What is Overdrive anyway

[coopns]

Sorry for the awful question. Driving the 02 Camry and never really thought too much about the O/D button.

Should it be on (which it is)?

What does it do and does it effect milage?

 

[beast3300]

Leave overdrive on at all times. It means in top gear (4th or 5th depending on your transmission) that the transmission will spin faster than the engine (engine rpms) which improves fuel economy.


edit: Not at all times but, it can help with engine braking like a long downhill scenario. And can help during towing situations.

Just to name a few.

 

[kevinf]

The button turns the overdrive off, (a dashboard light goes on when it's off). Turning the overdrive off replaces the old D-3 position, best used if you find the transmission "hunting" for the proper gear if you're ascending a shallow slope and need a bit of oomph. In other words, it's very nearly useless.

 

[crinkles]

I use it "off" to engine brake all the time.

 

[Spazdog]

99.9% of the time, just select Drive and go.

If you are carrying a heavy load through hills and your transmission is hunting between 3rd and 4th gears you might consider turning the overdrive off.

A lot of cars don't even give you the option. The older Ford Fusions just had Park, Reverse Neutral and Don't even think of selecting your own gear.
There was also an "L" but it did not hold the car in low gear. or 2nd for that matter.

 

[hate2work]

Originally Posted By: beast3300
And can help during towing situations.


Never tow in overdrive, quickest way to ruin a tranny.

 

[whip]

Originally Posted By: crinkles
I use it "off" to engine brake all the time.

Unless you live in a hilly area, you should use the brakes to slow the car. Using the engine will accelerate wear on the C/V joints.

 

[beast3300]

Originally Posted By: hate2work
Originally Posted By: beast3300
And can help during towing situations.


Never tow in overdrive, quickest way to ruin a tranny.


Or race a 4T65 (HD or not) in Overdrive. When you let off, it will slam into OD which is similar to Styrofoam in GM's 4T65.

 

[oggb]

Originally Posted By: beast3300
it will slam into OD which is similar to Styrofoam in GM's 4T65.


Got a good laugh out of that.

 

[LargeCarManX2]

A ratio lower than 1to1.

 

[Calonzap]

Don't make a mountain out of a molehill. Turn the O/D button ON and leave it alone. Most automatic transmissions do a better job of shifting than most drivers, anyway. If you're advanced enough to be pulling a trailer, you should already know what you're doing and shouldn't have to ask anyone's advice.

 

[eljefino]

My non-overdrive "drive" position does not engine brake; whatever clutches etc are involved make it basically neutral.

Manual 2nd and 1st, however, do slow things down.

 

[sciphi]

It's letting the transmission go into top gear.

Sometimes I'll manually shift my 4T65 into "drive" going up a long, steep hill around 45 mph. It keeps it from dropping speed too much.

 

[goodtimes]

Generally it means a ratio less than one, engine/trans rpm. My Chrysler has a 4th speed overdrive ratio of .69, so 690 engine rpm gives 1000 rpm at the trans output shaft. The axle ratio is 3.45, the ratio of trans rpm to wheel rpm. The final ratio is (.69)x(3.45)= 2.38 in OD. Saves gas and engine wear. Owners and service manuals can have the ratios for the gears, if one is interested in such things.

There is also lockup in the higher gears, which means the trans stops slipping through the torque converter, essentially becoming solid drive like a manual shift trans. That increases mileage as well. Watching the tach, at times, you can see these effects as they work.

 

[The motor guy]

Just make sure that if you turn overdrive off to give you more rpm to make sure the torque converter locks. I used to have a ford ranger and I always turned the overdrive off but about a year or so after I sold it I realized i probably did mor harm than good because I don't think the the torque converter locked up. Apparantly it's really supposed to be used to keep the torque from locking and unlocking and also shifting between gears. say constantly from 4-5 and back. But I only towed like 3 or 4 miles so it probably wasn't far enough to get the fluid cooking enough and overheat. The truck I have now allows you to control all 6 gears if you want and also has tow/haul mode which locks up the converter on all gears all the way down to like 2 or third gear.

 

[beast3300]

Originally Posted By: JRed
Originally Posted By: beast3300
it will slam into OD which is similar to Styrofoam in GM's 4T65.


Got a good laugh out of that.



It's true, OD is straight junk in it.

 

[mechtech2]

Overdrive came from putting a unit in series on a regular transmission -it was on the rear as an added device. In high gear, transmissions were straight through - one to one input to output. An overdrive unit made it so the engine spin slower for the same output speed [road speed, too].

Now overdrive is a much more vague term. it implies a lower engine speed for the same road speed. [This is a good thing for cruising.] Now this is usually done internally in the tranny.

Normally leave it on.
Disregard anyone's advice to use it for extra braking. It works in the OPPOSITE manner for this!

 

[asiancivicmaniac]

My car only has 1,2,D3,D4,N,R, and P. I assume D4 is O/D.

 

[mechanicx]

A lot of transmission will still give engine braking (not go into neutral)when coasting while in OD if vehicle speed is over ~50 mph. Also they will unlock the converter while in OD if the accelerator is pressed more than about half way for more power. At lower speeds under 50 mph some transmission will go into nuetral when coasting when placed in Drive. But if you place the shifter into manual 3, 2 or 1, you get engine braking and no converter lock up. At least that is the typical strategy on most GM 4 speed automatics.

 

[crinkles]

I can tell you mine DOES engine brake with O/D off. and owner's manual recommends it for hilly driving etc.