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2.5-Ton Axle Building Tips For TTC

Posted in How To: Transmission Drivetrain on July 1, 2010 Comment (0)
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If ever there were a perfect axle for the massive rigs found at Top Truck Challenge, it would probably be the Rockwell 2.5-ton. Few others can handle the high horsepower and torque loads required by the behemoth tire sizes found at TTC. Where even the toughest Dana 60 can snap like a twig, the massive Rockwell 2.5-ton runs strong. These assemblies are gigantic and not for everyone. But if 46- to 54-inch-tall tires are your goal, and competition is your game, the stout deuce-and-a-half axle may be the next swap you should consider.

With each passing year, TTC rigs have only seemed to grow larger. As proportions increase, so do the demands on drivetrain components. We have often wondered if someday we will see nothing but Rockwell axles under our top ten vote-getters at TTC. In '09, five out of ten competitor rigs had grown past the traditional Dana/1-ton running gear to the superior Rockwell axle sets. Shown here is Brett Jerome's custom Jeep buggy on 54-inch Baja Claw TTC tires as he negotiated our Mini-Rubicon boulder field.

One key factor that makes the Rockwell axle desirable for TTC truck builders is the top-loading third member design. Well beyond that of a high-pinion Dana axle, the Rockwell features an input shaft that is mounted a full seven and a half inches above the center line of the axle housing. above the axle housing, allowing for super-flat driveshaft angles. Thanks to very healthy support from the automotive aftermarket, a Rockwell axle can be as easy to build as a Dana 60, as long as you have a forklift to move it. Is it the ultimate axle solution? No, but depending on how you build one, a 2.5-ton Rockwell could be the last axle you'll ever need.

Ultimate strength comes at a price, and in the case of uber high-end Rockwell axle parts, the price is justifiability higher than that of an equally high-end Dana 60. The same can be said about the weight. For example, where a complete front Dana 60 axle might weigh somewhere in the neighborhood of 600 pounds, a Rockwell frontend tips the scales at just over 1,000 pounds. In the battlefield of TTC, smart drivers with big tires, big power, and even bigger axles always seem to eclipse the competition. As such, we have assembled a buyer's guide that caters especially to those would-be Rockwell axle builders.

Build Strategy 1 - Unlimited Budget
A TTC Proof 2.5-ton
If a TTC-taming Rockwell axle is what you need, and you have an unlimited budget, the place to start is Ouverson Engineering and Machine. Ouverson has been building custom Rockwell upgrade parts for over five years now. Today, you would be hard-pressed to find a Rockwell axle at TTC without at least one part from Ouverson. Owner Randy Ouverson started his business out of necessity after breaking everything else on the market. His dedication and innovation throughout the years have transformed the readily available 2.5-ton Rockwell axle from a heavy military surplus part into a high-end, virtually unbreakable solution for seriously competitive enthusiasts. Today, even some of the working pros on the monster truck circuits run Ouverson parts. In the last year and a half, Ouverson's product portfolio has expanded threefold. With so much new product available, it is hard to keep up. We therefore decided to dedicate the first part of this story to Ouverson's latest and greatest Rockwell offerings.
Info: Ouverson Engineering and Machine, 320/983-3030,

What is it: Ouverson's Billet Steering Knuckles
Why it is cool: A high-end housing like the one shown above begs for a pair of high-end billet steel steering knuckles. Ouverson offers these knuckles as an ultimate high-strength upgrade for those who want the best at any cost. With these knuckles, you can run stock Rockwell spindles and hubs, or you can upgrade to Ouverson's awesome Super 8 hub setup and convert over to the popular 8-on-6.5 or 8-on-170 mm lug patterns. These knuckles also allow use of Ouverson's 47-spline axleshafts.

What is it: Ouverson's Fabricated Rockwell Housing
Why it is cool: The heaviest part of the Rockwell axle is the housing itself. With this new fabricated plate housing, significant weight savings are attainable. It also allows for unlimited options in terms of fabricated link mounts and steering arrangements. The standard version comes in mild steel for front or rear applications and is fully welded and ready to assemble. Another version of this housing is available in lightweight chrome-moly for the ultimate in strength-to-weight ratio. Every axlehousing is built to suit, and they're available in custom widths for use with off-the-shelf knuckles and third members.

What is it: Ouverson's Violator Series Axle Conversion
Why it is cool: Most stock Rockwell axleshafts feature 16 splines. The Violator Series axleshafts feature 47 splines and come with a lifetime warranty against breakage. Included with this upgrade package are inner and outer shafts, seals and retainers, drive flanges, and your choice of locker or spool. Ouverson recommends upgrading to the Violator Series U-joint when performing this conversion.

What is it: Ouverson's 4.90:1 and 6.73:1 Gear Sets
Why it is cool: In stock form, Rockwell 2.5-ton axles come with a 6.72:1 ratio-not exactly a highway-friendly combination. Furthermore, the factory gears were designed with low-torque multi-fuel military engines in mind. Add additional power to the equation, and the stock gearsets start to wear out quickly and even break in some circumstances. The solution: replacement gearsets from Ouverson Engineering. Not only does Ouverson offer an all-new 4.90:1 ratio, but also the improved gear design enhances tooth engagement significantly over stock. Thanks to better materials, deeper tooth grooves, and a more robust ring design, the Ouverson gearsets can handle monster truck power and tire sizes without issue.

What is it: Ouverson's Third Member Stud Girdle Kit
Why it is cool: When you mix big tires with high horsepower, the stock Rockwell third member can develop problems. The excessive power causes the gears and bearings to deflect, resulting in improper wear and eventually failure of the third member. This billet steel Stud Girdle kit solves the problem by tying each side of the main bearing caps together, eliminating any possible deflection. The unit ensures proper gear mesh no matter how much torque the unit sees.

Build Strategy 2 - Working Man's Budget
A TTC Worthy 2.5-ton
When a Dana 60, 70, or 80 is not enough beef, but you don't want to sell the farm to afford the parts needed to go bigger, look into Boyce Equipment of Ogden, Utah. Boyce stocks new, rebuilt, and used front and rear 2.5-ton Rockwell axles that are ready to ship. Boyce also offers individual stock replacement parts like locking hubs, pinion-mounted brakes, third members, and seal kits to complete your Rockwell axle build. Boyce can also modify a Rockwell to your specs using custom axleshafts, U-joints, axle boots, wheels, or steering components-including full hydraulic conversions or any other part you might need.
Info: Boyce Equipment, 800/748-4269,

Finding Inexpensive Rockwell Axles
The military used 2.5-ton Rockwell axles in troop carriers for many decades. Today, these vehicles can be found rusting away in virtually every corner of the country. We found one listed for sale on the Internet for $1,000 or best offer. The only catch: This truck did not run and it was the buyer's responsibility to haul it away on a trailer. If you stop and think about it, three 2.5-ton axles for $1,000 is not a bad deal.

What is it: 2.5-ton Rockwell Rebuild Kit
Why it is cool: You get everything you need to ensure that your Rockwell axle is leak-free and ready for action on the trail. The rear axle kit shown here includes two spindle seals, two outer seals, two flange gaskets, one pinion seal, and one differential gasket. Kits are also available for front axle applications and include knuckle boots as well.

What is it: Complete Rockwell Axle Assemblies
Why it is cool: These axles are built using the latest and greatest factory-style internal parts and can be upgraded in many key areas for improvements in strength, traction, braking and steering. The best part about these assemblies is that you get outstanding upgrade in axle strength at an affordable price.

What is it: Boyce Equipment Rear Steering Lockouts
Why it is cool: If you would like to run four-wheel steering at some point, but only have the budget to set up the front axle with steering, check out this kit. This setup allows you to lock out the steering function of a front axle for use as a rear axle. Once installed, two simple lockout pins ensure that each knuckle remains straight for maximum safety.

What is it: Boyce Equipment's Ram Assist Steering Kit
Why it is cool: When it comes to 2.5-ton steering, ram strength and bracket placement is critical. Boyce Equipment developed a kit engineered to match the needs of the Rockwell axle in terms of steering sweep, bracket placement, and working pressure. The setup includes a single-ended ram, a control valve, and mounting parts to simplify the installation process.

What is it: Boyce Equipment Custom Rockwell Steel Wheels
Why it is cool: These custom steel wheels were designed specifically to work with the Rockwell 2.5-ton axle. Available in 15- to 25-inch diameter sizes, these wheels will handle plus-size tires without issues. Boyce Equipment also stocks all sizes of military tires, both new and used.

What is it: Boyce Equipment Rockwell Pinion Brake
Why it is cool: With this arrangement installed, you can eliminate the heavy old drum-style brakes and backing plates to lighten the axle for competition use. This kit includes all mounting hardware and the whole setup can be installed in minutes using parts left over from the stock drum brake system.

Rockwell Specific - Mounting Brackets
Blue Torch Fabrication (BTF) offers mounting kits to solve the problem of linking up a Rockwell axle. These brackets are designed exclusively for hardcore trail use. We have seen these brackets at TTC in the past and can speak to the quality and attractive design touches each includes.
Info: Blue Torch Fabrication, 866/725-2795,

What is it: Blue Torch Fab Rockwell 4-Link Towers
Why it is cool: All Rockwell axles came with leaf spring-style suspension arrangements. This poses a challenge for those who want to run coilovers, air shocks, and link arms. That is why BTF offers these laser-cut brackets designed to simplify setting up custom suspension systems. The tower bodies and lower link tabs of these assemblies are laser-cut from 3/8-inch-thick high-strength steel plate.

The towers and lower tabs have 9/16-inch boltholes for both upper and lower link attachment points. These brackets were designed to work with 1- or 1 1/4-inch rod ends with high-misalignment spacers or flex-joints. They provide 11 inches of vertical separation between the upper and lower links. The "towers" consist of six slotted pieces that fit together prior to welding, which makes assembly much easier. Sold in pairs, these brackets are the simplest way to link up a Rockwell axle.

What is it: Blue Torch Fab Rockwell Skid
Why it is cool: Due to the unique orientation of the Rockwell third member, the non-removable diff cover on the bottom of the housing is called a skidplate. The factory skid is stamped from thin sheetmetal and offers little protection from rocks and other trail obstacles. The BTF Rockwell Skid is precision laser-cut from steel plate. The 3/8-inch-thick base ring completely covers ring gear providing strong reinforcement rib for the 1/4-inch-thick side plates. The side plates protect the bearing caps, and the whole unit comes welded on each side. These skids are shipped unpainted and ready to weld in place of the stock unit. Simply cut the stock unit off and reinstall one of these heavy-duty skids to get awesome rock-resistant differential protection with added ground clearance.

Ballistic Fabrication offers an assortment of hard-to-find bracket kits designed to save fabrication time when setting up coil-sprung, radius-arm suspension systems on Rockwell axles. With a quick turnaround time, Ballistic Fabrication can also build one-off custom link arms and steering components to help you with your Rockwell axle needs.
Info: Ballistic Fabrication, 520/888-4441,

What is it: Ballistic Fabrication Rockwell Flat Bottom Radius Arm/Coil Mounts
Why it is cool: These laser-cut brackets make installing a radius arm-style suspension system on a Rockwell axle much simpler. Sold in pairs, these kits come ready to weld for a clean and simple mounting solution. These mounts are ideal for Ford Super Duty and early Bronco applications.

Stock 2-ton Rockwell Facts
Centersection: Double reduction-style. The upper ring-and-pinion gearset drives an intermediate gear that, in turn, drives the big, gnarly bull gear. The differential or locker is located inside the carrier on each side of the bull gear. Upper ring-and-pinion: 22 teeth on ring gear, 9 teeth on pinion = 2.44:1 Lower bull gear and intermediate gear: 33 teeth on bull gear, 12 teeth on intermediate gear = 2.75:1 Final gear ratio: 6.72:1 (combination of 2.44 ring-and-pinion and 2.75 lower gear)

Axleshaft: 1.62-inch, 16-spline
Differential: Open four-spider gear design
Bolt pattern: 6-on-8 3/4
Dimensions: Wheel mounting surface, flange-to-flange.
Front axle: 79 1/2 inches.
Rear axle, single wheel configuration: 69 1/4 inches.
Rear axle, dual wheel configuration: 79 1/2 inches.

What is it: Grizzly Locker
Why it is cool: This mechanical locker works with 16-spline axleshafts and features strong 8620 internal parts along with a patented internal design that reduces common failures associated with other Rockwell lockers. Targeted at the working man's budget, the Grizzly locker is the least expensive locker available for the Rockwell 2.5-ton.
Info: Yukon Gear and Axle, 800/347-1188,

What is it: Eaton's Detroit Locker
Why it is cool: Eaton offers the legendary Detroit locker for the 2.5-ton Rockwell axle in several configurations depending on which specific model axle you have. Models offered include 16-, 24-, 34-, 39-, and 46-spline counts; however, every Detroit Locker delivers 100-percent drive torque to both axles when power is applied. The design allows the tire on the inside of a corner to differentiate when making turns.
Info: Eaton, 216/523-5000,

What is it: ARB's Rockwell Selectable Air Locker
Why it is cool: At the push of a button, you can lock up both axles for ultimate traction on demand. When not engaged, the locker becomes an open differential-perfect for street-driven machines.
Info: ARB, 800/761-8159,


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