[the_enemy_within]

I always wondered this, what does overdrive do actually, does it make any difference when daily driving????

thanks,

 

[OmniFocus]

It is 4th gear... That's it!

The O/D button turns it off so that you drive along in 3rd gear... on some vehicles it also changes the shift pattern on gears 1-3 to downshift more aggressively as well as hold each gear a little longer before upshifting.

 

[orndog]

Overdrive = taller gear. Supposed to be higher than a 1:1 ratio I think. Anyway, it increases mpg. Turning it off is for towing, high altitude, steep hills (to avoid the car hunting between gears) and stuff. The towing part is why it might shift more agressively, meaning faster shifts.

 

[Fokyl]

I have an automatic ZX3. From a dead stop as you accelerate you can count 5 different gear ratios. That is,there is a distinct time when you know your in 1st, 2nd, 3rd, 4th then an upshift to OD. What have you guys been feeling. So far I have not heard any comments on this 5th gear.
Anyway, besides the slight softness of the auto with out my chip (92 octane= >$), I do feel pretty good about being able to feel those 5 speeds

...

 

[orndog]

Originally posted by Fokyl:
I have an automatic ZX3. From a dead stop as you accelerate you can count 5 different gear ratios. That is,there is a distinct time when you know your in 1st, 2nd, 3rd, 4th then an upshift to OD. What have you guys been feeling. So far I have not heard any comments on this 5th gear.
Anyway, besides the slight softness of the auto with out my chip (92 octane= >$), I do feel pretty good about being able to feel those 5 speeds

...

<font size="2" face="Verdana, Arial">I'll assume you're joking?
You have 4 speeds in your auto in case you're not. You're feeling the torque converter locking.

 

[MUTTLEE]

That extra shift you "feel" is your torque converter locking up. It does this so the engine and tranny are "at one" to increase mileage too; no slippage.

 

[proxemac]

From NRMA:

OVERDRIVE
Supplementary transmission mounted between a gearbox and final drive. It raises the drive shaft's speed of rotation relative to the gearbox output shaft, changing the final drive ratio.

OVERDRIVE GEAR RATIO
Additional gear ratio in a transmission which, when engaged, causes the gearbox output shaft to rotate more slowly than the crankshaft.

So it sounds likes overdrive on an automatic is essentially a way to recreate the functionality of having a smaller gear ratio but without adding another gear in the gearbox.

[ 02-09-2003, 06:54 PM: Message edited by: proxemac ]

 

[JP]

Sounds(reads) like there is a lot of misinformation.

Overdrive gear is just any gear ratio less than 1.00

The O/D off button locks out 4th gear on an auto.
4th gear on an auto is the overdrive gear.

5th gear on a Focus is overdrive.

SVTF does not have an overgrive gear...however, the final drive gear in 5th (1.33) and 6th (1.08) is 2.88 so when multiplied by the trans gear ratio acts like an overdrive.

Typical 5th or 4th(auto) gear ratio is 0.70ish and final drive is 4.00 ish so effective engine rev/halfshaft rev ratio is 2.80:1