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  #1  
Old 08-29-2010, 05:03 PM
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overdrive

I searched all over the forum and I couldn't find anything. I feel like a total noob for asking this, but, a friend asked me the other day what exactly happens when I press the button that lights up the "OD OFF" on the dash. When he asked all I could answer him with was "I have no idea."

So my question is, what does it do? I know that when I turn overdrive off, it feels way more aggressive the truck. I would really like to know when to use it and what it does.

If there's a thread already on this and I missed it, I'm sorry just set me up with a link and that would be great!

Thanks guys.
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Old 08-29-2010, 05:39 PM
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Re: overdrive

I have this exact question.
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Old 08-29-2010, 06:07 PM
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Re: overdrive

it changes the tranny from a 5 speed auto to a 4 speed auto. 5th gear is best for interstate driving etc
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Old 08-29-2010, 07:08 PM
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Re: overdrive

Actually, it changes it to a 3 speed...the 4th and 5th gears are overdrive; .75 and .67 respectively. The third gear is the standard 1:1 gearing.
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Old 08-29-2010, 08:45 PM
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Re: overdrive

So, when overdrive is off, it feels like its pulling harder because it goes through the gears faster? Also, Scott you said that having overdrive on is better for interstate driving, so should I turn it off when I'm driving around the city? Will I save fuel that way?
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Old 08-29-2010, 08:57 PM
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Re: overdrive

I was just speaking generally.....but yes...itll split the rpm's through the rpm range through the pulling gears...whatever they may be...1, 2, 3, or 4. I would leave overdrive on in city driving as itll keep the rpm's lower......as long as you dont push them higher
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Old 08-29-2010, 09:47 PM
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Re: overdrive

Alright. Thanks a lot guys. I've been wondering this for a while.
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Old 08-29-2010, 10:07 PM
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Re: overdrive

i had the same question too but i looked in my manual it gave a vague description of it but i notice it works best when im on the highway and i wanna pass sum one i turn it off and it give me better acceleration up hills but i was just worried and wondering if it would screw up my tranny
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Old 08-30-2010, 12:08 AM
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Re: overdrive

The overdrive is just there to lower the rpm, lower engine noise and safe fuel. Ofcourse with lower rpm you have less power available. On the highway even with the OD on, the tranny should shift down when you push the accelerator pedal far enough to raise the rpm and to have better passing power. The 545RFE tranny has a second 2nd gear which is used only for this reason. The first second gear is for normal acceleration.
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Old 08-30-2010, 07:03 AM
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Re: overdrive

Quote:
Originally Posted by Frango100 View Post
The overdrive is just there to lower the rpm, lower engine noise and safe fuel. Ofcourse with lower rpm you have less power available.
It's not just that the RPMs are lower so you have less power. With OD on, you have a lower gear ratio. When you push the button and turn OD off, you "lock out" (tranny won't select them) the overdrive gears (4 and 5).

With OD off, you will only have 3 gear (1, 2, and 3). The purpose is really for if you're pulling a trailer or something behind you.
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Old 08-30-2010, 11:36 AM
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Re: overdrive

Quote:
Originally Posted by Frango100 View Post
...The 545RFE tranny has a second 2nd gear which is used only for this reason....
The other 2nd gear is for the downshift, that allows better braking force from the engine. It is not engaged on upshifts.
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Old 08-30-2010, 11:42 AM
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Re: overdrive

The jeep service manual says the following regarding the secondary 2nd:

The alternate second gear ratio (2prime) allows
smoother 4-2 kickdowns at high speeds to provide
2nd gear passing performance over a wider highway
cruising range.
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