Your Complete Guide To Lunchbox Lockers

If you have road-handling issues in your 4×4, you may have considered a lunchbox locker. This mechanism can aid road handling and maximize the performance of your vehicle. But, before you consider making some aftermarket changes, it is important that you understand how lunchbox lockers work and whether one is the right choice for your vehicle. 

The Lunchbox Lockers Basics

Lunchbox lockers are locking mechanisms designed to replace the spider gear set and fit into the stock diff carrier. The name “lunchbox” came about from the idea of packing up your lunch into a reusable box. You can use the same lunchbox every day, yet pack a different lunch. In this analogy, the stock carrier is your lunchbox. 


Lunchbox lockers replace the factory spider gears of the stock carrier. So, when you install a new lunchbox locker, you don’t need to bother resetting your backlash. In fact, you can install a lunchbox locker without removing the differential from your axle housing. This is far easier than many other lockers that require full disassembly and replacement of the entire carrier. 

Bearing in mind the ease of installation and the fact that lunchbox lockers require little to no maintenance, this is a great option for someone wanting to aftermarket upgrade their vehicle for as little as $200. 

How a Lunchbox Locker Works

A lunchbox locker operates in a similar way to a full carrier automatic locker. They have automatic locking differentials that are designed to automatically lock both wheels on the axle when reverse or forward torque is applied. This enables the vehicle to provide 100% power to the wheels, essentially creating a spool that connects the axle shafts solidly together. 

When there is no torque applied, the locker unlocks to permit differential variance in the wheel speeds as you negotiate a turn. 

In simple terms, the lunchbox locker splits power evenly between the wheels, regardless of which has traction. But, it needs to remain open during normal driving conditions to allow the proper operation of the differential. This is a significant improvement over standard open differentials that send all the power to the wheel that has the least traction. 

With a lunchbox locker, there is an oval-shaped hole where the center pin is located, rather than the circle on a standard diff. As torque is applied, the pin is forced to move a little, pushing the cam gears into the axle gears. This locks them together. When torque is no longer applied, the pin moves back to the center of the oval, ceasing to push on the cam gears. This then allows the cam gears to spin past the axle gears, creating that signature ratcheting noise of a lunchbox locker. 

The Pros and Cons of a Lunchbox Locker

There are different types of lockers on the market; each one works differently and has its own potential advantages and disadvantages. While lunchbox lockers are one of the most popular options, particularly when you’re on a budget, you need to be aware of the pros and cons before considering installation. 

The primary advantage of a drop-in lunchbox locker is that they are typically quite simple devices. They are designed to drop into a stock open carrier, but it may be possible to install one into a limited-slip carrier. 

The ring gear is connected to the carrier, and as the carrier is reused, generally, you don’t need to reset up the ring and pinion gears. This makes it far easier for DIY mechanics to install a new lunchbox locker. 

You can also remove the locker and reinstall the stock carrier if you want to revert back to an open carrier. 

However, no product is perfect, and the potential disadvantage of a lunchbox locker is that its strength is limited by the carrier, which can vary significantly. In fact, the strength of this type of device is usually less than a standard part, which means that you may encounter problems or damage after only a mild amount of abuse. 

Drop-in lockers are also prone to feelings of severe locking and unlocking compared to a full carrier locker. Fortunately, some manufacturers have acknowledged this and incorporate dampening mechanisms to create a smoother operation, reducing the harsh engagement and disengagement. 

Another drawback of a lunchbox locker or any automatic locking differential is that when they engage as you accelerate out of a turn or shift gears using a manual transmission, the transition from torque to no torque and back again can affect the performance. You need to be aware of how the locker affects vehicle handling. 

For example, during a turn, the outside axle spins faster than the inside access. This is the basic purpose of a differential. When torque is applied to an auto locker in the turn, it will engage, causing the vehicle to push straight or to the inside of the turn. This can create more unpredictable handling feel compared to an open differential. These characteristics are more noticeable in a smaller, lighter vehicle or one with a shorter wheelbase. 

Additionally, these handling characteristics will be more obvious if inclement weather has compromised the road traction. 

Most people who drive a vehicle with a lunchbox locker become accustomed to these handling characteristics, adjusting their driving style to accommodate them. However, there is a bit of a learning curve. 


Lunchbox lockers feature a simple design that keeps the costs low, but they can introduce road-handling issues. They are very easy to install and make a great option if you want cheap installation of a locker in your vehicle. 

While there are pros and cons to this type of device, they are quite cheap, and you can easily revert back to your standard carrier if you find you can’t get used to the new handling. 

If you are considering a lunchbox locker, it is a good idea to buy one for your front axle. This will allow your vehicle to be two-wheel drive on the road and almost eliminate any on-road handling issues, as the locker won’t randomly unlock and lock. 

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