Axle ratios
04-01-2008, 08:17 AM
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Axle ratios
I am new to Jeepin'! (Wish i had got one YEARS AGO!!!!) I have been a ford man, and all my trucks and such i have had, have a tag bolted on the diff covers that state the axle ratio. I do not see one on the JK. I bought it used and I would like to know what gears I have. It is not a Rubi and I know i dont have 4.10s but I dont know if I have 3.73s or 3.21s. I think i have 3.21s
but I am wondering how to find out with out taking the thing apart! BTW, I have the 6 speed manual, and I average between 18 and 20 mpg depending on how and where I drive. If i go to 35s what ratio should I go to for resonable milage but still have enough umph to four wheel, 4.88s or 5.13s? Thanks ahead of time.
but I am wondering how to find out with out taking the thing apart! BTW, I have the 6 speed manual, and I average between 18 and 20 mpg depending on how and where I drive. If i go to 35s what ratio should I go to for resonable milage but still have enough umph to four wheel, 4.88s or 5.13s? Thanks ahead of time.
04-01-2008, 10:27 AM
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I am new to Jeepin'! (Wish i had got one YEARS AGO!!!!) I have been a ford man, and all my trucks and such i have had, have a tag bolted on the diff covers that state the axle ratio. I do not see one on the JK. I bought it used and I would like to know what gears I have. It is not a Rubi and I know i dont have 4.10s but I dont know if I have 3.73s or 3.21s. I think i have 3.21s but I am wondering how to find out with out taking the thing apart! BTW, I have the 6 speed manual, and I average between 18 and 20 mpg depending on how and where I drive. If i go to 35s what ratio should I go to for resonable milage but still have enough umph to four wheel, 4.88s or 5.13s? Thanks ahead of time.
but I am wondering how to find out with out taking the thing apart! BTW, I have the 6 speed manual, and I average between 18 and 20 mpg depending on how and where I drive. If i go to 35s what ratio should I go to for resonable milage but still have enough umph to four wheel, 4.88s or 5.13s? Thanks ahead of time.I can say you definitely don't have the 3.73's, they are only in the 2008 models. 2007 had 3.21's or 4.10's (Rubicon, all auto's, tow package, or upgrade for $50). Looking at the options you have no indicators of 4.10's, but maybe they checked the $50 gear upgrade option. If you go to 35's you would likely want to regear no matter what, so it might not matter much.
04-01-2008, 11:42 AM
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haha, i'm actually changing my diff fluid now! 
anywho, do you have a 2" receiver hook on the rear? if it's mopar then there is a good sign that you have the tow-package which means you also have 4.10s (like me).
i think there are a few sites on the net to tell ya too!
anywho, do you have a 2" receiver hook on the rear? if it's mopar then there is a good sign that you have the tow-package which means you also have 4.10s (like me).
i think there are a few sites on the net to tell ya too!
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04-01-2008, 06:15 PM
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Do a search, there was a prior thread regarding this and I don't remember exactly how to do this, even though I used to do it a century ago as a kid.
Jack up the entire rear end. Both wheels off the ground. Chock the front wheels, put the tranny in nuetral. Chalk a matching line between the drive shaft and the pumpkin. Chalk a line on the wheel with a matching one on the ground.
Spin a wheel and count the revolutions of the drive shaft. Maybe count two or three times in a row like this, one full spin of the wheel count how many times the drive shaft turned, repeat to be sure and you should be able to calc the ratio.
At one time I remember chalking the inside of the wheel and getting under the vehicle and watch the driveshaft mark and turn the drive shaft counting until the wheel made one full revolution. 3.73 revs to one wheel and voila! And yes, I believe Jeeps in 07 had 3.21, 3.73, and 4.10. I thought they were included on the sticker on the door, but I'd have to look and I'm too lazy ATM.
Jack up the entire rear end. Both wheels off the ground. Chock the front wheels, put the tranny in nuetral. Chalk a matching line between the drive shaft and the pumpkin. Chalk a line on the wheel with a matching one on the ground.
Spin a wheel and count the revolutions of the drive shaft. Maybe count two or three times in a row like this, one full spin of the wheel count how many times the drive shaft turned, repeat to be sure and you should be able to calc the ratio.
At one time I remember chalking the inside of the wheel and getting under the vehicle and watch the driveshaft mark and turn the drive shaft counting until the wheel made one full revolution. 3.73 revs to one wheel and voila! And yes, I believe Jeeps in 07 had 3.21, 3.73, and 4.10. I thought they were included on the sticker on the door, but I'd have to look and I'm too lazy ATM.