Axle Gear Ratio Options

[rplowden]

Need some advice. Recently bought a 2007 JKU. It is completely stock with 3.21 gears. This isn't going to work. The plan is 2.5"-3.0" lift with 35" tires and the ability to tow a teardrop trailer with gear and 5 people. Looks like the two best options will be 4.10 or 4.56 gears. Anyone have similar setups that can share thoughts?

Also, will plan to do lockers while I'm at it. I haven't done any research here yet, but if you have suggestions, my ears are open. I prefer simple and failproof to more complex/fancy options. Thanks!

 

[SDDiver5]

Just did this but on my F150. Went from 3:31 OEM gears and open rear to:
4.56 gears
Eaton E Locker

The shop who did the work suggested E Locker over air locker due to failure points in air lines. I also wanted a selectable locker over an LSD for more control. I'm 100% sure the locker and gear options for a JKU are 1000/1 compared to the F150. I was pretty limited with Fords newish super 8.8 rear axle and gear options but the shop found some.

I run 315 tires with a 2.0 Fox lift/level. The difference is absolutely amazing and I wish I did it sooner. I went from constantly shifting with my 315's to cruising 2k RPM on the freeway and passing with absolutely no issue. I'm only just over 1000 miles on the regear and haven't towed with it yet or engaged the locker but soon will.

To get the best advice, you might want to ask a Jeep or JKU Specific forum or a shop that does Jeep work.

 

[Jupiter58]

Need some advice. Recently bought a 2007 JKU. It is completely stock with 3.21 gears. This isn't going to work. The plan is 2.5"-3.0" lift with 35" tires and the ability to tow a teardrop trailer with gear and 5 people. Looks like the two best options will be 4.10 or 4.56 gears. Anyone have similar setups that can share thoughts?

Also, will plan to do lockers while I'm at it. I haven't done any research here yet, but if you have suggestions, my ears are open. I prefer simple and failproof to more complex/fancy options. Thanks!

Towing with 35s you should go straight to 4:88s, some would say 5:13s with all those people.
That’s with an auto tranny.
A jeep is not a great tow vehicle to begin with and you will be well over gvwr with 5 people and gear. I wouldn’t plan on towing anything bigger than a small off road trailer with mine.

 

[rplowden]

Thanks for the advice. I should have mentioned it's a manual, so I know it shifts the power range slightly. I appreciate y'all.

 

[jadmt]

Definitely at least 4.88. check out Wrangler forum.com for lots of good jk information

 

[zgfiredude]

Here is a link the a gear ratio chart, below......look for the 3.8 and the manual tranny and then choose your tire size. Generally speaking the 3.8 is considered a bit more sluggish than the 3.6, so I'd focus on leaning up a gear size if in between two choices. Chart

I have a 3.6 automatic, 3" lift and 34" tires, 4.10 factory gearing. I also pull a teardrop trailer frequently. It only weighs about 1500 to 1600 lbs.......the 4.10s are BARELY adequate. I "feel" like 4.56 is the choice but in my heart know that 4.88 is likely the better choice.

 

[billiebob]

5 people, a teardrop, and 35s.... I doubt you can legally carry that much but if you pack like a backpacker,,,,
2007 JKU is definitely not a powerhouse I'd definitely want at least 4.88s since you are living on the edge.

I'm not sure a 3" lift will work right with 35s, I'd pick 33s with a 3" lift.

Go here.... figure what rpm you want to cruise at. With your load and tires I'd never want to be under 3000rpm. Maybe calculate for that ideal rpm in 5th gear which is more efficient than 6th, save 6th for the long downhills when you can use overdrive.

Gear Ratio Calculator

 

[thewas4x]

Speaking from experience of having built several 3.8 powered JKs on both 35s and 37s, you will need 5.13s at minimum. Towing or not. That engine runs smooth enough and needs the increased RPM to be in a better part of the torque curve. I'm not sure even 5.38s would be out of the question if you're planning to tow regularly. RPM will be your friend with that 42RLE transmission and its deep overdrive. 4.56 or even 4.88s will not get it done.

 

[thewas4x]

Wait, 6-speed manual, I missed that, maybe 4.88s would be okay. The auto needs way more help than the manual.