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Locking Differentials 101

Jeep Front Three Quarter
Ali Mansour
| Brand Manager, 4Wheel Drive & Sport Utility
Posted July 1, 2011
Photographers: Fred Williams

Traction Aid Basics

In the world of off-road performance products, the differential locker is near the top. A differential locker is mechanism that sits inside of or replaces the differential carrier. The job of a locker is to “lock” both axleshafts in unison so they can rotate at the same speed. Unlike an open differential carrier, which allows for different speeds of the tires as they move through different arcs of a turn and only sends power to the wheel with the least resistance, a locker splits the power between both wheels evenly.

On-road an open differential is rarely a problem, as both tires on the axle are firmly gripping the road. Even in light off-road situations an open differential works just fine—until one tire is in the air, on mud, or on another loose traction surface. That’s when the power goes to the tire that can spin, the one with the least amount of traction. Once that happens you are known as a “one-wheeler peeler” and you lose all progress.

But with a solid locker, no matter how twisted your rig gets and puts tires in the air or how slick a mud pit you are in, each tire continues to drive forward.

Though a set of differential lockers will greatly transform the off-road performance of your vehicle, not all are alike. And while some may increase your rig’s abilities off-road, that same locker set can create negative handling quirks on the street. Gathered here is a list of some of the most popular locking differential options and the pros and cons often associated with each.

Automatic (AKA Full-Time) Lockers
For a locker to be considered automatic, it simply means that the locker automatically engages when power (throttle) is applied, while operating like a conventional differential for going around corners. This is unlike a selectable locker, which requires an external actuating source. Probably the best known automatic locker is the Detroit Locker (www.eaton.com), a full carrier replacement locker that allows your wheels to change speed when making turns but that locks the shafts together once power is applied. Traditionally, automatic lockers such as the Detroit are some of the strongest and most preferred in vehicles that spend the majority of their time wheeling hardcore terrain.

Pros
• Strong and simple units with no wires, lines, or cables to tend with

• Once you become accustomed to driving with automatic lockers they can be barely detectable on the street

• Since the auto lockers allow differentiation (change in speed between the shafts) they often are a little easier to steer off-road

Cons
• Some have a reputation for loud bangs and pops, since the auto locker is constantly locking and unlocking as you drive

• Because of this, they can create strange handling characteristics that are especially noticeable in short-wheelbase vehicles.

• Generally not recommended for the front of vehicles equipped with fulltime hubs.

Drop-In (aka LunchBox) Lockers
Drop-in, or lunchbox, lockers are automatic lockers that sit in place of the spider gears found in an open differential carrier. No gear ratio or carrier change is usually needed to install drop-in lockers, provided the vehicle already has an open carrier and not a limited slip. These are usually very inexpensive lockers and are installer-friendly. One of the most common is the Lock-Right (www.richmondgear.com).

Pros
• Low cost

• Ease of installation

• Lightweight

Cons
• Can create noticeable handling quirks similar to full-carrier automatic lockers

• Can be noisy

The Gov-Loc
Found in the back of thousands of GM pickups, the Gov-Loc is a somewhat unconventional limited-slip/locker combo. The Gov-Loc received its name from how the mechanism works. As the differential begins to accelerate, a governor is thrust outward and up a slanted side gear. As the rpm increases, the governor forces pressure onto a thrust block, which allows a small cam gear to force the limited-slip clutches in place. The idea is that the faster the carrier rotates, the more the governor applies pressure, thus engaging (or locking) both shafts together. Yet while the design and theory behind it are solid, we rarely see them function consistently, nor would we place them in the category of an automatic locker.

Limited Slips Are Not Lockers
For all of the advancements in limited slips, they still cannot replace (or equal) a locker. Most limited slips, such as the Eaton TrueTrac (www.eaton.com) and the Auburn Gear Positraction (www.auburngear.com), use a gear or clutch engagement system to keep the wheels rotating at the same speed when power is applied. Though some are more aggressive than others and may seem to work similar to a locker in loose terrain, as soon as you enter extreme wheeling situations you find that the limited slip ultimately leaves you a one-wheel wonder like an open differential. This is mostly due to internal thresholds that keep the limited slips from completely “locking” up.

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