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.
The Lock-Right falls into...
The Lock-Right falls into the automatic locker category. Automatic lockers allow the tires to rotate at different speeds when coasting or turning around corners. When power is applied they automatically lock and unify the axleshafts' speed.
Spring-loaded slide pins are...
Spring-loaded slide pins are what allow the Lock-Right to ratchet and the side gears to rotate without engaging. This also gives the Lock-Right its notorious clicking sound when pulling into parking spots and making sharp turns on the road.
Mini-spools like this one...
Mini-spools like this one from Yukon are fulltime lockers that don't allow any slip or change in speed between tires. They are by far the most inexpensive way to upgrade to a locker, but are tough on your equipment and recommended more for dedicated off-road vehicles. We recommend using mini-spools for the rear only, as a fulltime locker makes steering extremely difficult over high-traction surfaces.
Both of the lunchbox lockers...
Both of the lunchbox lockers reuse the carrier's center pin, which is what unifies the carrier assembly. If your pin looks damaged or pitted be sure to replace it.
Both drop-in locker styles...
Both drop-in locker styles require the use of an open differential carrier. A standard open carrier uses spider gears to allow the axleshafts to rotate freely and at different speeds. While replacing the carrier isn't required, it is important that you inspect your carrier carefully to make sure it does not have any cracks or preexisting damage.
Rear axle assemblies like...
Rear axle assemblies like the Dana 35 and Chrysler 91/4 use C-clips to retain the axleshafts. If your rig is equipped with a C-clip-style rear axle, the Lock-Right drop-in locker is what you'll need, as the mini-spool does not have a provision for the C-clip axle retainer.