A lunch box locker is a type of light duty automatic locker made for most Jeep, truck and SUV differentials. The lunch box locker is actually a slang term used to describe this type of locker because, like a lunch box, the outer packaging remains the same while the contents of the interior are changed. Metaphorically, the differential itself is the lunch box and the locker is the content within it.
Lunchbox lockers function like their full-size counterparts. They are designed to automatically couple and lock both wheels on an axle at the same time it detects that one wheel receives more torque than the other. This locking action applies 100% of the driving force to both wheels, essentially creating a spool. When the torque difference between each wheel is reduced, the locker can be unlocked and allow differentiation of the wheels, which is beneficial for maneuvering around corners.
The lunch box locker has its pros and cons.
The main advantages of these recessed lockers is that they are simple units that are designed to be installed on a factory open differential carrier (and sometimes even factory limited slip carriers). In most cases, it is not necessary to remove the carrier from the axle, which means that it is not necessary to reset the pinion and ring gears. In the few cases where it is necessary to remove the carrier, it is not yet necessary to reset the ring and pinion because the pinion is bolted to the carrier and as long as the carrier is reinstalled with the correct shims that were already in place, the ring and the pinion play will remain the same. This is very advantageous because the experience and tools required to set up a ring and pinion from scratch can quickly become expensive. If the time comes when you no longer want your lunch box locker, simply remove it and reinstall the stock differential parts and your differential will perform just as it did when it was new.
The main disadvantage is that they are only as strong as the bracket they are installed on. For vehicles with smaller axles, such as the Dana 30 and Dana 35, which are popular with the Jeep Wrangler and Cherokee lineup, this causes some limitations, primarily with the size of the tires. Using anything over 33 inches is not recommended with these small units, however there are many off-roaders who will testify that a lunchbox locker was able to turn 37-inch tires without incident. It largely depends on the type of driving that is done. Obviously, the more extreme the terrain and the larger the tires installed, the more likely you are to experience a failure.
In short, a lunch box locker is an ideal candidate for anyone venturing into a recreational off-roader. The traction they offer for their minimal price (mostly between $ 200 and $ 300) is a huge performance gain. A 2WD vehicle with a locker can perform almost as well as a 4WD vehicle with open differentials. Combine that with the fact that the home mechanic can install them with basic garage tools and you have a recipe for off-road fun.
