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Unread 10-24-2013, 11:53 AM   #16
Bringbackmikey
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Ok. Dumb question from a newbie here. Trying to learn. How do I determine what I have? Feel like I have a 3.73 axle but not 100% positive.

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Unread 10-24-2013, 12:03 PM   #17
invest2m4
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Quote:
Originally Posted by Bringbackmikey
Ok. Dumb question from a newbie here. Trying to learn. How do I determine what I have? Feel like I have a 3.73 axle but not 100% positive.
Jack the front end up, give the tire a full rotation and see how many rotations the drive shaft makes. Put a chalk mark on the tire and drive shaft so you can visually keep track. Slightly more than 3 means 3.21, almost 4 means 3.73.
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Unread 10-24-2013, 12:42 PM   #18
bbbradley
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Thanks for the replies, making a change of winter DD and I was wondering what impact the 3.73 vs 3.21 would have on drivability and fuel mileage in the New England area with frequent trips to the NH/ME mountains skiing. Is it common for dealers to have multiple gearing options in their inventory for manual transmissions? I'd like to try the two back to back on whatever hills I can find in this area, sounds like highway speed hills are the challenge for the 3.21 gears. The off-road driving I would do is limited to Nantucket beaches sand driving, no heavy duty action, would that tax the engine too much too?
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Unread 10-24-2013, 12:51 PM   #19
SLADE
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Originally Posted by bbbradley View Post
sounds like highway speed hills are the challenge for the 3.21 gears. The off-road driving I would do is limited to Nantucket beaches sand driving, no heavy duty action, would that tax the engine too much too?

Sand will be enough to bog down 3.21's.

There is no benefit to 3.21's if you are not travelling at 65mph+. If your typical commute consists of slower speeds, then you will not see better MPG out of the 3.21's.


I guarantee you will not regret getting 3.73's. That can not be guaranteed with 3.21's.
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Unread 10-24-2013, 01:02 PM   #20
brianjw
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3.21s and 35s will be hell even in Illinois. At highway speed you'll be wide open trying to maintain speed. With a strong headwind? Not fun.

4 high probably won't work in sand. Not without destroying a clutch or overheating a trans.
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Unread 10-24-2013, 01:05 PM   #21
invest2m4
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The mpg difference is nominal at best. In fact, 3.21 could very well be worse if you go with a larger tire as you won't be in overdrive or 6th gear as much. I'd definitely have better mileage with 4.10 than 3.73 as I am in 5th a lot.
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Unread 10-24-2013, 01:10 PM   #22
SLADE
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Originally Posted by invest2m4 View Post
The mpg difference is nominal at best. In fact, 3.21 could very well be worse if you go with a larger tire as you won't be in overdrive or 6th gear as much. I'd definitely have better mileage with 4.10 than 3.73 as I am in 5th a lot.

MPG with 3.21's can be worse even with stock tires at less than highway speeds.
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Unread 10-24-2013, 01:12 PM   #23
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I ran 3.73's on my 13 JK 6 speed with 285's (small 33" tire), and often wished I had 4.10s.

I'm running 4.88's and 35's now and am very happy. I wouldn't want less than 4.56's with 35's.
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Unread 10-24-2013, 05:23 PM   #24
Butterjeep
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If you have money to spend on a JK, a lift, wheels, or tires you have money to regear. If you can't then you can't afford the Jeep. Would you skimp on other "extras" like gasoline, maintenance or insurance?
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Unread 10-24-2013, 07:54 PM   #25
HappyTrails
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Originally Posted by Godholio View Post
With 35s you're probably going to want to regear anyway, so the only factor in 3.21 vs 3.73 is that the 3.21 front differential is different and requires more money to regear.
This is the most important issue. The front diff is different = more $$$.
Skip the 3.21 vehicle, buy one with the 3.73's at least (at least the diff can handle deeper gears). Or just take some money saved by buying the 3.21 vehicle and swap a D44 or D60 under there.
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Unread 10-25-2013, 11:49 AM   #26
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Originally Posted by Butterjeep View Post
If you have money to spend on a JK, a lift, wheels, or tires you have money to regear. If you can't then you can't afford the Jeep. Would you skimp on other "extras" like gasoline, maintenance or insurance?
That's quite judgemental.
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Unread 10-25-2013, 12:06 PM   #27
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The truth isn't always pretty.
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Unread 10-25-2013, 12:11 PM   #28
number40Fan
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Originally Posted by invest2m4 View Post
Jack the front end up, give the tire a full rotation and see how many rotations the drive shaft makes. Put a chalk mark on the tire and drive shaft so you can visually keep track. Slightly more than 3 means 3.21, almost 4 means 3.73.
You will need to spin the tire two revolutions.
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Unread 10-25-2013, 12:41 PM   #29
Godholio
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Originally Posted by Butterjeep View Post
If you have money to spend on a JK, a lift, wheels, or tires you have money to regear. If you can't then you can't afford the Jeep. Would you skimp on other "extras" like gasoline, maintenance or insurance?
This is as asinine as people who insult others for giving a damn about mpg.
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Unread 10-25-2013, 04:10 PM   #30
NCRUBI2012
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Quote:
Originally Posted by Bringbackmikey
Ok. Dumb question from a newbie here. Trying to learn. How do I determine what I have? Feel like I have a 3.73 axle but not 100% positive.
Or call/visit local dealer. They can run build sheet for you right in the service area. Did mine today. My window sticker showed 4.10 but actually have 3.73.
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