Installing an ARB diff lock, part 1


Once you've installed better tires, the number one modification you can do to a four-wheel-drive vehicle to improve traction is to add a differential locker. Lacking traction control or lockers, a four-wheel-drive vehicle is actually only a two-wheel-drive vehicle: In any situation in which one rear tire and one front tire lose traction, the mechanics of an open axle differential mean all the engine's power will be directed to the tires with no grip. Ironic but inevitable. Traction control, which uses the vehicle's anti-lock braking system to apply braking pressure to a spinning wheel, redirects power to the opposite wheel effectively. However, traction-control systems are reactive—they only start working once wheelspin is detected. A manual locker not only distributes torque equally to both tires (which traction control does not), it can also be used proactively, when the driver sees a difficult spot ahead. With just one differential locked, you have increased your available traction by fifty percent. Install a diff lock on a two-wheel-drive vehicle and you've doubled your traction. (See also the comments section on this post.)

Our 2012 Tacoma lacks traction control, and we did not get the TRD package, which includes a manual-locking rear differential. So we planned from the start to add one, and the ARB was a natural choice. 

Designed by an Australian engineer and four-wheel-drive enthusiast named Tony Roberts, the Roberts Differential was purchased by ARB in 1987. Originally made for the Toyota Land Cruiser, there are now over 100 applications in the ARB catalog. Needless to say it's been well-proven in the field.

The ARB requires an air source to operate, and ARB offers three compressors, from a basic model only suited for that purpose, to a twin-piston design capable of providing a large volume of air. We got the mid-range, single-piston, heavy-duty compressor, which can also inflate tires.

Since I'm a rank rookie on setting up differentials, we plan to have our master mechanic, Bill Lee of Bill's Toy Shop in Silver City, New Mexico, do that job with my assistance (meaning I'll take photos). Besides Roseann's nephew, Jake Beggy, Bill is the only other person we trust implicitly with our vehicles. In the meantime, I installed the compressor and operating switches, and ran the air line to the back axle.

I had to cut off the clip securing the wiring loom (just left of the bracket) to make room for the compressor's air filter.

There was exactly one spot in the engine bay of the Tacoma where the compressor would fit. Fortunately it was nearly ideal, and did not impede access to other components. I could have used self-tapping screws to secure its mounting bracket to the sheet metal there, and in all probability they would have been adequate. But I confess to a prejudice against those things—I wanted stainless-steel bolts and nuts. That meant undoing part of the plastic inner fender molding so I could worm one arm up inside the fender to blindly fit and hold a wrench to the nuts once I'd drilled the holes. Two hours of blasphemy and bruising ensued, but eventually it was accomplished.

The compressor in place, with the quick-release fitting for a tire-inflation hose on top. The black box to its right is the relay. I deemed a self-tapping screw sufficient for that.

The compressor's wiring loom comes in two parts, so there is minimal wiring to push through the firewall. Just four male wiring tabs needed to be pushed through a rubber grommet sealing off the truck's main wiring loom where it passes through to the cab. I taped the tabs to a fat nail normally used as a tent peg, and poked that through the rubber, which seemed to close up satisfactorily around the hole.

With those wires connected to the inside wiring loom, the next task was to mount the switches for the compressor and locker. This can be accomplished easily with the small auxiliary switch panel offered by ARB, which simply screws to the bottom of the dash, but I wanted something that looked a bit cleaner. Two blank switch holes on the left side of the dash offered themselves, and—after some judicious work with a Dremel (would it kill manufacturers to make these holes a universal size?), and some upside-down winkling to get the wires up there—the result was satisfactory.

Next stop: Silver City.