Technically, the D30 and the D30JK are what they are called, they have subtle differences. The D30JK is definitely more robust, however it still suffers from a small ring and pinion size. Though most reference material classify them both as a "D30". IMHO, the lowest practical gearing on a D30JK is 4.88's (IMHO, if you plan on going offroad) due to the super-small pinion size of the 5.13's. Hell, even the D30JK 4.88 pinion is super small compared to stock gearing. Hence, the trend to go with larger axles as the gears go down (numerically higher). 5.13's, IMHO, should require a D44JK. I've heard of 5.38's for the D30JK, but I wouldn't touch them.
As a matter if fact I recently had to get one differential rebuilt. Nope, it wasn't the front. My rear D44 had problems with the gears and the factory limited slip. I had the bearings and seals changed again, new Yukon gears replaced the superior gears, and since it was apart anyway, I had a Yukon zip locker installed which is an air locker very similar to an ARB but a few hundred dollars cheaper.
It is worth noting I don't crawl on rocks and I am a flat lander and mud bug. I also tow and enclosed trailer.
I haven't had a chance to really use the locker other than brief testing but it seems to a quality piece with smooth operation. I was expecting it to be clunky but is so smooth you can't feel or hear it engage.
__________________ 2014 Copperhead Pearl Unlimited Sahara in progress
I'm quickly coming to the conclusion that 4.88 is ideal for my needs. My wife complains that the Jeep is too tall to get into. There's virtually no way that I'll move up to 35's.
Several people have said that 4.10's with 35's is a good combo for the 2012-2013 5 speed auto. With that set up at 2,200 RPM the Jeep should be doing 67 MPH, in 5th gear and 15 MPH in 1st. A 2007-2011 with auto tranny and 4.88 gears would do 67 MPH in 4th gear and 16 MPH in 1st at 2,200 RPM. Running 33's as I am now would have the RPM ~6% higher (2,333 RPM to be precise), which is manageable. If I ever decided to go to 35's it'll be set up to handle them.
I have a 2012 unlimited with3.6L 6speed manual and 3.21 gears. I have installed a 4" lift and 315x75x16 tires. I have lost a lot of power and torque. I want to regain the power without compromising gas mileage too much. I am either going with 4.56 or 4.88. Which is better with the 3.6 pentastar, 6speed manual, Dana 30 front, Dana 44 rear and the tires I have on the jeep? Also, does anyone have a reason why I should not go with detroit lockers?
Well itís a rare occasion indeed when spyder6 and me agree 100% on something and this is one of them.
Although the detroit locker is a little more user friendly on a long wheelbase vehicle like the JK it still will be annoying on the street plus you will have to adjust your driving habits to counter the way it makes your Jeep handle.
Best to invest in a selectable locker and have the best of both worlds; it will be money well spent.
Does detroit make a locker that is not a limited slip differential (trutrac). I have been told that they have lockers that are truly open when not engaged and locked when engaged. True they are electronically activated and not air like the ARB, but wondering if they will hold up like ARB? Kinda new to the forum and Jeep community. Loving all the smiles and waves I get from other Jeep wranglers going down the road. It truly is a "JEEP THING".
So what these charts are telling us is that the creator of the chart believes that 99.9% of all JK's, with 3.8L motors, were improperly geared when built (I'll leave room for 0.1% to be "properly" geared due to customer orders)? I'm having trouble believing that.
I picked up a 2013 JKU Rubicon 10A which stock it has the Auto Trans with 4:10's in the pumpkins. My wife uses the Jeep for her daily driver (for the time being and she needs a dependable snow driver for the winter) but I live 45 minutes from the Rubicon so I'll be using it for my weekend 'Con runs. I thought my plans were to install 4:88's with 35" tires which I felt the 4:88's would leave enough meat on the gearing because I'm concerned breaking pinions due to the lack of strength/meat left on that kind of tall gearing. After reading this thread I'm on the fence now. Has anyone changed out their gearing to 5:13's and use it for their DD along with good off-roading?? Have any problems?? Any suggestions?? I've had quiet a few 4WD's and I'll have to admit this is the one that is spoiling me the most. Wish they covered more with skid plates the way I drive off-road but we'll fix that. One of the problems I'm having with it is trying to get it away from my wife. At first she wasn't interested in driving it but now... Thanks in advanced.
Rock-Rocker, I would not worry about the pinion being too small. At 4.88 the pinion is still very thick.
I am running 5.38's and have snapped the rear D44 axle shaft, but the pinion did just fine. Honestly, I have rarely heard of anyone snapping a pinion, even 5.38's. Others may have different stories, though. Usually, it is the axle shaft that goes first. You should be fine with 4.88's, unless you are attacking Moab like a monster truck on Red Bull & Crack.