Locker and spool systems are ideally suited for racing and special applications, and in most cases, they can be unnecessary or dangerous for the street. Lockers can handle tons of horsepower into the 1,000-plus range, but most LSDs are maxed out by the time you hit 600 hp. Four-wheel-drive off-road trucks are special-application vehicles and often need constant traction over a variety of terrain. Therefore, many owners use lockers rather than LSD units for off-roading. However, lockers do present some issues on the street because they make a fair amount of noise when turning corners.
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Spools, which are not differentials, connect the axles together directly so that they always spin at the same rate. As a result, vehicles with spools struggle to corner effectively and should not be used on the street.
Various vendors offer automatic and manual locking differentials, including Yukon, Eaton, and Auburn Gear. Auto lockers operate similarly to an LSD. When torque is applied to the spider gears, the unit instantly locks the axles together and you get solid lock-up with no slipping. Manual lockers only lock the axles together when told to, via a button on the dash. Manual lockers are either electronic or pneumatic.
A locking differential locks both axles together when torque is applied, ensuring both wheels spin regardless of traction, sending the same power to both wheels, all the time, under power. The automatic lockers open the coupling when the driveshaft applies little to no torque to the differential. In cruising or low-speed cornering, no power is applied. As soon as the driver accelerates and torque is applied to the differential, the differential locks. This can cause some handling issues, such as a side-ways jerk as the locker engages. Auto lockers are very streetable, but they take some getting used to.
An auto locker requires the driver to either adapt his or her driving style or simply live with erratic handling. Manual-transmission cars place different torque loads on the axle assembly than automatics. When a manual transmission applies torque and it is released with every shift, the differential locks and releases. As a result, you get more clunking and banging. As you accelerate out of a corner, the locker freewheels like an open differential until you hit the gas, applying torque; then the locker couples. This places the suspension under different loads and causes erratic handling, so the car can go into oversteer or understeer condition, which may be difficult for the driver to handle. These characteristics are even more pronounced in wet and snow/ice conditions.
The vehicle application determines whether you need to use a locker. Most street cars simply don’t need one. A well-built LSD unit provides the traction needed for street use and works great on the dragstrip or road course as well.
Power handling is big factor for needing a locker. Clutch-type LSDs simply can’t handle much more than 450 hp. If you run drag radials or slicks on the track, the tires will provide better traction than street tires and place more of a load on the differential. Then they will fail with even less power. There just isn’t enough clutch material and spring pressure to command lock up. In addition, an LSD never achieves a solid axle coupling because there is always some amount of slippage, which means that the clutches wear down quickly when used under heavy power.
A locker does not contain any clutches, so there is nothing to wear out. All lockers operate in a similar fashion. The axles are always coupled together, but a lack of torque allows the axles to spin faster than the main carrier. When a locker operates properly, neither axle can spin slower than the main carrier itself, which is unlike an LSD or open differential. Each axle can, however, spin faster than the carrier, such as the inner wheel in a corner.
Automatic lockers employ different systems to achieve both lock up and release. The most common is the spring type. Eaton pioneered the automatic locker system with its Detroit Locker. With this differential, the axles are coupled together at all times. However, when there is little to no torque application, the springs on the side of the coupling gears relax and separate enough for them to ratchet tooth to tooth. During a turn, this permits the inner wheel to spin faster than the main carrier, reducing tire chirp. As soon as torque is applied, the springs tighten and the coupling gears snap together.
Mechanical Locking Differentials
Other locking differentials feature flyweight designs, such as the Eaton’s mechanical locking differential, the MLocker, also known as a gov-lock. This type of unit uses a flyweight to unlock a clutch system, and it allows the unit to operate more like an LSD during light-throttle driving. When one wheel needs to spin with a speed difference of 100 rpm or more, the flyweight stops, engages the clutches that allow a cam to ramp the side gear, which, in turn, increases pressure on the clutches until the wheels are fully locked. When the differential RPM decreases, the unit returns to unlocked operation. General Motors installed the Eaton G80 gov-lock on many Chevy 4×4 trucks with 10- and 14-bolt rear differentials.
Gov-lock differentials function as they were designed, but durability has been an issue. Although they handle light street duty, they can explode under extreme or racing use. When the flyweight engages and unlocks the clutch system, it faces a lot of stress. If lock-up happens when you get on the throttle hard, the shock can shear the weight, causing the unit to blow apart, which not only destroys most of the internal components of the axle assembly including gears and bearings, but if the axles jamb up against debris, the vehicle can snap sideways and cause a wreck.
You can remove the flyweight and add shims to modify the gov-lock to tighten the cams and clutches. However, it’s not a reliable fix for a locking differential, and the gov-lock should not be used in high-performance applications. By the time you get into modifying the G80 differential, you could have a proper LSD or locking differential installed and get the real performance that you need.
Electronic Locking Differentials
These differentials provide the best of both worlds. The open and locked differential is durable and reliable and gives you complete control for its application. They are expensive to purchase and require advanced installation. Selectable and on-command lockers, such as the Eaton ELocker and the ARB Airlocker, use a lever and pneumatic or electric solenoids in the housing to engage the locking mechanism. These dual-type differentials have open-action and locked modes. They eliminate the harshness on the street in open configuration, but at the push of a button, the differential locks and puts full power to the tires regardless of traction. With more function comes more labor on the install side and more cost.
On-command lockers are typically air-, cable-, or electric-solenoid operated, which means you need to run wires and hoses to the differential. The cost is higher for these units, as there are more moving parts and functions to coordinate to make them work. The Eaton ELocker uses 12-volt power to activate an electro-magnetic field that forces the internal collars to move, locking the axles together. Because it is a simple wired application, the installation is much easier than an air- or cable-operated locker.
On-command locker main components are case, flange cap, side gears, pinion or spider gears, clutch gear, spider block, cross shaft, and return springs. The case or the housing holds the ring, pinion, and all other components. The flange cap is the stationary side of the locker, and it operates the locking mechanism. Side gears, similar to an open or LSD unit, connect to the axles and have locking cogs that lock into the clutch gear.
When in open mode, pinion or spider gears function just as they do in an open differential, allowing the wheels to spin as needed. Once the unit is locked, the pinion gears don’t move. The clutch gear is the locking gear. When the locker is engaged, the side gears are locked to the case through the clutch gear and this couples both axles together, applying full torque to both wheels. The spider block and cross shafts hold the pinion gears together to operate the unit in open-action mode.
Return springs provide stability for the engage/disengage process for the unit by pushing components together or apart, depending on the configuration of the unit.
The three ways to connect an on-command locker to the driver are lever, air, or electric.
Lever-actuated units are connected to the axle assembly housing through a cable system. A fork inside the housing cover rides on the locker. When the cable is pulled, the fork actuates the locker and either engages or disengages the unit. These can be fairly complex to install. For off-road vehicles, the cables can snag on trail debris.
Air lockers can be set up in two ways. They use either an air cylinder to operate the engagement fork, or actual air going into the car and directly into the differential. This involves drilling into the case and one of the bearing end caps that holds the carrier to the housing. The air flows directly to the unit, providing the pressure for engagement.
Eaton ELockers are electronically controlled through a 12-volt switch that operates an internal solenoid inside the carrier. The unit is wired through the case of the axle assembly housing, and the solenoid has a floating ring that slides between the case and the outer carrier bearing. This allows the wire to stay in one place; the circuit is completed through a Torrington bearing. When 12 volts are applied to the solenoid, the locking mechanism is engaged, fully locking the axles together.
Drop-in lockers are also referred to as “Lunchbox Lockers.” They are a budget alternative to a full-on locking carrier. A drop-in unit is an affordable method to couple the axles together while retaining differential action in turns. When one axle needs to spin at a different rate, the unit separates with a ratcheting action much like a full-size locking differential. The difference is that drop-in lockers are very loud; the ratcheting mechanism makes a lot of noise because of the way it works. Some drop-ins have internal dampening springs to help reduce the noise of the ratcheting process.
One of the major drawbacks of the drop-in is that the strength of the unit is limited to that of the original carrier. If the case is not up to the task, it can distort or break. Drop-ins are fairly capable by themselves; the case usually fails before the drop-in unit does.
Many companies build drop-ins, including Powertrax Lock-Right (made by Richmond Gear), Spartan by Yukon Gear, and Auburn Gear Max Locker. All work on the same basic principle with a few design differences, specifically in the way the spring and locking pin operate. The Lock-Right unit is the only dual-spring drop-in locker, which means it generally has a longer life. The other units are single-spring designs. Some come with new center shafts to hold the unit in the carrier. Spartan lockers do not require side shims, whereas the others do.
Drop-in lockers are good for rock crawlers and moderate off-road vehicles where the expense of a full locker is prohibitive and the power and weight of the vehicle is less, such as Jeeps and small trucks, although you can buy them for just about any axle assembly. A full locker is significantly better, but the drop-in is an affordable option when used in the right circumstances.
Spools offer a permanent locking axle, and it’s a durable and inexpensive system. Installation is simple and it’s lightweight. Nothing is stronger than a spool, but it has poor street manners. The tied axles do not allow the inside rear wheel to spin at a slower rate than the outside wheel.
Spools take the place of the differential and are an excellent, cost-friendly option for a strip-only car. Because the axles are permanently tied together, they spin when the ring gear spins, regardless of anything else. They are cheap, easy to install, and maintenance-free. Another key benefit is weight; a spool weighs only a few pounds while a locker can weight 25 to 30 pounds. That added rotating mass eats up power, so dropping 20 to 25 pounds from the drivetrain could mean the difference between a win and a loss.
The issue comes when trying to make a corner. A spool spins both tires at the same speed, so it makes the inside tire chirp and squeal. That may not be a huge factor if you rarely drive the car on the street, but big tires, a spool, and turns don’t mix very well. Most folks who have tried it become tired of it very quickly. Leave the spools on the strip.
Mini and full-weight spools are available. Mini spools are not really suitable for serious drag racing, as they are limited in strength by the stock carrier and crosspin. Mini spools are frequently used on circle track cars. Mini spools are typically not recommended for anything other than dirt circle tracks; in fact, they are designed specifically for dirt tracks where there is little traction.
Full spools are offered in two versions: regular and lightened. Weight is always a consideration when building a drag racing car, so saving every bit of weight possible is beneficial.
A lightened or “ultra-light” spool typically has extra holes drilled in the ring gear mounting pad and inner hub. Some spools have scalloped ring gear pads to further minimize weight. Some ultra-light spools are made from aluminum but these are not suited for high-powered cars; anything beyond 1,000 hp is just too much for an aluminum spool.
Weighing about half of a steel spool, the ring gear support simply cannot withstand much torque. All-aluminum spools must be replaced eventually because they wear out, while a steel spool does not. In fact, most aluminum spools have a limited warranty; most pro steel spools carry a lifetime warranty. Most pro-level spools are made from hardened steel, which reduces deflection and increases strength. Pro spools require either a 3.25- or 3.812-inch bore case. Another big advantage of the pro spool is the ability to run larger axles.
Written by Jeferson Bryant and Posted with Permission of CarTechBooks