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Hi

I'm lifting my JK Unlimited 2008 with a 5'' L.A. and putting 37 '' tires under it.

According to the new gear ratio formula on the following link

http://www.4x4offroads.com/gear-ratio-chart.html

The perfect gear for 37'' would be 4.74

So 4.88 beeing a little bit sronger, would be the logical choice, but you guys with 37'' always have 5.13 gears.

Any reasons that I should know before I make my choice.

Thank's
 

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Automatic?

Whether standard or auto, since it's an Unlimited with 37's, you will be happier going to a 5:13. I have seen the superior 5:13 next to the OEM 4:10 pinion and the size difference is not enough to avoid the 5:13. I would choose the 5:13 over the 4:88 for your application, especially if you have an automatic.
 

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Yeah I would stay away from 4.88's and 37's you will be much happier with the 5.13's or 5.38's. I just did my gears and at the last minute swapped the 4.88's I bought for 5.13's and I am glad I did.
 

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5.38s...:D Thats whay I am putting in with my 40s...:thefinger:
 

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I am running 35's, and when I went to change my gears the charts said 4.56's would be the return to stock ratio. I went with 4.88's and I like them alot. So going up a ratio seems to be the ticket.:bounce:
 

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I'd recommend 4.88's for 37's on the JK if you are running a manual tranny.
I'd say the additional strength of the pinion head outweighs the very slight "performance" gain, not to mention, that higher rpm burning more fuel. The pitiful performance that the 3.8 mill provides at any rpm can not be compensated for by gearing. With 4.88's or 5.13's, you won't get what you really want....so go for strength and fuel economy.
Check this out: http://jeep.off-road.com/jeep/Edito...Article/detail/571473?contextCategoryId=32444

I have 4.88's, manual tranny and 37's
My buddy has 5.13's, auto tranny and 37's

Mine feels more "powerful", with more torque, and is better suited to the big rocks...mostly due to the transmission. Mine is better around town and on the highway. It also get 1.5mph better on average. His still downshifts on highway grades and never seems controlled, even with the 5.13's.
 

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So

5.13 seems to be almost unanimous.

By the way my rubicon is a manuel.

Any other comments of people that have a 4.88 with a manual.
The last comment I'll make is this:
While the difference in size and strength of an aftermarket 4.88 and 5.13 is not that much, I did speak with a manufacturer of JK specific gears about pros and cons to each. They were able to report that in more than a few cases of moderate to extreme use, the 5.13s showed some breakage, while the 4.88's have seen none to date. Could this have been coincidental or just a weak spot in the materials used? Maybe. Personally, I would never use anything lower than a 4.88 in a Dana 44. Keep in mind the mating surface of the gears as the torsional flex and spreading that happens to a gear case and the axle housing around it. The smaller you make that pinion head, the less surface contact for the gears. This is the reason for chipped and broken teeth....and why people truss their axle housings and use super strong diff covers. Not trying to be unreasonably biased or trying to scare anyone...just giving facts that I know of. I would guess that 95% of the guys on this board will never push their JK's to the limits of any kind of breakage...so I'd say that going with 5.13's is a safe route.
 
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I have 5.13's with an auto (37's) and it is fine, I wish i had 5.38's but they were not available, go with the lower gearing, you wont regret it.
I’d have gone with 5.38 had they been available also but 5.13 are working well.
 

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4.88 FINE IF YOU GOTTA STICK AUO GO 5.13. BUT EITHER WAY FOR A FEW MORE BUCKS AND JUST GO W/ THE 5.13'S AND I THINK YOU WILL HAPPY AS HAPPY CAN BE
 

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I am putting in the 5.13's. And I have the d-30 up front. Superior will warranty breakage of the gears for 2 years and lifetime on the axle shafts. I would think we'll see 5.38 options for the D-44 at some point. They are available for older D-44's.

If you have a Rubi w/ lockers... make sure you call Superior direct and tell them the year of the JK. There are 2 different Ring gear-carrier bolt sizes. They have a kit to adapt if you have the new size. I think it's only the '09s with the issue.
 

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well... don't that beat the dog... My 5.13's came in Friday. And now they are releasing 5.38's for the D-44's.
 
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