a 1 to 1 ratio.
a torque converter is a fluid coupling and in no way is a gear.
5th Gear Member
Joined: Jul 2007
Posts: 2,363
From:
RE: OD HELP
automatics use planetary gearsets for gears, clutches hold certain parts such as the planet gear, sun gear or pinions to determine the gear ratios and reverse. maybe your thinking of the lockup clutch. inod the lockup clutch should engage which locks the crankshaft to the input shaft of the transmission allowing the automatic transmission to be more efficient by eliminating the slip of the torque converter.
5th Gear Member
Joined: Mar 2007
Posts: 3,791
From: Cary/Charlotte, NC
RE: OD HELP
OK so the od is a physical gear i didnt know that. I knew about the locking in tq converters but i genuinely thought that the 4th gear was some how derived from the torque converter. then again I dont know much about autos.
TO EVERYONE IGNORE ANY OF MY PREVIOUS POSTS IN THIS THREAD
TO EVERYONE IGNORE ANY OF MY PREVIOUS POSTS IN THIS THREAD
5th Gear Member
Joined: Jul 2007
Posts: 2,363
From:
RE: OD HELP
yea its kool i didnt know much about automatics either until i took a class and learned alot, it helps alot when you have the parts in your hand and have actually built one. until you do that it would be pretty hard to understand because it is pretty complicated.
Thread Starter
5th Gear Member
Joined: Nov 2007
Posts: 4,286
From: Georgia
RE: OD HELP
ORIGINAL: Xemeth
OD on the 4r70w is a fourth gear. Hence the 4 in the tranny code name.
The way it works, if your tranny has 4 forward gears, and a reverse gear. Each gear has a ratio. I don't know the ratios for the 4r70w specifically, but I'll just make up numbers.
Say first gear is a 4:1 ratio. That means the torque produced by the engine is multiplied by four. First gear always has a steep ratio, since it's the gear used to move the car from a dead stop. Second gear would then be something like 3 or 2.8:1 or something like that. Again, just making up numbers. Second gear still needs torque since it's an accellerating gear, but not as much since you're already moving. Third gear can be, let's say 1.4:1. Still multiplying torque, but not so much as first and second. Then finally, you have an overdrive gear. An overdrive ratio is usually something like 0.75:1. This makes it so your engine spins at a lower RPM but still keeps you moving, but saving you gas. Plus, it only take somewhere like 15-20hp to keep the average sized car moving steadily at 65-70mph. That's why highway mileage is better.
Hopefully that makes sense.
Oh, and also, if you didn't know it, OD is always on when you start the car, and the tranny will always shift into it after third unless you turn it off. And if you put the shifter into the 1 or 2 position, it doesn't mean it's in that gear, it just means that that is the highest gear it will shift to. So if you put your car in 1, it will just stay in first gear and never shift. If you put it in two, it will only shift to second. If you put it in D, it will shift all the way up to OD unless you press the button, then it will only shift to third.
OK, I think that should explain everything. The manual transmissions work the same way, too (well, as far as the ratio thing goes). 4 speeds 4th is OD, 5 speeds 5 is OD, it's 6 speeds where some trannies have 6 as an OD and some have 5 and 6, where they basically have a double OD.
OK, done rambling now.
OD on the 4r70w is a fourth gear. Hence the 4 in the tranny code name.
The way it works, if your tranny has 4 forward gears, and a reverse gear. Each gear has a ratio. I don't know the ratios for the 4r70w specifically, but I'll just make up numbers.
Say first gear is a 4:1 ratio. That means the torque produced by the engine is multiplied by four. First gear always has a steep ratio, since it's the gear used to move the car from a dead stop. Second gear would then be something like 3 or 2.8:1 or something like that. Again, just making up numbers. Second gear still needs torque since it's an accellerating gear, but not as much since you're already moving. Third gear can be, let's say 1.4:1. Still multiplying torque, but not so much as first and second. Then finally, you have an overdrive gear. An overdrive ratio is usually something like 0.75:1. This makes it so your engine spins at a lower RPM but still keeps you moving, but saving you gas. Plus, it only take somewhere like 15-20hp to keep the average sized car moving steadily at 65-70mph. That's why highway mileage is better.
Hopefully that makes sense.
Oh, and also, if you didn't know it, OD is always on when you start the car, and the tranny will always shift into it after third unless you turn it off. And if you put the shifter into the 1 or 2 position, it doesn't mean it's in that gear, it just means that that is the highest gear it will shift to. So if you put your car in 1, it will just stay in first gear and never shift. If you put it in two, it will only shift to second. If you put it in D, it will shift all the way up to OD unless you press the button, then it will only shift to third.
OK, I think that should explain everything. The manual transmissions work the same way, too (well, as far as the ratio thing goes). 4 speeds 4th is OD, 5 speeds 5 is OD, it's 6 speeds where some trannies have 6 as an OD and some have 5 and 6, where they basically have a double OD.
OK, done rambling now.