locking differential is designed to overcome the chief limitation of a
standard open differential by essentially "locking" both wheels on an
axle together as if on a common shaft while still allowing them to
rotate at different speeds when it is required (such as when negotiating
a turn). This forces both wheels to turn in unison, regardless of the
traction (or lack thereof) available to either wheel individually. An
open differential will cease the transmission of torque to one wheel if
the opposite wheel has little or no traction. This may occur if one
wheel comes into contact with mud, snow, or ice, or if the wheel is
somehow removed from contact with the road after encountering an
obstacle or area of soft ground. In such a situation, an open
differential will continue to spin the wheel with the least amount of
traction but will transmit little or no power to the wheel that has more
solid traction. Basically, it will transmit only as much torque to both
wheels as the wheel with the least amount of traction can sustain. This
can result in the vehicle failing to deliver enough torque to the drive
wheels to keep the vehicle moving forward, at which point it will be
stuck. A locking differential solves this problem with its capability of
delivering 100% of available torque to the wheel with the most traction.
Types of Locking Differentials
There are two main types of lockers: automatic and selectable.
lockers lock and unlock automatically with no direct input from the
driver. Some automatic locking differential designs ensure that engine
power is always transmitted to both wheels, regardless of traction
conditions, and will "unlock" only when one wheel is required to spin
faster than the other during cornering. They will never allow either
wheel to spin slower than the differential carrier or axle as a whole.
The most common example of this type would be the famous "Detroit
Locker," also known as the "Detroit No-Spin," although there are many
others. Other automatic lockers operate as an "open," or unlocked
differential until wheelspin is encountered and then they lockup. This
style generally uses some type of internal governor to sense a
difference in wheel speeds, or they react to torque input from the
driveshaft. An example of this would be GM's "Gov-Lok." This is the type
most often found on vehicles factory equipped with a locking
A "selectable" locker allows the driver to lock and
unlock the differential at will from the driver's seat. This can be
accomplished via compressed air (pneumatics) like ARB's "Air Locker,"
electronic solenoids (electromagnetics) like Eaton's "ELocker," or some
type of cable operated mechanism as is employed on the "Ox Locker." This
allows the differential to perform as an "open" differential for
improved drivability, maneuverability, and reduced tire wear, while also
having full locking capability for ultimate traction when it is
desirable or needed. This is really the best of both worlds, but
selectable lockers are more complex, and therefore more expensive, than
their automatic counterparts. Some people also feel that this added
complexity reduces their overall strength and durability and requires
increased maintenance over the long run.
Locking differentials do have some disadvantages. Because they do not
operate as smoothly as standard differentials, they are often responsible
for increased tire wear. Some locking differentials are known for making a
clicking or banging noise when locking and unlocking as the vehicle
negotiates turns. This is annoying to many drivers. Also, some locking
differentials can affect the ability of a vehicle to steer in some
situations, especially when the locker is located in the front axle. They
are also capable of subjecting the axle shafts to much higher torque loads
than would be possible with an open differential because they allow 100%
of the available torque to carried by a single axle shaft as opposed to
being divided up between the two. Under extreme conditions, this can cause
an axle shaft failure.
Except for the added stress on axle shafts, these disadvantages primarily
apply to automatic lockers, and can be mitigated, to some degree, by
proper maintenance and setup. Tire wear can be minimized by ensuring that
the tires are properly sized and inflated. Steering difficulties can be
mostly eliminated by selecting modern lockers which are better engineered
than earlier versions which were notorious for steering difficulties.
Driving habits, vehicle weight, and tire size can also have an effect on
the behavior of a locker.
Limited slip differentials are considered a compromise between a standard
differential and a locking differential because they operate more
smoothly, and they do direct some amount of torque to the wheel with the
most traction, but they are not capable of 100% lockup.
Applications for Locking
Four wheel drive vehicles that drive off-road often use
locking differentials to prevent from getting stuck when driving on loose,
muddy, or rocky terrain. Locking differentials are considered essential
equipment for serious off-road driving.
Race cars often use locking differentials in order to
maintain traction during high speed maneuvers or when accelerating at
Some utility vehicles such as tow trucks, forklifts,
tractors, and heavy equipment use locking differentials to maintain
traction, especially when driving on soft, muddy, or uneven surfaces.
Lockers are common in agricultural equipment and military trucks.
Other sources of Locking Differential information:
Differential Differences - Types of
Detroit Locker -
Locker - About ARB Air Lockers
How the ARB Air Locker
Ox Locker - About OX Lockers
How the OX Locker Works
ARB Air Locker Installation
Locker Compressor Wiring Diagrams
Lunchbox Lockers - What is a Lunchbox Locker?
What are Lincoln Locker & Fozzy Lockers?