Overdrive off with stock gears?
Thread Starter
JK Freak
Joined: Jul 2010
Posts: 538
Likes: 1
From: CAMP LEJEUNE, NC
Overdrive off with stock gears?
so i have two posts already where they say something like "just turn your overdrive off if you have 3.73 and an automatic and larger tires" well its not excactlly worded that way lol but can someone explain to me why people say that or what the advantages are. i feel like im missing something.
JK Junkie
Joined: Nov 2008
Posts: 3,297
Likes: 8
From: Cabot, Ar.
Your OD is your top gear. With oversized tires ( or towing a heavy load ) your transmission will not be able to stay in the higher gear. Sometimes it will actually shift back and forth trying to stay in the higher gear. This is hard on the engine and the transmission. 
JK Junkie
Joined: Nov 2008
Posts: 3,297
Likes: 8
From: Cabot, Ar.
If were me, I'd only turn it off when my tranny started having a hard time keeping up. You might be fine in some situations with OD on. Your going to be burning more gas if tranny wants OD but you have it turned off. Just keep an eye out for when the tranny starts to downshift often.
JK Jedi Master
Joined: Jan 2008
Posts: 11,463
Likes: 165
From: Austin <--> Colorado Springs
OD Off forces the transmission to NOT use OD (4th gear).
It may be easier to think about it using some numbers...
You have an auto with 3.73's and 37's? Measure the tires and plug some numbers into the chart in the drivetrain faqs to get the OD On rpms. To get OD Off, divide that number by .69. (these examples are assuming a 36" actual height on the 37s).
3.73, 36" actual, (OD On)
1682 rpm @ 70
3.73, 36" actual, (OD Off)
1682 / .69 =
2437 rpm @ 70
Then compare those numbers to a new gear set.
4.88, 36" actual, (OD On)
2201 rpm @ 70
5.13, 36" actual, (OD On)
2313 rpm @ 70
5.38, 36" actual, (OD On)
2426 rpm @ 70
You'll notice that your current setup, with OD Off is very, very close to 5.38's with OD On. Correct?
This does not help you with low end grunt, and you might find that it sucks offroad, but pushing the OD button will make freeway driving acceptable until you get around to regearing.
It may be easier to think about it using some numbers...
You have an auto with 3.73's and 37's? Measure the tires and plug some numbers into the chart in the drivetrain faqs to get the OD On rpms. To get OD Off, divide that number by .69. (these examples are assuming a 36" actual height on the 37s).
3.73, 36" actual, (OD On)
1682 rpm @ 70
3.73, 36" actual, (OD Off)
1682 / .69 =
2437 rpm @ 70
Then compare those numbers to a new gear set.
4.88, 36" actual, (OD On)
2201 rpm @ 70
5.13, 36" actual, (OD On)
2313 rpm @ 70
5.38, 36" actual, (OD On)
2426 rpm @ 70
You'll notice that your current setup, with OD Off is very, very close to 5.38's with OD On. Correct?
This does not help you with low end grunt, and you might find that it sucks offroad, but pushing the OD button will make freeway driving acceptable until you get around to regearing.
Super Moderator
Joined: Jun 2011
Posts: 11,054
Likes: 85
From: Hendersonville, Tennessee
Originally Posted by profebill
I turn off my od when i need to pass on the highway and leave it off around town. 35's & 3.73 auto