Project Double-Duty Ram: Lower Gearing & ARB Traction

The 1-Ton Cummins Gets Gears and a Locker

Some months back we took a bone-stock 2018 Ram 3500 Cummins pickup and began to transform it into a multipurpose rig. The owner uses the truck for both work duty and weekend play, so it has to be versatile. The plan was to build a crawler-hauler-daily-driver-working truck that can go reasonably fast in the desert, crawl a few rocks, and serve as a recovery and trailer-hauling rig.

The upgrades started with a complete Carli suspension system. The 3-inch Backcountry system used offers immensely improved off-road performance but with a much, much nicer highway ride. It included new front coil springs and full-replacement Deaver leaf packs, along with application-tuned Fox shocks with remote reservoirs. The stock 34-inch-tall tires were upgraded to 37X13.50R17LT Toyo Open Country R/T tires for improved traction and clearance. The truck is performing much better in the dirt but can still effectively tow heavy loads.

Next on the performance list was to change the axle gearing and install a front locker. The lower gearing will help offset the larger, heavier rolling rubber, and the locker will help the front axle pull fully with both front tires. We found all the parts needed with a quick trip to Summit Racing Equipment's website. We ordered front and rear 4.10:1 gearsets, installation kits, an ARB air locker and an air pump. Summit has always been our go-to source for any automotive part when we need it quickly because the company covers everything from crate engines to lockers and axleshafts to fasteners and everything in between. And its immense distribution network means there's never a huge wait. The parts arrived within a few days and our project was ready to move forward.

The axle work was all completed at Lamb Fab in Gilbert, Arizona. General teardown on both ends was similar. The diff covers were pulled to drain the fluid and axleshafts pulled to clear each differential. The carrier bearing caps were unbolted and the differentials pulled from each axlehousing. The pinion gear was unbolted and removed, and the pinion bearing race driven out of the axlehousing. On this truck both the front and rear differentials use threaded adjusters to set the carrier bearings.

We've shown you gear installs in the past, so we won't go through all the minute details of the installation. We'll hit on some highlights and specifics you may need to know for this particular installation. If you decide to do the work yourself, you'll need the usual gear-specific tools, and maybe a bit more.

There are a few noteworthy items concerning a gear install for this truck. First, a ring gear spacer is needed for the front ARB Air Locker. Also, the torque needed to loosen and tighten the rear pinion nut is quite significant. Lastly, you'll need a replacement inner seal for the front axle, and come up with a way to get the new one pressed into the axlehousing.

This 1-ton Ram truck came equipped with the Aisin six-speed transmission and 3.42:1 axle gears. With the swap up to 4.10 gearing, cruising rpm went from just over 1,400 to about 1,700 rpm, leaving the truck slightly overgeared compared to the stock configuration. But with more gearing to compensate for the taller, heavier wheel and tire combo, it means it tows and hauls like it's stock. This new gear ratio gets the bigger 37-inch tires rolling easier, and helps with acceleration and towing chores. The gear swaps netted us an average 2 mpg gain in mileage compared with running the 37s with the stock gears. The ARB is a proven choice for a locker and now allows judicious selective use of full-traction from the front axle when needed. This combo makes the truck better for both hauling and crawling.

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