What is a locker?


From the ExtremeTerrain Tech Articles

“Locker” in this instance doesn’t refer to the metal box used to hold school books and the occasional freshman. A locker for our purposes refers to a locking differential, which is handy to have when traveling over rough terrain. In order to explain why a locking differential is useful, we first need to establish what the differential is and why we need one.


Toy cars have a single piece of metal or plastic which serves as an axle between two tires. If the car is going in a straight line, this works well. When a car turns, though, the outer wheel wants to travel faster than the inner wheel. If your wheels are locked together during a turn, you will lose traction, wear out your tires and experience handling problems. This is annoying enough with a Tonka Truck; no one wants to do that in a real car at 60 mph with oncoming traffic. This is the reason cars have differentials. A differential is a gearbox on the axle which allows the wheels at either end of an axle to rotate at different speeds.

Most cars have open differentials, which work best when the tires have about the same amount of traction. When you turn the car, the traction on the inner wheel increases and the torque travels through the differential along the path of least resistance, which is the wheel with the least traction. This is helpful when going around a corner on pavement, as the outside tire, which has the least traction, is able to go faster. However, on unpaved roads, it can lead to one tire spinning madly in mud while the tires which have some traction are sitting still.

A locking differential, or locker, could take care of that problem. It “locks” the two sides of the axle together. In this way, the differential forces the wheels to turn at the same rate, regardless of which one has traction at the moment. When you are negotiating very rough terrain, a locking mechanism will make the difference between moving forward and just spinning.

Naturally, you won’t want to keep the differential locked, because then you’re back to driving a Tonka Truck. The whole point of a locker is that it gives you the ability to either lock the wheels together or leave them unlocked, as with an open differential. Lockers can be either automatic lockers, which lock themselves under certain conditions, or on-demand lockers which are completely driver-controlled.

Written by Andrew

"You're telling me it's got four wheels, two seats and goes faster than the speed limit? Good, I'm driving."

7 comments

  1. I would think that on-demand-lockers would require a great deal of understanding about when to use or release the lock. I’m sure I would go with the automatic and let the conditions dictate control. Thanks for the explanation, it really made sense and I’m not very mechanically inclined.

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  2. I’ve heard the term differential but would have been hard pressed to explain what it is. That’s one of the things I really like about your site. It’s informative and doesn’t leave you hanging about what terms mean. I’m not mechanical minded but I do like to understand what my mechanic is talking about.

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  3. I am the mechanic! While I do understand the parts and their functions I don’t know every little thing about every little part. I have learned a great deal about Jeeps since finding your site. I don’t usually work on them, but I’m learning, since I just bought one.

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  4. TMI for me! If I get in and it doesn’t start, I call for help. If it sounds funny, I call for help. I know how to drive it, but I don’t claim to know the first thing about how it works or what it takes to work. That’s why I pay the guy at the garage the big bucks.

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  5. OK, I read the article and I sort of get the gist, but I hope there’s no test! I think some guys are mechanically inclined and some are not. I definitely fall in the not category.

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  6. Got it! Now, what am I supposed to do with it? Hopefully there won’t be a test. lol. I Change tires and oil and occasionally a hose or belt but that’s the extent of my upkeep duties. I’ve often been tempted to take some automotive classes at the local college so I can work on my Jeep myself, but I really don’t have the time to do either. When I do get some spare time I want to get that Jeep off road and keep it there, without wasting valuable time working on it.

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  7. Now, if I would have read this one first, I would have been prepared for the next one. It never occurred to me that I should read these from the oldest to the newest. Reminds me of my accounting class when I learned about LIFO and FIFO. In this case it would be last in, first out as opposed to first in, first out! Whoa, it’s getting deep in here!

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