So, I have an Auto transmission in my car, and on the side of the shifter, there is a button that turns of the overdrive. My question is, why would I want to do that? What purpose would be served by disabling my overdrive?
In general driving, you wouldn’t. All it does is turn your four speed into a three speed, or your five speed into a four. Agreed, it’s sensible to leave it on for most of your suburban driving.
It might be desirable to disable it if you are descending a very long grade, or if you are doing some heavy towing.
Disabling overdrive keeps the transmission from “hunting” - a condition where it can’t decide what gear to be in and keeps shifting back and forth.
This link describes the condition.
I did not look at the link but I thought I would add my own 2 cents. The Overdrive “Off” button can sometimes be called a “Manual” Shift button. It gives the driver total control over shifting without a clutch and it can be alot of fun for people who like to drive wild. Of course this is my personal experience with limited vehicles so I would say the link would probably be a better source.
nodope, that’d work for driving a “virtual manual” as far as holding lower gears longer for upshifting goes, but in the vast majority of auto boxes, you won’t be able to hold higher gears longer than the auto dictates when you slow down.
I saw this in my friend’s & I opened the glove compartment & read the manual on it. The manual was pretty informative & discusses how it makes it easier for the car to decide to shift, as mentioned above, assuming you have the same car as she does.
Sounds like a Toyota. My RV has this setup and I usually leave OD on unless climbing hills. The 4th gear will normally allow for better gas mileage on the long haul, but in town may be nominal.
Basically, turn it off if you’re in a hurry.
My little Mazda has this and I love it in the slushy Canadian wintertime. On mornings where there was deep slush and very little traction, I clicked the little button and just did the slow and steady crawl to work. I didn’t get there quick, but many other people didn’t get there at all!
Every 4-speed/overdrive automatic transmission allows the driver to eliminate 4th (overdrive) gear. On some this is done with a button or switch, on others it is done with a shift lever position (D4-D3-etc. or OD-D-etc.).
One reason to de-select 4th gear has been mentioned, to eliminate hunting. I find hunting most common in hilly or mountainous terrain, going uphill. There’s not quite enough oomph in 4th, so you press the accelerator a bit more and it downshifts into 3rd. Then you’re accelerating too briskly so you let up on the accelerator and it upshifts into 4th. Back and forth. Over and over. You eliminate this annoyance by hitting the button or moving the shift lever so that it won’t shift into 4th. The tranny then acts like a 3-speed automatic.
Another reason is to get some engine braking effect on long downhill grades.
A third situation that applies to a least some cars is trailer towing. Some automatics operate such that when taking off from a standstill, during which the car is in 1st gear until it shifts, the internal power path is sturdier in drive than it is in overdrive. With these designs, it is wise to select drive when pulling a heavy load.
dutchboy208, that doesn’t make sense. The acceleration is not affected by eliminating 4th.
eveayn, you’re apparently confusing Mazda’s “hold” button with the “overdrive off” button some other cars have. It’s a whole different animal.
In addtion to the information above, I have also heard it recommended for stop-and-go traffic. Apparently the constant shifting of gears can be hard on the transmission and prohibiting use of the top gear or two will prevent excessive shifting. I equate that information with “OD is primarily for the open road” and I keep mine off in the city and during the rush hour commutes.
Not only does it disable OD, but (at least in my car) it also moves up the shift points for 1->2 and 2->3