Best to keep it on or off?

 

Most choose to keep it on, or not have the OD=OFF light on. The reason being is in a 1/4 mile, there's just enough room for the overdrive gear to give it a little extra juice. If you're not racing a full 1/4 mile, then you'll probably want to turn it off--this way you car stays accelerating in 3rd gear, giving the most horsepower to your wheels in that shorter amount of time--OD would probably hurt your total time.

 

So how exactly does it affect the third gear, and y do my rpms jump when I drive in second and turn off the overdrive?

 

under WOT, the car locks the torque converter and since overdrive is not actually another gear (read up on it on howthingswork.com) the car wont shift into "4th" during a 1/4, or probly even a 1 mile race for that matter. If you run the quarter mile and try turning OD on then off and back and forth as you're drivin, there will be no difference in the times, since the overdrive does not change gearing, increase power, etc. sorry guys

 

that clears that misconception up. so od off = stretch out third gear, avoids going into a cruise gear - 4th in Autos.

 

Actually the car will shift into 4th in the 1/4, mine does it all the time. It does change the gearing. All you have to do is hit redline in 3rd while O/D is on and it shifts. Mind you, your car has to be fairly fast for this to happen. My speedo is hitting around 125 MPH when it shifts even though I am just over 100 MPH because of the size of my front tires. (22")

If I didn't shift into 4th or O/D my engine would be bouncing off the rev limiter before the end of the 1/4.

 

Jime - you might be the exception I only trap around 95, and since I dont have smaller wheels for the strip, my speedo only reads 95, so i'm right in the middle of 3rd. So leaving OD on wouldnt make a difference. But I trust the opinion of you more than myself, a college kid. By leaving OD off, you're saying the gearing for 3rd is different than when OD is on? I've never noticed any difference in RPMs when i'm in 3rd vs Drive...

 

You are correct is saying that there will be no difference in times with O/D on or off. 3rd is is 3rd gear, the ratio is the same no matter what we do.

But the car will shift into 4th in the 1/4 you just have to be going fast enough and 4th is actually another gear. When I said it changes the gearing, I mean when it shifts from 3rd to 4th. Not sure what you mean by saying that 4th is not actually another gear.

 

Hmm... its been a while since i've looked at how the auto tranny really works. I must have misunderstood the articles I read a few years ago... overdrive is another gear like you said. sorry for the mis-information. I think I misunderstood my readings in that the overdrive causes faster output speed than input speed, the opposite of a gear reduction which 1st-3rd do, at least for our trannys. Somehow I misread that as overdrive being like a variation of 3rd gear??? Not sure. Anyways, yes, 4th is another gear, as you said. Ha I doubt my car will ever be fast enoguh to shift into 4th gear/overdrive in the 1/4! But thats ok...

 

Just to help ... Torque convertor lock up and overdrive are two different things. "Lock up" is when the torque convertor is mechanically "locked" and allows no slipage/torque multiplication. This is more effecient when cruising on the highway because the torque convertor is not slipping/stalling and transferring all power to the wheels and also lowers cruising rpm's. Lock up can be helpful at the top end of the 1/4 mile also, if the trans. can handle it. Overdrive is actually a gear... and in our case (auto's) 4th. In a 5 speed Maxima it would be 5th. I know on a 6 speed Vette/Camaro/Firebird, 5th and 6th are both overdrives.

Just sharing good news,
Gears

 

Hopefully I will be into 4th tonight at the strip