Author: Craig Perronne Photos: Craig Perronne
Big, heavy-duty trucks such as the Chevrolet 2500/3500 HD and the Dodge Ram 2500/3500 series are the backbone of the Dirt Sports Nation. Teaming with stout components and known for being able to take abuse, they are often put into service as tow vehicles or chase trucks laden with spare tires, parts and fuel. While not an easy life, it is task they are much more suited for than their lighter-duty ½-ton counterparts.
It was exactly for these reasons we selected a 2005 Dodge Ram 3500 Cummins four-wheel-drive as the basis for our Project Heavy Metal way back in 2006. While it would tow and serve as a chase vehicle, it was also designed to be more multi-purpose, serving as a daily driver, light-duty prerunner and some off-pavement exploring. Amazingly, that same vehicle is still in service, and has handled pretty much everything we have thrown at it.
If there has been one fly in the ointment affecting the versatility of our big Dodge, it is the cold hard fact that both of its axles carry open differentials. With both differentials open, traction was definitely limited, and at times we were hopelessly left spinning our tires as our open diffs fruitlessly sent power to whatever tire was spinning the most. On top of this, recovering a girthy 7,000 lb. truck from the muck is definitely not a fun endeavor. When we originally decided to rectify this situation way back toward the beginning of Project Heavy Metal’s life, there were very few solutions for the big AAM 11.5 axle besides the factory limited-slip. Wanting more traction, we decided to wait things out until other offerings came onto the market.
Thankfully that wait was worth it as ARB now offers the RD139 Air Locker for vehicles equipped with the AAM 11.5 axle. Most of our readers are familiar with the ARB Air Locker, but for those who are not it is a selectable locker that goes from an open differential to a spool with the flick of a switch. There is no mucking about waiting for enough slip to activate a limited-slip. Once engaged, it sends 100 percent of power to both wheels just like a spool would, but with the major advantage of being able to be shut off and returned to the pavement-friendly characteristics of an open differential.
Many ARB Air Lockers see service in the front, but ours would live in the rear and the reasons for this were fairly simple. Some automatic lockers (ones that activate by sensing wheel slip) can create somewhat strange handling dynamics as they lock and unlock. Towing heavy loads can also be less than ideal with an automatic locker as it can put large strains on internals. While a locked rear end can help plow through deep snow in a straight line, it can be downright scary on ice or while cornering in snow because of massive understeer.
In the end, going with the ARB Air Locker in the rear just makes our truck more versatile and that, for us, is why we built our truck in the first place. We won’t bore you with the step-by-step install, but follow along as the techs at 4 Wheel Parts’ Redondo Beach location put an ARB Air Locker in the rear of our Project Heavy Metal Dodge Cummins.
The first thing that strikes you about the ARB RD139 is its immense size. Designed to fit the 11.5-inch ring gear and withstand high-torque loads, it weighs in at a hefty 52 lbs. With a two-piece case manufactured from heavy cross-sectioned nodular iron, it is said to be virtually unbreakable (ARB’s computer modeling suggests it will handle up to five times more torque than the OEM differential). The two-piece design also allows for the side gears to be upgraded to fit 35-, 37- or 40-spline shafts. Like all Air Lockers, it features ARB’s patented Timed Gear Technology for the highest locking strength and split-second engagement. The RD139 fits 2003-2009 Dodge Ram 2500/3500 and 2000-2006 GM 2500/3500 trucks with the 11.5 AAM rear axle.
Originally we had equipped our Ram 3500 with 4.10 gears with the idea that we could cruise easily at high speed. While that held true, the big Dodge was just a bit lazy off the line (well as lazy as a truck with just over 800 lbs-ft of torque at the rear tires can be). Towing heavy loads (10,000 lbs. plus) also amplified this, as it seemed to take forever for the Cummins diesel engine to get into the boost from a dead stop. To solve this, we went with a new set of G2 Axle & Gear 4.56 gears. Designed to handle the extra loads from big tires and power, they are forged from 8320 steel, heat treated for durability and lapped for quiet operation. We didn’t expect that big of a difference, but were pleasantly surprised as the 4.56 gears definitely woke up our Ram and we saw a slight MPG increase to boot.
Another item that the techs at the 4Wheel Parts Redondo Beach store installed was G2’s massive new heavy-duty aluminum differential cover for the AAM 11.5. Available in either a raw aluminum finish or black powder coat, the stout cover is ribbed for increased rigidity and heat-treated. It is made in the USA and also features bearing cap support bolts along with a magnetic dipstick and drain plug. The huge size of the cover adds a lot of fluid capacity for additional cooling, and ours held 12 pints of gear oil!
Routing the air line on an ARB Air Locker is another critical step. Not enough slack can create problems, while too much may cause it to rub on internals. While ARBs need a bit more care during the installation process, the versatility they offer makes the bit of extra work well worth it.
Getting the right pattern on a gear set is absolutely critical and a process we gladly leave to the professionals. Once properly set up, the pattern should sit in the middle of the gear both horizontally and vertically.
One of the nice steps that the 4 Wheel Parts techs take is to use this handy tester. It pressurizes the line and the gauge allows an easy way to check that the Air Locker’s O-ring and fittings are sealed properly and holding air.
For such a big truck, our Ram 3500 has surprisingly little space under the hood. To fit the ARB CKMA12 high-performance air compressor that would supply the air to our Air Locker, the 4 Wheel Parts crew actually built a trick little bracket that mounts it just behind our front bumper. Besides activating the locker, the compressor can also fill up to four 37-inch tires in a single duty cycle.
ARB USA (425) 264-1391 www.arbusa.com
4 Wheel Parts Performance Center (Redondo Beach) (310) 973-6115 www.4wheelparts.com
G2 Axle & Gear (877) 852-7720 www.G2Axle.com