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Jeep Wrangler Axle Wrangling - Part 1

Posted in How To: Transmission Drivetrain on March 14, 2014
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Photographers: Courtesy Of The Manufacturers

Safety and reliability are the two most important build parameters. We want to be able to wheel hard on the weekend, but still make it to the office Monday morning. The more you push your rig off-road, the faster you will find its so-called soft spots. For many, an expensive, but common weak link is the stock rear axle. And depending on your specific wheeling rig, aftermarket axle support is either overwhelming or nearly non-existent.

While it’s difficult to pick which axle is the right fit for every rig, there are important parameters to help narrow the field. Requirements such as ABS, speed sensors, and specific bolt patterns can knock out many junkyard options. Factoring in tire size, axle width, vehicle weight, and whether you plan to upgrade your front axle down the line are also part of the overall axle equation. Oh, yeah, and there’s that whole issue of cost!

We’re no strangers to swapping in axles, and as is the case with many of you, our rigs are constantly changing and evolving. Take our ’97 Jeep Wrangler for example. Starting out with a 2.5L four-cylinder TJ, we’ve spent the past few years slowly transforming our cream-puff Wrangler into a formidable wheeling machine. A few years ago, we finally ditched the stock axles in favor of a pair of Trail Series 44 axles from Dynatrac. The Next Generation-style 44 axles use the larger Dana 44 gears, axleshafts, and lockers found in the ’07-current Jeep Wrangler Rubicon.

At the time, the NG Dana 44 axles fit our needs perfectly and remained trouble free for many years. Eventually, our Jeep received a heart transplant that changed things quite a bit. Our new life source was a 5.9L V-8 from a ’99 Dodge Durango. With the engine conversion came 37-inch tires, and of course, a heavy dose of power! After breaking a few axle parts and toying with larger tires, we decided to start our search for a stronger axle set that could fit our Wranglers growing needs.

There are literally dozens of axle options for the Wrangler platform. So many in fact, we decided to narrow the field slightly. Our main exclusion was high-pinion rear differentials. Why? Partly because Technical Editor Mansour prefers low-pinion rear axles, and since our Wrangler’s wheelbase is stretched, the necessity of a high-pinion is greatly reduced (read more in the low- and high-pinion sidebars). Looking at low-pinion rear axles also allowed us to include more budget-friendly junkyard alternatives.

Ultimately, our next rear axle needs to be able to handle V-8 power, 37- to 42-inch tires, and support a vehicle that hopefully will never weigh over 5,000 pounds. We’ve narrowed our field of axle options to two aftermarket and two junkyard selections. Each has a strong case for making it under our Wrangler, but only one will take the cake. Be sure to check back for our next installment as we show you our axle of choice and what it took to place it under the Jeep.

Budget: Filet Mignon
Who: Dynatrac
What: ProRock 80
Why: If the 14-bolt is the ultimate junkyard axle, then Dynatrac’s ProRock 80 might just be the ultimate aftermarket rear axle. It’s worth noting that Dynatrac offers low-pinion 60 and 70 rear axles that fit our criteria as well, but the allure of a practically indestructible ProRock 80 is hard to resist. With a massive 11.25-inch ring gear and 4-inch axletubes, the ProRock 80 is designed to handle everything from 1-ton diesel trucks to mega-built wheeling machines. With only 1-inch less clearance than the ProRock 60 housing, the ProRock 80 provides ground clearance that other 1-ton axles can’t touch. Gear ratios go up to 5.38 and options include disc brakes, custom widths, 35- or 40-spline axleshafts, and a traction aid of your choice. The massive full-float ProRock 80 would require us to change wheels and bolt patterns, and the added weight would be a little unwelcome. Overkill, sure, but sometimes that’s OK.
Contact: Dynatrac

Budget: Hamburger
Who: East Cost Gear Supply
What: Semi-float Dana 60
Why: East Coast Gear Supply’s semi-float Dana 60 is offered as a bolt-in upgrade for the ’97-’06 Jeep Wrangler TJ. The semi-float design uses Set 20 bearings (also known as “Big Bearing” outers) commonly found on fullsize trucks. The semi-float design is much lighter than that of a full-float 60, and more than capable of supporting our Wrangler. The Ford 8.8-inch disc brake kit that comes with the axle would allow us to retain our stock e-brake cables and not overwhelm the factory master cylinder. Each axle comes with 35-spline chromoly axleshafts standard, which are drilled for 5-on-5½ and 5-on-4½. This means we could keep our current bolt pattern and wheels. Gear ratios from 3.55 to 5.38 are available along with a variety of traction aids and differential covers. The cast Dana 60 differential doesn’t have as much ground clearance as some of the high-pinion units on the market, but the strength trade-off with the low-pinion gearset is worth it to us.
Contact: East Cost Gear Supply

Budget: PB&J
Who: Dana-junkyard
What: Full-float Dana 60
Why: The Dana 60 rear is an easy junkyard find. Placed under Ford, Dodge, GM, and Jeep platforms, you can source a full-float low-pinion Dana 60 rear with relative ease. The aftermarket support for these axles is tremendous, but not all are alike or desirable. Most are fitted with heavy drum brakes, which is something we would definitely ditch. Finding one fitted with 35-spline ‘shafts is more difficult, as the majority were fitted with 30-spline ’shafts. Moving up to 35-spline axleshafts would require machine work, but we could convert the axle to a semi-float rear at the same time with readily available aftermarket axleshafts.

Stock semi-float versions do exist, but most are C-clip, so, no thanks. Maybe the two biggest hurdles are axle width and bolt pattern. You can pay to have the axle narrowed to come in closer to the Jeep’s stock width, but it takes away some of the low-buck aspect axle. And machining the hub or purchasing an aftermarket unit to make it five-lug won’t be cheap. This axle is best suited for those looking to move to full-width axles and don’t mind jumping up to an eight-lug bolt pattern. Under a lightweight vehicle, the full-float 60 can easily handle our needs, but we’re still not sold that it’s the right one for us.

Budget: Ramen Noodle
Who: GM
What: 14-bolt
Why: When it comes to strength, availability, and price, it’s hard to beat a GM 14-bolt. An extra pinion support, 10½-inch ring gear, 1½-inch axleshafts, and incredible aftermarket support have made the 14-bolt one of the top go-to rear axle upgrades. You can grab a 14-bolt from under ¾- and 1-ton GM trucks, vans or SUVs. Later-model axles will even have disc brakes, but easy-to-source axles will have drums. With a max torque rating of 6,242 pounds, the 14-bolt is equally as overkill as the ProRock 80 for our light Jeep. The fact that it would allow us to move in any direction from mega mudder to crazy rock bouncer does draw us in. The narrowest you will find a 14-bolt is 63 inches and from there it moves out to roughly 73 inches. Full-width and eight-lug is where you will be with this conversion, so for a rear-only swap, it isn’t as desirable. Ground clearance is also a concern as the housing is larger than that of a standard Dana 60. You can gain a little clearance back by shaving the bottom of the housing, but again, time and expense can add up. At the end of the day, the 14-bolt has a lot going for it.

The drawback of the high-pinion rear diff is that it runs on the weaker (coast) side of the ring gear. For a heavy vehicle, this can equate to a demolished ring-and-pinion, even with something as tough as a Dana 60. Lighter rigs with modest horsepower and tire sizes are the best fit for a high-pinion rear. If you are unsure if high-pinion is right for your vehicle, the best advice is to take your 4x4 to the scales and discuss your vehicle with the axle manufacturer to ensure that your rig is getting what it needs.

Modern 4x4s are saturated with electronics. Differential tone rings, wheel speed and ABS sensors are not something that can be ignored or overlooked. We’re lucky that our Wrangler’s lone VSS (vehicle speed sensor) is attached to the transfer case and ABS is non-existent. For vehicles such as the ’07-current Jeep Wrangler JK, late-model Ford F-series, Rangers, and many others, installing axles without appointments for tone rings and sensors can cause the vehicle to not operate and the dash to light up like a Christmas tree. Many aftermarket companies offer axle assemblies that can accept your vehicles sensors. Outfitting junkyard axles with the correct sensors is becoming increasingly popular, but the aftermarket is still slow to release parts that can retrofit old axles in new rigs.

Semi- or Full-Float
To determine whether your rig warrants a full-float or semi-float axle, it’s important to understand the differences between the two. In a semi-float axle (the most commonly found rear axle on ¼- and ½-ton trucks and SUVs) the axleshaft and a single wheel bearing on each side work together to support the weight of the vehicle and propel it. On a full-float axle, the load carrying portion of the axle is performed by hubs that ride on spindles on either side of the axle. Inside each hub are two bearings that are designed to support more weight over a standard semi-float axle design. In a full-float configuration, the axleshaft attaches to the hub separately. This allows the axle to solely handle the propulsion and the hubs weight carrying duties. A full-float axle will be stronger, but under a light rig such as our Jeep Wrangler TJ, it is overkill. Many aftermarket axle manufacturers suggest moving to a full-float axle for vehicles climbing above 4,500 pounds.

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For those looking at aftermarket axles, you’ll notice that high-pinion differentials actually outnumber the amount of low-pinion diffs being offered by the aftermarket. A high-pinion means that the pinion is placed above the centerline of the axletube. In the front of a vehicle a high-pinion (which uses a reverse-cut gearset) turns on the stronger drive-side of the ring gear. Some of the advantages of using a high-pinion rear diff include reducing the driveline angle along with raising the driveline to keep it out of harm’s way. Most of the aftermarket high-pinion differentials also provide greater ground clearance over a conventional differential.

Peek under the rear of nearly any stock 4x4 and you will undoubtedly find a low-pinion differential resting out back. A low-pinion differential uses a hypoid-style gear cut, which when placed in the rear of a 4x4, applies pressure to the stronger drive side of the gear. Since the pinion generally sits below the centerline of the axletubes it places the driveline lower and can hinder ground clearance. High horsepower, heavy, and rigs constantly living off of the rev limiter are all appropriate candidates for a low-pinion rearend. Given the fact that it’s all you will find in the junkyard, the low-pinion actually wins out on the strength and budget front as well. In case you didn’t know, flipping a low-pinion upside-down does not make it a high-pinion. Doing so will actually make the wheels turn the opposite direction! Also, a low-pinion gearset will not work in a high-pinion differential.

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