A locking differential that mechanically or electronically locks both wheels on an axle to spin together. Used in off-road and drag racing applications.
Locker (locking differential) is a differential type that completely locks the two wheels on the same axle to rotate together at the same speed. Unlike an open differential or LSD, a locker does not allow any speed difference between left and right wheels when engaged. This provides maximum traction in low-grip conditions but causes tire scrub during normal cornering.
Locker types include automatic (engages when slip is detected, like the Detroit Locker), manual (driver-engaged via switch or lever, common in 4x4 trucks), electronic (computer-controlled engagement, common in modern off-road vehicles like the Wrangler Rubicon), and air (ARB Air Lockers, popular in dedicated off-road builds). Each has different characteristics suited to different use cases.
Lockers are essential for serious off-road driving (rock crawling, deep mud, technical trails) where one wheel may lift off the ground. Without a locker (or with an open differential), all torque goes to the unloaded wheel, killing forward progress. Lockers are also used in drag racing where launch traction is critical. They are not typically used in road driving because they cause noticeable handling effects in corners.