What Is Overdrive???

[Rogue9]

Alright so I thought it was one thing... but an article I read said otherwise so could someone please clear up what overdrive is and does for me? thanks.

[ViperGTSR]

OD is your final gas saving gear, and easier on the engine

[iceman]

4th gear for our cars... when you are in D you are enabling overdrive.

[VaGT]

Some SUVs/Trucks have a button to disable... or a gear that does not allow the car to go into OD.. for hauling purposes.

[Rogue9]

ok so how does that work on a standard?? it means that's the 5th gear? last gear?

cause I was reading... one of the popular mags (forgot if it's sci or mech, I think it's the one with the vette on the cover)
They've made an alternative, bolt-on torque tube that permits overdrive to be used after every gear.

the article if Iremember says something like if overdrive was used with every gear then there'd be 8 gears. (I think it's the 4 speed auto vette) so the new torque tube makes the thing into 8 shifts.
so someone more technically inclined want to enlighten me?

[iceman]

Our overdrive is 4th gear.. i.e. drive. If you want to keep in third gear, then pick 3 on your gear selector.

[UNCTYPE-S]

how big is the difference between D and 3. i drive in D all the time. I never use 3. doesnt one of them give the car a quicker step, but also uses more gas. can someone explain the difference.

[Macleod52]

I would say Overdrive is usually the highest gear. In our cars it's "D" in my dad's 90 truck it was "D" with a box around it. Older vehicles did not come equipped with them and they were just another gear. I believe it just uses a different gear ratio or something? Don't know squat about tranny's so yeah.

The purpose of OD is for saving gas and perhaps less tear on the engine/tranny. I'll use our car as an example. If you are traveling at 55mph our car, in 3rd gear, is around 22-2500rpms (i think?!?!). Now, when you throw your car into OD you're running around 1200-1500rpms. See the difference? It's an even bigger difference at h igher speeds (3500rpms at 100-120mph in OD; 3rd gear would redline, and if capable maybe around 7-8000rpms?!?!)

Now my numbers may not be correct but you get the jist. So yeah... OD=good. Yes you'll get more power with a lower gear, but you'll be paying for it in wear 'n tear and gas milage.

[Craig99SE2]

Technically speaking, overdrive is the gear in which the transmission output shaft turns faster than the input shaft. For example, look at our 4T45E's:

1st - 2.957:1
2nd - 1.623:1
3rd - 1.000:1
4th - 0.863:1

So, in 3th gear, the input shaft (turned by engine) is spinning at the same speed as the output shaft. When you shift into overdrive, the inertial force of the car already in motion keeps it going with a smaller input load on the trans. It is specifically for saving gas when cruising by keeping engine RPM's down.

Overdrive is any gear less than 1:1 ratio.

[Craig99SE2]

Originally posted by UNC0808
how big is the difference between D and 3. i drive in D all the time. I never use 3. doesnt one of them give the car a quicker step, but also uses more gas. can someone explain the difference.

If you keep the shifter on 3, the car will shift from 1 - 2 - 3 and never go into 4th (i.e. overdrive). When in drive, it goes 1 - 2 - 3 - 4. Same as disabling overdrive in other vehicles. Unless our cars have a PCM that changes shifts according to gear selection (which I highly doubt), the transmission will shift at the same regardless of being in "3" or "D". It just won't go into 4th gear in "3" and save your gas at highway speeds.

At the dragstrip, I'd use "3" to prevent the car from jumping into overdrive at the end of the track and slowing me down.