Question about OD
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TECH Apprentice
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Question about OD Its not quite related to the specific auto trannies ther our f-bodies or corvettes have but still related to auto's. For just about all auto trannies, isn't OD basically the torq converter locking up in 4th or 5th (however gears the tranny has)?. This dude keeps telling that its an extra gear so now I'm confused.
No, Overdrive is an extra gear like the guy says. In our cars, it is 4th gear. It gets its name because its "overdriven", or a less than 1:1 ratio (around .70 or so). TCC lockup stops converter slippage and doesn't change your gearing.
Joined: Jul 2006
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From: Oshawa (Home of the 5th-gen)
Old TH350's and TH400's were 3-speed transmissions. The newer 4L60E's and 4L80E's are the over-drive versions of those 350's/400's respectively, by the addition of 4th gear
.
And when talking about a 6-speed, their 1:1 gear is 4th (where in the auto it's 3rd gear). Overdrive is both 5th and 6th gear (0.74:1 and 0.50:1) where the auto only has 0.70:1. BUT, the new 6-speed automatic that GM now has in the Corvettes (and I'm sure they'll be surfacing in other cars) actually has a 1.15:1 ratio in 4th gear (there is no 1:1) and then 2 over-drive gears (5th and 6th) after that.
Torque converter lock-up "feels" like another shift, but it's not.
.And when talking about a 6-speed, their 1:1 gear is 4th (where in the auto it's 3rd gear). Overdrive is both 5th and 6th gear (0.74:1 and 0.50:1) where the auto only has 0.70:1. BUT, the new 6-speed automatic that GM now has in the Corvettes (and I'm sure they'll be surfacing in other cars) actually has a 1.15:1 ratio in 4th gear (there is no 1:1) and then 2 over-drive gears (5th and 6th) after that.
Torque converter lock-up "feels" like another shift, but it's not.
TECH Senior Member
Joined: Apr 2002
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From: So.Cal.
The 4L60E gear ratios are:
1st=3.059
2nd=1.625
3rd=1.000
4th=0.696
The ratio is the number of revolutions the transmission input makes for 1 revolution of its output;
4th is "overdriven", the input turns less than the output:
i.e. input makes 0.696 of a revolution, output makes 1 complete rev.
And this is regardless of TCC lockup.
1st=3.059
2nd=1.625
3rd=1.000
4th=0.696
The ratio is the number of revolutions the transmission input makes for 1 revolution of its output;
4th is "overdriven", the input turns less than the output:
i.e. input makes 0.696 of a revolution, output makes 1 complete rev.
And this is regardless of TCC lockup.
Joined: Jul 2006
Posts: 381
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From: Oshawa (Home of the 5th-gen)
Originally Posted by joecar
And this is regardless of TCC lockup.
. If you're talking strictly input shaft of tranny to output shaft, then yes. But if you compare engine RPM to input shaft RPM, until you hit lock-up, there will pretty much always be a loss of RPM through the TQ converter. TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
Originally Posted by Cap'n Pete
Well, yes and no. If you're talking strictly input shaft of tranny to output shaft, then yes. But if you compare engine RPM to input shaft RPM, until you hit lock-up, there will pretty much always be a loss of RPM through the TQ converter.
. If you're talking strictly input shaft of tranny to output shaft, then yes. But if you compare engine RPM to input shaft RPM, until you hit lock-up, there will pretty much always be a loss of RPM through the TQ converter.
Originally Posted by joecar
The ratio is the number of revolutions the transmission input makes for 1 revolution of its output;
4th is "overdriven", the input turns less than the output:
i.e. input makes 0.696 of a revolution, output makes 1 complete rev.
And this is regardless of TCC lockup.
4th is "overdriven", the input turns less than the output:
i.e. input makes 0.696 of a revolution, output makes 1 complete rev.
And this is regardless of TCC lockup.
