Overdrive in A/T..Turned Off..Benefits..?

[solaris=amazing]

Hey guys, i have a 95 tbird with a 4 speed overdrive a/t. Under 65mph, i usually keep overdrive OFF because i hate how when IN overdrive, the a/t keeps trying shift at cruising speeds....plus leaving o/d off gives my car more power...well, better shifting.. At 65mph+ i turn her on to save gas, cause at those speeds, going from od off to od on drops the rpms by atleast 1000rpms.

Now, i've read that keeping od off burns more gas, but is infact better for the a/t cause it creates less heat...because of less shifting...that true..? Also, will the extra rpms at higher speeds kill the engine faster... Lastnight i wanted to see how this car felt with only 3 gears instead of od's 4 gears, and believe it or not it felt much more punchy and faster at 85+...BUT the engine runs a good 1000rpms faster.

Another thing, when you take off overdrive..and have only 3 gears, does those 3 gears become wider...? Or is it just basically taking out the 4th overdrive gear..?

[curtis73]

Originally Posted by solaris=amazing

Hey guys, i have a 95 tbird with a 4 speed overdrive a/t. Under 65mph, i usually keep overdrive OFF because i hate how when IN overdrive, the a/t keeps trying shift at cruising speeds....plus leaving o/d off gives my car more power...well, better shifting.. At 65mph+ i turn her on to save gas, cause at those speeds, going from od off to od on drops the rpms by atleast 1000rpms. Now, i've read that keeping od off burns more gas, but is infact better for the a/t cause it creates less heat...because of less shifting...that true..? Also, will the extra rpms at higher speeds kill the engine faster...

You are wise to keep your tranny out of OD if its shifting. The A/T uses friction clutches to "gradually" apply gears without the need for an actual clutch pedal. Several other things are different, but the extra shifting does wear on the clutches and create heat. The worn-off clutch material also goes into the tranny fluid. Its not a huge concern, since it happens anyway, but anything you can do to lessen it will help the tranny last longer.

It will probably burn more gas, but do a test. Run a tank on the highway in OD and run a tank without OD and see what kind of mileage difference you get. Depending on several factors including gear ratios, transmission shift points, and engine parameters, dropping the RPMs is not always going to save gas. If the tranny keeps shifting in and out of OD at 65, my guess is that its not going to save much gas.

Its also possible (since you have an AOD tranny in that car) that its not actually shifting. Without getting too technical, the torque converter has a lockup function. Often times on the highway it will lock and unlock without the tranny actually shifting gears. A good way to tell is to do this: When you're on the highway and you feel it "shift" down, manually take the tranny out of OD. If it downshifts again, you know it was just the torque converter unlocking. If it doesn't, then you know the tranny has already shifted on its own. If its just the torque converter, there's not much you can do about it. Sometimes they wear and let themselves lock and unlock too frequently and replacing it with a new one will prevent that from happening as often. The computer tells it to lock and unlock, so it will still happen but not as frequently since it won't be doing it on its own.

If you ever notice a shudder or vibration as it shifts into OD on those fords its the torque converter. It almost feels like you're running over a little rumble strip in the pavement. If they get bad enough to start vibrating like that I suggest replacing them, but until that point just put up with the frequent lock/unlock.

Lastnight i wanted to see how this car felt with only 3 gears instead of od's 4 gears, and believe it or not it felt much more punchy and faster at 85+...BUT the engine runs a good 1000rpms faster.
Another thing, when you take off overdrive..and have only 3 gears, does those 3 gears become wider...? Or is it just basically taking out the 4th overdrive gear..?

Yep, its punchy alright. I love that feeling too. Leaving OD off is just like leaving a four speed manual in third gear. It doesn't change the shift points or gear ratios of the other three gears, it just holds it out of fourth. Its punchy because you're engine is revving up where it makes more power. The higher RPMS don't hurt things to an extent. Revving it to redline is fine during acceleration, but for long-term highway travel, I say keep it under 3000 rpms. Any more than that and you're just wasting energy and causing excess wear.

[solaris=amazing]

Jeez, thanks curtis, you always explain things in great detail..

As far as the torque convertor, you are correct. About 5 months ago, my car was shuddering at 30-35 and at 60-65. I had my mechanic check out the tranny, and it turned out to be the fluid.. He said the tc was fine...everything alittle worn (stock tranny/127k miles), but as far as how this held up..VERY GOOD.

Thank god the owner before me changed his tranny fluid every 25/35k miles. Now i get NO shuddering, and thats an INFAMOUS problem with this tranny's.

Man this thread..and your reply makes me want a M/T so much more.. Lol, i will test that out (gas mileage on highway). I knew i was helping my tranny a tad by leaving it off o/d, plus, when you got your car packed with 4 people (roughly 600+lbs) the last thing you want is a shift happy overdrive. With o/d off, i notice a MAJOR differance...especially when you have the a/c on in the summer-and it kinda makes your car a hair bit slower, you don't notice it with o/d off.