Jeep JK Wrangler Axle Basics

With more and more people building up their Jeep JK Wranglers and getting them to sit on 37″ tires or larger, it’s no wonder that so many members of have made axles and the components that make them what they are, one of the hottest topics of conversation. Whether it be in regards to installing new gears, upgrading axle shafts or replacing them altogether, people are looking for answers and in more cases than not, I have found that they don’t even know what questions to ask. Of course, a lot of this is because the subject of axles is completely Greek to them.     Thanks to the help of David Castillo from Currie Enterprises, this article was written to help provide some basics about front and rear axles. Our goal is to help educate people, give brief overviews of the major components that make axles what they are and to provide a reference point to work off of.

Quick Reference Guide

The diagrams below will help you to identify an axle at a glance by determining the shape of it’s differential cover.

Dana 30
Dana 35
Dana 44
Dana 60
While the Dana 44 and Dana 60 look very similar, the difference between the two can be seen in the Dana 60’s significantly larger size.

Common Axle Terms

AUTOMATIC LOCKER – traction control device that locks and unlocks the differential automatically with no direct input from the driver.    BACKLASH – The amount of clearance or play between the ring and pinion gears.BEARING CAP – Component within the axle housing that is bolted in place to secures the differential bearings and differential assembly in place.

BEARING CONE – The inner race of a tapered roller bearing.

BEARING CUP – The outer race of a bearing assembly.

CARRIER – The casting center section of a drive axle that contains the differential assembly, ring gear, pinion gear and support bearings. (NOTE: the term ‘CARRIER’ is often times used to describe what is know as the ‘DIFFERENTIAL’)

CHROMOLY – An abbreviation for “chromium-molybdenum steel” (sometimes spelled “cro-mo”). Chromoly is a range of low alloy steels that is not as lightweight as aluminum alloys but has the advantages of high tensile strength and malleability. It is also easily welded and is considerably stronger and more durable than standard 1020 steel.

DIFFERENTIAL – The gear arrangement inside the center of a drive axle that allows the drive wheels to be driven at different speeds and divides the input torque of one shaft between two output shafts. Also known as the “pumpkin.” (NOTE: the ‘DIFFERENTIAL’ is often times referred to as a ‘CARRIER’)

DIFFERENTIAL COVER – The outside cover that is bolted onto the open face of the carrier. Also known as a ‘DIFF COVER’

END YOKE – Yoke-shaped forging that forms part of the universal joint connection on the front axle shafts.

SHIM – Thin spacer used to adjust preloads and ring gear to pinion gear backlash. May also be used for controlling pinion gear positions.

GEAR – A wheel with teeth that transmits power or motion to another gear.

GEAR RATIO – The ratio in the number of teeth on the ring gear and the pinion gear.

HOUSING – Portion of the axle assembly that consists of the carrier and axle tubes.

LIMITED SLIP DIFFERENTIAL – Differential in which the difference in rotational speed or torque between two output shafts is mechanically limited to prevent wheel spin on difficult terrain.

LOCKER – A variation of the differential, a locking differential restricts each of the two wheels on an axle and forces them to rotate at the same speed without regard to available traction or differences in resistance seen at each wheel.

PINION GEAR – A small gear that meshes with a larger gear.

PRELOAD – A load placed on parts during assembly to maintain critical clearances and adjustments when operating loads are applied.

RING GEAR – The large gear that is attached to the carrier and meshes with the pinion gear.

SELECTABLE LOCKER – Traction control device that allows the driver to lock and unlock the differential at will from the driver’s seat.

SPLINE – Thin narrow groves created on the end of a shaft that allows it to mate perfectly with matching groves on another component.


Special Thanks

I’d like to give special thanks to Currie Enterprises and David Castillo for taking the time and helping to help make this axle basics article possible.

JK Axle Overview

Dana 30 front axles have a 7-1/8″ diameter ring gear and come standard on Sahara and X model Jeep JK Wranglers with a gear ratio of 3.21. For 2007, an optional 4.10 gear ratio was available on towing packages. In 2008, this was changed and the only optional factory gear ratio now available is 3.73. Dana 30 front axles do not come with any limited slip or locking differentials.
Dana 35 rear axles have a 7.56″ diameter ring gear and only showed up on a few 2007 Sahara and X model Jeep JK Wrangler 2-Doors before being replaced by Dana 44’s. These were available with a 3.21 and an optional 4.10 gear ratio.  No limited slip or locking differential was offered for it. (NOTE: Photo taken off a TJ Dana 35)
Dana 44 axles have an 8-1/2″ diameter ring gear and now come standard on the rear end of all Jeep JK Wranglers. Sahara and X models come standard with 3.21 gear ratio. In 2007, optional towing packages were available with a 4.10 gear ratio. In 2008, the only optional factory gear ratio available is now 3.73. A limited slip differential is available as an option and as of 2008, a selectable electric locking differential is available as an option as well. All Rubicon model Jeep JK Wranglers come standard with front and rear Dana 44 axles, a 4.10 gear ratio and selectable electric locking differentials.
Dana 60 axles have a huge 9-3/4″ diameter ring gear and are typically found on vehicles such as 3/4 ton pickups and cargo vans because of their strength. Likewise, aftermarket Dana 60 axles such as Currie Enterprises’ Rock Jock 60’s are what JK owners will be wanting to upgrade to once they get their rigs sitting on top of 37″ or larger tires and playing hard on the rocks. Available for the front and rear and built to order, you can get a set of Rock Jock 60’s with chromoly axle shafts, a 5.13 or 5.38 gear ratio, locking differentials and up front, with 1-Ton knuckles and more.

Axle Components Visual Reference

This photos illustrates what a set of Dana 30, Dana 44 and Dana 60 ring and pinions with a 4.10 gear ratio looks like side by side. As you can see, there is a significant difference in size and thickness.
Here you can see what a Dana 30, Dana 44 and Dana 60 open carrier looks like as well as the differences between them. The ring gear is bolted onto the differential and is what you would see inside your carrier. The ends of your axle shafts get inserted into the ends of the differential.
These two photos show the inner and outer halves of a standard Dana 30, an AlloyUSA JK chromoly Dana 44 and a Dana 60 front axle shaft. As you can see, the Dana 44 and Dana 60 inner shafts are blanks ready to be splined but you can easily see how much thicker the shafts are over a standard Dana 30 axle and how much more built up the yokes are as well. Dana 30 shafts have 27-splines and Dana 44 factory front axles shafts are 30-spline.
This is a side by side photos of a standard Dana 30, Dana 44 and Dana 60 front axle shaft U-joint.
This is a shot of a Superior chromoly replacement Dana 44 35-spline axle shaft sitting next to a Currie Rock Jock 60 shaft. Unfortunately, I did not have a factory shaft to compare them to but I can assure you that these two shafts are significantly beefier. Factory Dana 44 axle shafts are 32-spline.

Upgrading to a Currie Enterprises
JK Rock Jock 60

When it’s time to upgrade your axles to a Dana 60, few manufacturers make one as complete, featured fill and stylish as the Currie Enterprises Rock Jock 60. The photos below highlight some of the features you can expect with yours.

This is a shot of what the Currie Enterprises Rock Jock 60 front axle housing looks like with a standard small knuckle or “axle C”. If you’re going to install a Currie Enterprises Rock Jock 60 front axle, I would highly recommend that you do it right the first time and order yours with 1-Ton knuckles as shown in this pic. The up turned differential cover is a signature element of the Currie Enterprises Rock Jock 60. Here is a shot of a front axle with upper control arm mount attached to the differential cover.
Currie Enterprises Rock Jock 60 axles come complete with all the brackets you need to bolt it up to your Jeep JK Wrangler. For added strength, these brackets are reinforced as shown in this pic. Both front and rear Currie Enterprises Rock Jock 60 axles come with skid plates that wrap around the base of the differential as shown in this pic. The Currie Rock Jock 60 axle also come with added features such as a track bar, swaybar link and shock mounts that have multiple mounting locations to provide fine tune adjustments.
As mentioned, Currie Enterprises Rock Jock 60 axles come complete with all the brackets necessary to bolt it up to your Jeep JK Wrangler. Also, your factory brakes and rotors will be re-used so you will not need to address them either. However, you will need to buy a carrier or locker like an OX, ARB or Detroit as well as a set of axle shafts to complete your new axles.     If you have any questions about Rock Jock 60 axles, you can contact Currie Enterprises directly

Whether you’re going to install a set of aftermarket chromoly axle shafts, replace your entire axle assembly altogether or maybe just help it along by installing a locking differential, it is my hope that this article will help assist you in determining what you will want to do. So you all know, I will try to update this article as more information comes my way.




  1. Thanks for the write-up, this is exactly the type of thing I had in mind when I pm’d you a while back with that spline question.

  2. absolutely awesome Eddie, this should be a mandatory document to be read by all newbies

    great job on this

  3. Hi to all JK drivers and Jeep fans.
    First of all I like to bag for your pardon for my poor english and send you best regards from Germany, especially from the Jeep Club Germany.

    In about 6 month I´am going to replace my WH Grand Cherokee 3.0 CRD with a Jeep JK Wrangler Unlimited Rubicon 2.8 Diesel with manual 6 gear transmission. But compared to the rock crawling pimps which are discussed here mostly, I like to build up a long range and desert travel Wrangler. This means Long Ranger Fuel Tank, OME heavy duty springs, koni heavy track shocks, black widow storage system with 70liters water tank, Safari Snorkel with zyklone, 35″ tiers, K&N air intake filter, additional fuel cleaner, Warn winch and ARB bumper, dual friction clutch, park heating, two optima batteries, special batterie charging system, roof rack, Tom Woods drive shafts and so on and so on.

    But this not the story – I need your assistance, experience and support concerning the axles. The Dana 44 new generation axles will be fine in the front I hope. But for the rear axle I`am thinking about upgrading to the dana 60 or maybe just changing the 44 to a superior chromoly axle shaft.

    I hope you could help, even if I like to use my jeep differently to the rock crawling – in the end it must be a durable long travel offroader, which can be used with the needed additional load for a two week trip, thousands kilometers and tough speed trough the african desert dunes and humpy dirt tracks.

    Thanks a lot in advance for your serious support – Steven.

  4. I have an 08 JK X model that I would like to put 35″ tires on. I have been told that the dana 30 that is on the front will not be strong enough and that I will break axles. What is a good guide to know what size tires can go with they type of axles? Last thing I want to do it get on the trail and break due to poor design.

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