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Old 12-28-2013, 02:15 PM   #1
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Looking for the hard-to-find answers

So I'm new to this JK world having just gotten rid of my TJ. My new jeep is a 2007 with D30/D44 with 3.21 gears and is completely stock (minus the audio setup). I really want to get a little 2.5" lift and run 35's but theres is no possible way for me to rehear for probably 8 years once i get out of high school and start my career, heck it's hard enough paying for the Jeep and gas while in high school. Ive searched the inter web many many times and can't find any real world experience of running 35s with 3.21s and the 3.8l and an automatic transmission. Living in the south my playground is mud, and thats on very rare occasions. For now this will mostly be a mall crawler.

The questions:
Gas mileage?
Mechanical wear?
Driving at 70mph (occasionally)?
Driving at 60mph (very often)?

Thanks!

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Old 12-28-2013, 02:48 PM   #2
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Your gas mileage will completely suck.

You will increase mechanical wear and tear.

Your Jeep will still go 70mph and it will obviously go 60mph. I don't understand the point of those questions.

It will feel like a complete slug with those gears and that automatic transmission.

To say those answers were hard to find, simply means you didn't read very much on this forum.

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Old 12-28-2013, 07:45 PM   #3
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Estimates on mileage: 10city 12-14 highway. You have a manual right? I don't think they had 3.21 with an auto in '07 did they? If its a manual it'll put more wear and tear on your clutch. If you can get a super light setup maybe it could be bearable. The only super light 35" I know of is a 35/12.5/15 BFG AT and a 15" alloy. It's only a few pounds heavier than the 33" duratrac combo everyone likes to run so with that your mileage won't be nearly as bad. Most 315/xx/xx tires are D or E range and will be much heavier than the combo I stated above

If you don't get 35's you could always do a 33/12.5/15 and that would be a little better mileage. That may be 15 and 17mpg give or take a bit
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Old 12-28-2013, 07:48 PM   #4
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He definitely said that he has an automatic transmission. The truth of the matter is that he has no clue because 07 automatic transmissions had 4.10's.
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Old 12-28-2013, 08:27 PM   #5
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He definitely said that he has an automatic transmission. The truth of the matter is that he has no clue because 07 automatic transmissions had 4.10's.
07 Rubicons with an auto tranny had 4.10's. He didn't buy a Rubicon.
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Old 12-28-2013, 08:34 PM   #6
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07 Rubicons with an auto tranny had 4.10's. He didn't buy a Rubicon.
2007 Auto X,Sahara and Rubi has 4.10 gears
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Old 12-28-2013, 08:37 PM   #7
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If you get some 315-7X-XX tires you should be ok. They usually measure 34.5" or go with 33's for best performance.
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Old 12-28-2013, 08:37 PM   #8
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Originally Posted by Spencer11496 View Post
So I'm new to this JK world having just gotten rid of my TJ. My new jeep is a 2007 with D30/D44 with 3.21 gears and is completely stock (minus the audio setup). I really want to get a little 2.5" lift and run 35's but theres is no possible way for me to rehear for probably 8 years once i get out of high school and start my career, heck it's hard enough paying for the Jeep and gas while in high school. Ive searched the inter web many many times and can't find any real world experience of running 35s with 3.21s and the 3.8l and an automatic transmission. Living in the south my playground is mud, and thats on very rare occasions. For now this will mostly be a mall crawler.

The questions:
Gas mileage?
Mechanical wear?
Driving at 70mph (occasionally)?
Driving at 60mph (very often)?

Thanks!
What version JK did you get? Not that it really matters but to clear up the questions below seems like you probably have 3.73's or 4.10's but then again could be 3.21's. Your gas mileage won't change much maybe 1mpg or so less with 35's. It will not be great at elevation but will get to speed on the HWY. technically yes bigger tires and lift will wear on your driveline more than stock. Lifts will require more maintenance than stock so if money is a concern I would leave it stock until you have more money. Just my .02
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Old 12-28-2013, 08:38 PM   #9
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2007 Auto X,Sahara and Rubi has 4.10 gears
Not all.. When I purchased my 07 that was not the case.
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Old 12-28-2013, 08:41 PM   #10
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Hmm I wasn't aware of this 4:10 thing. Are we sure here ?

OP ... Request a build sheet.
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Old 12-28-2013, 08:45 PM   #11
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My $.02.

I know it's not what you want to hear. But, if budget is a serious issue for you, as it is for most high schoolers. I would recommend that you enjoy your je as is. Take the top off and get some cheerleaders to ride around with you. Your jeep doesn't have to be a rock crawler to be a jeep. Have fun. Enjoy your awesome ride.
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Old 12-28-2013, 08:46 PM   #12
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Not all.. When I purchased my 07 that was not the case.
You might want to take another look.
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Old 12-28-2013, 08:47 PM   #13
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Hmm I wasn't aware of this 4:10 thing. Are we sure here ?

OP ... Request a build sheet.
Damn newbies! The X also had optional lockers.
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Old 12-28-2013, 08:49 PM   #14
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Well looks like I'm going to sleep tonight with new knowledge
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Old 12-29-2013, 01:51 PM   #15
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What version JK did you get? Not that it really matters but to clear up the questions below seems like you probably have 3.73's or 4.10's but then again could be 3.21's. Your gas mileage won't change much maybe 1mpg or so less with 35's. It will not be great at elevation but will get to speed on the HWY. technically yes bigger tires and lift will wear on your driveline more than stock. Lifts will require more maintenance than stock so if money is a concern I would leave it stock until you have more money. Just my .02
Its the X and according to the tag on my pumpkin its a 3.21, well thats what it looks like it says. It doesn't feel like 3.73 like my TJ had. And you say mpg will only drop 1 or 2, is that with 4.10 or 3.21?
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Old 12-29-2013, 01:55 PM   #16
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Originally Posted by daggo66 View Post
Your gas mileage will completely suck.

You will increase mechanical wear and tear.

Your Jeep will still go 70mph and it will obviously go 60mph. I don't understand the point of those questions.

It will feel like a complete slug with those gears and that automatic transmission.

To say those answers were hard to find, simply means you didn't read very much on this forum.
The questions about the speed I should have been more specific on: What will it be like driving at 70 mph? RPMs? Strain on the engine? Gas mileage?

Could you perhaps tell me where to find my actual gear ratio? Like I said Im new to the world of JK's, I'm still use to all the TJ stuff.
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Old 12-29-2013, 02:06 PM   #17
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You might want to take another look.
I had 4.10's but I also had a Rubicon and I also have helped friends with axle issues on 07's I am certain that they didn't all come with 4.10's. But you can think what you want I am sure nothing I say is going to change your mind. Not to mention the tag the OP is referencing that tells him what gear set he has.
I have also had 8 JK's since then and I have had all the diffs open other then the current one I have now which has 4.10's but it was an added option on this Rubicon.
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Old 12-29-2013, 02:11 PM   #18
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My $.02.

I know it's not what you want to hear. But, if budget is a serious issue for you, as it is for most high schoolers. I would recommend that you enjoy your je as is. Take the top off and get some cheerleaders to ride around with you. Your jeep doesn't have to be a rock crawler to be a jeep. Have fun. Enjoy your awesome ride.
Agreed with above... If budget is an issue enjoy the jeep the way it is stock and mod in the future when you have more money for mods and maintenance.
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Old 12-29-2013, 02:20 PM   #19
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OP the easiest way to verify gear ratio is to jack up one rear wheel and put your tranny or transfer case into neutral. Obviously block the front tires to keep your Jeep from rolling. Put a mark on the drive-shaft that you can see. Spin the tire by hand one revolution while watching the drive-shaft. If the drive-shaft spins a little more than three times you have 3.21 gears. If the drive-shaft spins almost 4 times, you have 3.73 gears. If the drive-shaft spins a little more than 4 times, you have 4.10 gears.
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Old 12-29-2013, 02:37 PM   #20
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OP the easiest way to verify gear ratio is to jack up one rear wheel and put your tranny or transfer case into neutral. Obviously block the front tires to keep your Jeep from rolling. Put a mark on the drive-shaft that you can see. Spin the tire by hand one revolution while watching the drive-shaft. If the drive-shaft spins a little more than three times you have 3.21 gears. If the drive-shaft spins almost 4 times, you have 3.73 gears. If the drive-shaft spins a little more than 4 times, you have 4.10 gears.
There you go
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Old 12-29-2013, 02:39 PM   #21
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OP the easiest way to verify gear ratio is to jack up one rear wheel and put your tranny or transfer case into neutral. Obviously block the front tires to keep your Jeep from rolling. Put a mark on the drive-shaft that you can see. Spin the tire by hand one revolution while watching the drive-shaft. If the drive-shaft spins a little more than three times you have 3.21 gears. If the drive-shaft spins almost 4 times, you have 3.73 gears. If the drive-shaft spins a little more than 4 times, you have 4.10 gears.
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Old 12-29-2013, 05:32 PM   #22
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Exactly...well said. Sometimes all the details we get caught up in negate the reason we all bought Jeeps in the first place.

Quote:
Originally Posted by Matthew_JK View Post
My $.02.

I know it's not what you want to hear. But, if budget is a serious issue for you, as it is for most high schoolers. I would recommend that you enjoy your je as is. Take the top off and get some cheerleaders to ride around with you. Your jeep doesn't have to be a rock crawler to be a jeep. Have fun. Enjoy your awesome ride.

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