2012 Jeep Wrangler: Transformed with 4.10 Rubicon Crate Axles
by Dan Edmunds, Director of Vehicle Testing on January 15, 2016
A 2012 Jeep Wrangler Sport once lived in the Edmunds long-term test fleet. It still does, in a way, because I bought it for my very own. And I'm still tinkering with it, which is still relevant here because a 2016 Jeep Wrangler is essentially the same machine.
My main beef with the stripped-down Sport we bought has always been its lame 3.21-to-1 axle gearing, an overly-tall ratio meant to maximize the Wrangler's window sticker fuel economy at the expense of off-road performance. Back in 2012, a mere $50 would have netted us a 3.73-to-1 axle gear option that would have rectified that, but we didn't bite (note: the same 3.73-to-1 option now costs $695 on a 2016 Wrangler Sport, but that's a story for another post.)
The long-leggedness of the 3.21 gears was less than optimal in certain situations with the factory 29-inch tires they came with, but it became downright intolerable after we fitted taller 33-inch BFGoodrich off-road tires. And this was no longer just an off-road shortcoming.
It became tricky to depart a stop sign without deliberate and somewhat questionable clutch tactics, and sixth gear wasn't useable at speeds below 65 or 70 mph.
The differentials desperately needed to be cracked open and re-geared, but as it turns out the 3.21 axles have a serious physical limitation: their internal design makes it nearly impossible to go beyond 3.73-to-1, their so-called "carrier break" point. This might have been OK had we still been running 29-inch tires, but it wasn't going to be enough with our 33-inch tires. We needed to go bigger.
Besides, a Wrangler Sport like mine (or a Sahara) comes with a light-duty Dana 30 front axle. Re-gearing for off-road performance doesn't make much sense without a complete upgrade to a more robust Dana 44 front axle assembly. In retrospect, our failure to spend the $50 for 3.73-to-1 Dana 30 axles only made my current decision that much plainer.
What I resolved to do was obtain a pair of complete axles from a Wrangler Rubicon, a direct bolt-in swap. These are Dana 44 units, front and rear. They have 4.10-to-1 gearing. They have electronically lockable differentials. And if I ever decide to go truly nuts, these axles reside on the happy side of their carrier break point and can be upgraded to 4.56, 4.88 or even higher.
Mopar sold exactly what I wanted in the form of complete "crate axles" back in 2012, but we balked at the cost of more than $3,000 — each. So I prowled Jeep forums and Craigslist for months, looking for Rubicon take-off axles being sold by a more intensely dedicated (and presumably wealthy) Jeeper that had upgraded to reinforced aftermarket Dana 60 custom axles.
Shipping such heavy items is prohibitively expensive, so I had to confine my search area to places I'd be willing to drive. This reduced my chances markedly. On those rare occasions they did pop up, and when I saw the listing in time, the sellers invariably wanted $2,500 or more apiece for what usually turned out to be well-used units that had been beat on. No thanks.
And then something extraordinary happened in 2015: Mopar dropped their crate axle prices significantly. Brand-new Rubicon Dana 44 e-locker axles tumbled to $2,395 for the front (part number P5153825AF) and $2,100 for the rear (part number P5153826AB), about a grand less apiece than they'd been when I'd first looked into it. And those prices included shipping to the dealer of my choice.
You order them through your local Jeep parts department as you would any other Mopar accessory or special-order part. I suppose you could work out an installation price with the service manager, but I didn't inquire. I had always planned to haul them to the shop and install them myself, and I used our 2014 Ram 1500 truck to pick mine up once they came in.
They keep the price low by configuring them exactly as they would supply them to the Wrangler Rubicon assembly line. For workflow reasons known only to the assembly plant's manufacturing engineers, the front axles are delivered without brakes but the rear ones include calipers and rotors. But I didn't want to crack open any brake lines and re-bleed the brakes during the swap process, so I stripped off the new rear brake calipers and reused my old ones.
I had to drill a few holes to accommodate the limit straps and spring retainers of my existing lift kit, but this was much easier to do off the car than it had been when I first installed the lift kit three years ago.
In the end this was a solid eight-hour job, even with access to our Rotary Lift and a second pair of hands — both of which seem essential. Call it six hours if you deduct my specific lift kit mods and the unrelated spring change I decided to make while I had the thing apart. Either way this is a straightforward, yet clumsy process involving heavy components and numerous critical nuts and bolts to disconnect, reconnect and re-torque.
The result has been transformative. Stop-sign launches require no thought at all. With the old 3.21s and the big tires, the engine lugged at a lowly 733 rpm at 5 mph, but my new 4.10s have brought that up to a more comfortably stable 936 rpm. And I've got sixth gear back!
On the freeway, 65 mph used to come at a loping 1,700 rpm, a speed at which the engine was not able to deal with any sort of hill or roll-on acceleration. I found myself downshifting a lot more than should have been necessary. Now it purrs along at 2,200 rpm at that speed and can easily pull sixth gear at just 55 mph and 1,850 rpm.
Will fuel economy be worse? Maybe not. Before the swap I found myself cruising in fifth gear a lot of the time, with the revs at 2,150 at 65 mph — the same rpm I'm at now, more or less. It's more like I've gained a gear and can now enjoy the drivability benefits of a close-ratio gearbox.
On paper, my new low-range crawl ratio has improved from 38.9-to-1 to 49.7-to-1, but I have not yet wired up my new electronic locking differentials and got them working. A hard-core off-road test at someplace like Moab is still off in the future, but I fully expect to be completely satisfied. Heck, I already consider my crate axle swap to be a worthwhile expense based on what I've experienced so far on pavement.
Dan Edmunds, Director of Vehicle Testing @ 35,455 miles