towing question overdrive
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Senior Member
Joined: Jun 2011
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From: Texas
This is from what I understand...
Our engines are a 4 speed with overdrive so basiccally 5 overall speeds which is the transmission gears. Overdrive reduces the RPMs of the crankshaft when at a steady speed for more efficient MPGs which is done by the transmission gears. When towing a good amount of weight the transmission will continuously lock up in overdrive and unlock causing it to work significantly harder throughout the trip which is why you should turn overdrive off so the transmission doesnt fail prematurally from continuously shifting in and out of overdrive.
Anyone else can ellaborate where I may be wrong or off a little.
Our engines are a 4 speed with overdrive so basiccally 5 overall speeds which is the transmission gears. Overdrive reduces the RPMs of the crankshaft when at a steady speed for more efficient MPGs which is done by the transmission gears. When towing a good amount of weight the transmission will continuously lock up in overdrive and unlock causing it to work significantly harder throughout the trip which is why you should turn overdrive off so the transmission doesnt fail prematurally from continuously shifting in and out of overdrive.
Anyone else can ellaborate where I may be wrong or off a little.
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Joined: Jul 2011
Posts: 258
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The 4r75w that is in our trucks is a 4 speed. That includes "overdrive"
Overdrive is a term used to describe any gear ratio shorter or less than 1:1.
So 3rd gear is 1:1. That means once your torque converter has stalled, the crankshaft speed RPM is the same as the transmission output shaft.
Gears taller or higher than 1:1 are 1st and 2nd in our case. The crank spins faster than output shaft.
Overdrive is 4th gear. The ratio there is probably 0.75:1 or something like that. So the crank spins slower than the output shaft to save fuel and keep noise down, at the expense of available power to do lower RPM.
So disabling OD keeps your transmission out of 4th gear, to keep more power available to pulling loads.
What the above poster was describing is called the torque converter lockup clutch. (TCC)
This further decreases RPM by removing the hydraulic slip in the torque converter.
Disabling OD does not disable the TCC, an you'll still get lockup at light loads in 2nd and 3rd gear.
Any transmission with 6 or more gears generally have 2 OD gears.
Overdrive is a term used to describe any gear ratio shorter or less than 1:1.
So 3rd gear is 1:1. That means once your torque converter has stalled, the crankshaft speed RPM is the same as the transmission output shaft.
Gears taller or higher than 1:1 are 1st and 2nd in our case. The crank spins faster than output shaft.
Overdrive is 4th gear. The ratio there is probably 0.75:1 or something like that. So the crank spins slower than the output shaft to save fuel and keep noise down, at the expense of available power to do lower RPM.
So disabling OD keeps your transmission out of 4th gear, to keep more power available to pulling loads.
What the above poster was describing is called the torque converter lockup clutch. (TCC)
This further decreases RPM by removing the hydraulic slip in the torque converter.
Disabling OD does not disable the TCC, an you'll still get lockup at light loads in 2nd and 3rd gear.
Any transmission with 6 or more gears generally have 2 OD gears.
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Joined: Dec 2011
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From: Tyndall AFB
The 4r75w that is in our trucks is a 4 speed. That includes "overdrive"
Overdrive is a term used to describe any gear ratio shorter or less than 1:1.
So 3rd gear is 1:1. That means once your torque converter has stalled, the crankshaft speed RPM is the same as the transmission output shaft.
Gears taller or higher than 1:1 are 1st and 2nd in our case. The crank spins faster than output shaft.
Overdrive is 4th gear. The ratio there is probably 0.75:1 or something like that. So the crank spins slower than the output shaft to save fuel and keep noise down, at the expense of available power to do lower RPM.
So disabling OD keeps your transmission out of 4th gear, to keep more power available to pulling loads.
What the above poster was describing is called the torque converter lockup clutch. (TCC)
This further decreases RPM by removing the hydraulic slip in the torque converter.
Disabling OD does not disable the TCC, an you'll still get lockup at light loads in 2nd and 3rd gear.
Any transmission with 6 or more gears generally have 2 OD gears.
Overdrive is a term used to describe any gear ratio shorter or less than 1:1.
So 3rd gear is 1:1. That means once your torque converter has stalled, the crankshaft speed RPM is the same as the transmission output shaft.
Gears taller or higher than 1:1 are 1st and 2nd in our case. The crank spins faster than output shaft.
Overdrive is 4th gear. The ratio there is probably 0.75:1 or something like that. So the crank spins slower than the output shaft to save fuel and keep noise down, at the expense of available power to do lower RPM.
So disabling OD keeps your transmission out of 4th gear, to keep more power available to pulling loads.
What the above poster was describing is called the torque converter lockup clutch. (TCC)
This further decreases RPM by removing the hydraulic slip in the torque converter.
Disabling OD does not disable the TCC, an you'll still get lockup at light loads in 2nd and 3rd gear.
Any transmission with 6 or more gears generally have 2 OD gears.
