What’s the diff?

23rd December, 2020

What’s the diff?

Most four-wheel drive vehicles are equipped with a factory open differential in the front and rear. An open differential sends power to the tire that has the least traction and it also differentiates the speed of the tires when turning. This is perfect for on-road use but not so much for off-road use. When off-road, we encounter obstacles that may cause one or more of our tires to lose traction. When you’re stuck in this bind, you need the tire that has traction to spin in order to get you out of the sticky situation. This type of situation is when a locking differential is needed.

With so many options on the market, making your decision on the style that suits your vehicle can be tricky. Here we will explain the differences between the various options.

Limited-Slip Differentials

A common OEM option, a limited-slip differential (LSD) will sense when a tire is slipping and send more torque to the tire with better traction.  How much power is transferred is determined by how much traction is available to the slipping tire.  This means that an LSD is far more suitable for an application that has more equal traction from side to side than a situation where one tire is on solid ground and the other in mud or ice.

Automatic Lockers

Aftermarket automatic lockers remain engaged until one tire must go faster to navigate a corner.  As the differential senses the difference in wheel speed of the outside tire at the corner, the locker disconnects the outer axle shaft.  As wheel speed returns to equal, the unlocked axle shaft will lock up again.  They require traction to unlock.  If traction is insufficient and the axle is not able to unlock, the vehicle will severely understeer.   Auto lockers can be extremely noisy as they unlock.


A spool is a differential replacement that is locked 100% of the time.  Both tires will have power at all times.  This style cannot be disengaged which does not make it suitable for on-road use.  This option should only be used in off-road only vehicles.

Selectable Lockers

On the road, this locker remains an open differential. With the switch of a button or pull of cable, this locker will lock completely and send power to both tires, essentially turning it into a spool.  This is the most popular option because it is suitable for on and off-road driving.

ARB Air Lockers

ARB Air Lockers are completely selectable giving you the functionality of an open differential on-road but the traction off-road with the press of the button. ARB has a patented timed locking process that allows the locker to lock only in the strongest possible position.  This allows an increase in strength of up to 40%.  The ARB Air Locker is designed to be the strongest component in the axle assembly.

You may be thinking, why air? Air pressure allows for faster, firmer locker engagement.  This allows the ARB Air Locker to be engaged at nearly any speed as long as wheel speed is close to equal from side to side (no free spinning tires).  Many selectable lockers on the market require engagement speeds of less than 5MPH.  The air engagement also allows for faster disengagement   You’ll find that many other brands or factory selectable lockers are quite slow to disengage.

It is also very well known that lower air pressure in your tires provides a larger footprint for superior traction as well as a better ride.  To air down you need a way to air up and an on-board air system is a must-have item for the off road enthusiast. The ARB High-Output or Maximum-Output compressor will inflate your tires and engage your Air Lockers.  ARB Air Lockers have been on the trails in the US for over 30 years and are a trusted part for your off-road adventure.

Learn more about ARB Air Lockers.



Air Supply

At the flick of a dash-mounted switch, compressed air is delivered to the seal housing assembly via a nylon air line.

Air Supply

At the flick of a dash-mounted switch, compressed air is delivered to the seal housing assembly via a nylon air line.

Flange Cap Assembly

A billet-machined, alloy steel spider block supports the cross shafts, using the torque applied at each shaft to support the next shaft along.

Clutch Gear

ARB's patented locking system actually supports the side gear teeth, giving you more torque handling capability, exactly when you need it.

Bonded Seal

Steel reinforced, elastomer-bonded annular seal has been proven to handle 20,000+ cycles under the most extreme climatic temperatures on earth.

Two-Piece Design

Machining a case from two-pieces instead of three results in a much higher dimensional accuracy of the finished assembly and has allowed ARB Engineers to improve the design of other elements, resulting in a reduction of moving parts, increased strength and a more responsive activation.

Splined Side Gear

High-grade surface treatments, forged nickel alloy steel and ARB's patented timed locking system make this the most ‘lockable’ gear in the industry.

Wave Spring

Instead of a complex external actuator system to engage/disengage the lock, ARB Air Lockers® use up to 12 return springs to support the entire profile of the locking gear for a fast, positive and independent disengagement.

Spider Block

A billet-machined, alloy steel spider block supports the cross shafts, using the torque applied at each shaft to support the next shaft along.

Pinion Gear

Combining the strength of forged nickel alloy steel with redefined gear-tooth geometry, ARB has revolutionized locking differential gear design to yield structural advantages of up to 30% over commercially available high strength gears.

Cross Shaft Retaining Pin

Custom made, one-piece hardened retaining pins lock into the assembly using a tapered thread junction.

Forged Gears

With phenomenal forces being applied to the side and pinion gears within the differential, ARB has invested heavily in the application of forged gears, typically found in heavy-duty commercial, race and agricultural transmissions.

Diff Case

Fully machined, one-piece nodular iron diff carrier case offers the rigidy of a one-piece factory differential with twice the standard number of pinion gears to cope with the torque.

Long Cross Shaft

Alloy steels and performance surface technology make for a high-pressure running fit that can handle an enormous amount of punishment.