Driving with an open differential off road is like piloting a Ferrari around an icy race track. Sure, you can get where you're going with a bit of driving skill, but you're missing out on the true performance potential of the vehicle. An open differential is a differential carrier that is fitted with a set of free-flowing spider gears. When throttle is applied the open differential sends power to the wheel with the least amount of resistance, which usually equates to the tire with the least amount of traction.
To upgrade from this open setup and have both wheels rotate at the same speed, your rig needs a differential locker. A locker works by "locking" the vehicle's differential (the part that rotates the axleshafts). A locked differential forces both wheels to rotate at the same speed. This allows both wheels to bite for traction and helps keep you moving in loose and challenging terrain.
Though there are a quite a few locking differential options available from the aftermarket, the drop-in, or lunchbox, style is by far the cheapest and most installer-friendly. Lunchbox or drop-in lockers, such as the mini-spool and Lock-Right, work by simply taking the place of the spider gears that are found in the open differential carrier. This means no gear ratio or carrier change is necessary to install the lockers, provided the vehicle already has an open carrier and not a limited slip.
To get a better insight into how the pint-sized traction aids work, we ordered up a Yukon Gear mini-spool and a Richmond Gear Lock-Right from the drivetrain specialist at Randy's Ring & Pinion. While these little lockers are not without their faults, they are simply some of the best bang-for-your-buck traction aids on the market.