Driving your 4WD over uneven ground is one way of causing “wheel slip”. Wheel slip is the loss of traction that happens when one front and one rear tire lose contact with the ground. The result is a stuck vehicle. The ungrounded tires spin freely while the grounded tires do nothing.

The differential is the reason for this. Under normal driving conditions, the differential transmits the same power to both wheels yet when turning a corner allows them to rotate at different speeds. An internal unit of side and/or spider gears allow this.

The only way to fix this traction loss is to “lock” these gears together which in turn forces both tires to rotate in sync. The way you lock the gears is with a limited slip differential (sometimes called an LSD) but more commonly known as a locking differential or locker for short. Many types of LSDs available in the marketplace. The aim of this article is to explain their differences.

Spools

A spool is not technically a locker, but its ultimate purpose is to function as one. A spool is a unit that replaces the differential’s side and spider gears essentially creating a solid axle. This forces both tires to always spin at the same rate. The advantage of this is guaranteed traction, but it comes at the expense of premature tire wear if the vehicle spends most of its time on pavement because one tire will always “skid” when turning sharp corners.

It’s also important to make sure each tire has equal air pressure or they will wear down unevenly and cause a loss in fuel economy. A spool is not typically recommended unless the vehicle will spend the majority of its life driving off-road where traction is essential (especially for rock crawling, mud, and steep hills). A spool is the least expensive way to professionally lock the axle.

Trac Locs and Limited Slips

These are units that utilize a series of clutches that engage against the side gears. When one tire loses traction and begins to spin faster than the other, the clutches engage on the non-moving axle shaft and equalize the torque applied to both shafts therefore restoring traction. These types of LSDs work great on the street or for getting out of mud.

Their downfall is that they need to spin very fast for the clutches to engage. This will eventually cause the clutch plates to wear out and require replacing. In addition, they typically require a special lubricant for the clutches. Popular products in this line are the Detroit Tru Trac, Eaton Posi, and Auburn Limited Slip.

Light-duty and Heavy-duty Lockers

Heavy and light-duty lockers are almost always the preferred choice over clutch-type LSDs for off-road driving. Just like the units discussed above, these also replace the side and spider gears, but they’re replaced with dog-toothed ratcheting gears. This allows for manageable street driveability while offering superb off-road performance. These units provides a tolerable medium for drivers that do the majority of their driving on streets, but still want a locking differential. These types of lockers offer exceptional performance for their price, and are without a doubt the most popular type of locker used for off-roading for that reason. Popular products in this line are the Detroit Locker and E-Z Locker by Tractech and the Lock-Right and No-Slip by Powertrax.

Air Lockers, Electric Lockers, and Manual Lockers

These are the most advanced types of LSDs because offer both the comfort of an open differential with the ability to fully lock at the driver’s control. Air lockers utilize compressed air to lock the gears, electric lockers use an electric solenoid, and a third kind uses a cable for engagement. These types of LSDs are the most expensive, however consumers should be advised that they get what they pay for. They offer superb performance in any situation whether on-road or off. Popular products in this line are the ARB Air Locker, Eaton E-Locker, Auburn ECTED, and OX Locker.

A locker is one of the best 4×4 parts you can install on your vehicle. The traction they provide when compared to standard open differentials is incredible and will open new roads for your off-road adventures.

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