How you lock a differential depends on what type of locking differential your vehicle has. Selectable lockers give you a button or switch to engage manually, while automatic lockers do the work without any input from you. Both types force both wheels on an axle to spin at the same speed, giving you maximum traction when one wheel would otherwise spin freely.
Selectable Lockers: The Manual Process
Selectable locking differentials use electronic, pneumatic, or cable-actuated systems that you control from the cabin. The exact steps vary by vehicle and system, but the general process is straightforward.
For electronic lockers (common on trucks like the Chevrolet Silverado, Colorado ZR2, and similar factory-equipped vehicles), you press a button on the center console or dashboard. Some vehicles require you to hold the button for at least five seconds to engage both front and rear lockers. Your vehicle typically needs to be in a specific drive mode first. On Chevrolet models, for example, you need to be in Terrain Mode or have the transfer case set to 4Lo before both lockers will activate.
For pneumatic systems like the popular ARB Air Locker, the compressor activates as soon as you flip the switch, and the locker engages immediately. These systems are wired so the rear locker must be turned on before you can engage the front. This is a deliberate safety design: locking the rear axle first keeps the vehicle more predictable, since locking the front axle affects your steering.
Regardless of the system, you should engage selectable lockers while the vehicle is stopped or moving slowly in a straight line. This lets the internal components mesh cleanly. If the locker doesn’t engage right away, rolling forward a few feet usually allows the gears to align and lock together.
Speed Limits While Locked
Locked differentials are designed for low-speed use. Front lockers on many vehicles disengage automatically above roughly 15 mph. Rear lockers typically stay engaged at higher speeds, up to about 50 mph on some trucks when in an off-road drive mode, but this varies by manufacturer. Some owner’s manuals specify a maximum of 25 mph (40 km/h) with the differential locked.
These limits exist for good reason. When all wheels on an axle are forced to turn at exactly the same speed, the vehicle resists turning. At higher speeds on grippy surfaces, a locked differential can cause severe understeer, meaning the truck pushes straight ahead even when you turn the wheel. In the worst case, with both axles locked and good traction underfoot, the vehicle may barely steer at all.
Automatic Lockers: No Driver Input Needed
Automatic locking differentials, sometimes called “full-time lockers,” engage and disengage on their own based on wheel speed and traction. Brands like the Aussie Locker and Detroit Locker use internal ratcheting mechanisms or gear systems that lock the axle when both wheels are turning at the same speed (driving straight) and unlock the inside wheel when you turn a corner.
You don’t press anything to activate them. They’re always working. The tradeoff is a distinct clicking or ratcheting sound during turns, which is normal. One wheel needs to spin faster than the other when cornering, so the internal mechanism unlocks momentarily, producing a rhythmic click that some drivers compare to the sound of a playing card in bicycle spokes. If that clicking happens constantly while driving straight, it could signal a worn spring or a shimming issue inside the differential.
Where to Use a Locked Differential
Lock your differential when you’re dealing with low-traction surfaces: mud, sand, gravel, snow, ice, or uneven rocky terrain. These are situations where one wheel is likely to lose grip while the other still has traction. With an open (unlocked) differential, all the engine’s power goes to the wheel that’s spinning freely, which is exactly what you don’t want. Locking the differential forces power to both wheels equally, keeping you moving.
The key principle is to use it momentarily to get through a difficult section, then disengage once you’re back on stable ground. Drive slowly and in as straight a line as possible while the locker is engaged. Turning with a locked differential on a high-grip surface creates enormous stress on the axle and tires, a condition called “wind-up.” The tires fight against each other because the inside wheel is being forced to rotate at the same speed as the outside wheel, even though it needs to cover less distance in a turn. This can damage axle shafts, wheel bearings, and tire sidewalls over time.
Where Not to Use a Locked Differential
Never leave a selectable locker engaged on dry pavement or any high-traction surface. The differential exists specifically to allow the wheels to spin at different speeds during normal driving. Bypassing that function on a surface with good grip creates torsional forces the drivetrain isn’t designed to handle continuously. You’ll feel the vehicle resist turns, hear tire chirping, and risk premature bearing failure from the heat generated by the constant mechanical conflict.
Running mismatched tire sizes with a locked differential is especially dangerous. If tires on opposite ends of the axle are different diameters, one is always trying to turn faster than the other. With the differential locked, that speed difference has nowhere to go except into the axle components, rapidly increasing temperatures and wearing out bearings. Even small differences from uneven tire wear can cause problems over long distances with the locker engaged.
Quick Engagement Checklist
- Slow down or stop. Engage the locker at low speed or while stationary for the smoothest activation.
- Drive straight. Avoid turning the steering wheel while engaging. If the locker doesn’t click in, roll forward a few feet.
- Rear first, then front. If you have both axles equipped, lock the rear differential before the front.
- Stay slow. Keep your speed under 25 mph as a general rule, and well below that on technical terrain.
- Disengage on solid ground. As soon as you’re past the low-traction section, unlock the differential before returning to normal driving speeds or paved roads.