What is "overdrive"?

"Jake - Has Bad Luck So You Don't Have To" (murdersofa)
03/19/2016 at 22:28 • Filed to: None

I know what an overdrive gear is, so I think, but the definition gets muddied by such phrases as “it’s a four speed transmission. With overdrive” or “Yeah, it’s got five speeds and an overdrive”, as well as the presence of “O/D on/off” switches. Are these people getting fooled by the torque converter lockup into thinking their 5-speed actually has 5 speeds plus a mythical “overdrive” gear?

DISCUSSION (10)

DrJohannVegas > Jake - Has Bad Luck So You Don't Have To
03/19/2016 at 22:30

It means that the output shaft rotates faster than the input shaft.

Edit: Hit publish before I was done. Anyway...

But people don’t know how fast the shafts are rotating. Heck, the relationship between crankshaft and wheels isn’t discernable. So, I think you are right about converter lockup. Folks don’t notice it in lower gears, but in top gear, they do.

Edit 2: I guess it’s also possible to have a single-speed gearbox with overdrive, so it’s doubly silly.

Arch Duke Maxyenko, Shit Talk Extraordinaire > Jake - Has Bad Luck So You Don't Have To
03/19/2016 at 22:31

http://www.ford-trucks.com/forums/attachm…

DrJohannVegas > Arch Duke Maxyenko, Shit Talk Extraordinaire
03/19/2016 at 22:35

Nice.

Jake - Has Bad Luck So You Don't Have To > Arch Duke Maxyenko, Shit Talk Extraordinaire
03/19/2016 at 22:36

Explain like I’m five. Is that a gearbox that attaches to the back of the trans to raise the final drive ratio or something? Or is it an engagable version of that which essentially makes your top gear into an overdrive?

If only EssExTee could be so grossly incandescent > Jake - Has Bad Luck So You Don't Have To
03/19/2016 at 22:40

Nowadays overdrive is just the top gear or two in the transmission, one with a ratio lower than 1:1, but in days of yore cars actually had a separate overdrive unit at the back of the transmission. A three speed box with a two speed overdrive means you have six available ratios because you now have a Hi and Lo version of each main gear.

If only EssExTee could be so grossly incandescent > Jake - Has Bad Luck So You Don't Have To
03/19/2016 at 22:51

On a modern car the overdrive button just locks you out of your top gear, to keep the car from constantly “hunting” between gears when under load. Our old CRV did that to me once when climbing a steep hill while fully loaded, it would hit the shift point in 3rd, so then it would go into 4th but then it didn’t have enough power and applying throttle hit the kickdown switch and then it would shift back into 3rd and so on... Clicking the OD button fixed that.

crowmolly > Jake - Has Bad Luck So You Don't Have To
03/19/2016 at 23:02

It is a gear splitter. Look up Gear Vendors. Or Hone-O-Drive.

This is what was used to make the Corvette 4+3, which was a Super T-10 with a bolt on splitter.

The O/D off will lock out any gear that’s numerically lower than 1:1 in some transmissions. Sometimes it’s also part of “tow/haul” mode as towing in OD can be bad.

jimz > Jake - Has Bad Luck So You Don't Have To
03/19/2016 at 23:03

“overdrive” means the transmissions output shaft rotates faster than the input shaft. any car or light truck transmission with four or more gears has at least one overdrive ratio. it’s pointless to talk about it in 2016.

Liam Farrell > Jake - Has Bad Luck So You Don't Have To
03/19/2016 at 23:11

Been thinking of getting one for the Land Rover, maybe try and increase top speed by at least 10. It's either that or sell our 05 expedition and then do a LS swap.

BloodlessWeevil > Jake - Has Bad Luck So You Don't Have To
03/20/2016 at 11:20

In ye olde days the top gear of a transmission was 1:1. All the other gears were reductions. Another ratio was added “above” the top gear to decrease engine speed during constant speed cruising.

So a four speed transmission with an overdrive ratio would give better fuel economy than one without. However, it is not a five speed transmission.

Overdrive has nothing whatsoever to do with locking torque converters.