Mark Houlahan
Tech Editor, Mustang Monthly
December 21, 2010


We could argue that the ARB Air Locker is more of a spool than a locker, since it doesn't allow differentiation when engaged, but since it is called a locker by name and can be turned off, we placed it under the locker subheading. The ARB is made in Australia and uses compressed air to engage an internal tooth piston within the differential to lock the side gear to the case, which locks the axles together. Of course, this requires a small on-board air compressor or other air source for it to work. Originally designed for off-road use, the ARB Air Locker has gained traction (sorry) in the performance automotive aftermarket as an upgrade for serious street and drag race use. There is no differentiation, as the ARB acts like a spool when engaged. The differential housing is made of nodular iron and the internals are nickel alloy steel with aerospace coatings on the gears. With fewer moving parts, the ARB has a reputation on and off the road for strength. Unfortunately, it is only available for the 8.8-inch in 28- and 31-spline configurations, and for the 9-inch in 31- and 35-spline

We're putting the Auburn ECTED Max under lockers as well because it's one of the only differentials that we know of that can also be electronically controlled from a limited-slip state (off) to a full locker (on). It does this by way of an electro-magnet that creates a lateral movement within the gearcase, compressing the clutch pack and locking the side gears to the differential. The ECTED Max is manufactured from aircraft-quality 9310 heat-treated billet steel for optimum strength. Because it uses an electrical connection, the locker simply needs an electrical source routed to the axle housing. No air system or mechanical linkage is needed to engage it, plus it's quiet, with no ratcheting sound like typical lockers have. The ECTED Max is currently available for the 8.8-inch late-model axle only in both 28- and 31-spline configurations.

Our last locking differential we'll look at is the Yukon Gear Grizzly Locker. The Grizzly is a tough mechanical locking differential made with a forged steel differential case and 8620 triple alloy steel internals. Similar to other mechanical locking differentials, the Grizzly Locker uses a central pinion locked to the differential case that the axle side clutches engage with, giving optimum straight line traction, yet allowing differentiation in turning. The Grizzly Locker is available for both the 8-inch and 9-inch axles in 28- and 31-spline options, as well as a 35-spline version just for the 9-inch.

The grand daddy of lockers has got to be the Detroit Locker. Now owned by Eaton Corporation, the Detroit Locker (also called the Detroit No Spin in other applications) was offered by Ford in some of the baddest muscle cars of the '60s as an option to try and rein in the big-block power of the day. Today, the Detroit Locker is still a viable option for a brutally strong differential that locks both wheels for optimum traction, but is still livable on the street due to its ability to automatically unlock for wheel speed differentiation. The Detroit Locker works by using two spring-loaded, driven clutch assemblies (in place of spider gears) that are mated to a centrally located spider assembly. The spider is driven by the main case and ring gear assembly. This means as long as the vehicle is going straight, the driven clutches are mechanically locked to the central spider, as if the axles are welded together. When differentiation is required, the outside wheel, which has a farther distance to travel, disengages the driven clutch on that side of the axle, while the inboard driven clutch stays mechanically locked to the central spider. The disengagement is what gives the Detroit Locker its famous click-click-click when turning at low speeds. The Detroit Locker is available for the 9-inch in 28-, 31-, and 35-spline options, as well as for the late-model 8.8-inch axle in both 28- and 31-spline.

Another electro-mechanical, magnetically controlled locker is the Eaton ELocker from Eaton Corporation. The ELocker differs from the ECTED Max we mentioned previously in that instead of being a limited-slip-based unit when "off," the ELocker instead acts like a traditional open differential when not engaged. The open-style diff is much easier on driveline parts and is also better on fuel economy, but when you need the traction abilities of a locker it is simply a push of a button away. When activated, the electromagnet creates a magnetic pull on a drag plate, which activates a ramping mechanism. This ramp acts as a one way clutch that engages the side gear, locking it to the differential housing. This all happens in a near instantaneous state for full torque equally transmitted to both wheels. Like the ARB locker, when the ELocker is engaged there is no differentiation for cornering. It's either locked or it is open, making the ELocker more suitable for drag racing and serious street use than for corner carving. The Eaton ELocker is currently available for 31-spline 8.8-inch axle configurations.

The Powertrax No-Slip locker is offered by Richmond Gear for the 8-inch 28-spline; 8.8-inch in 28- and 31-spline; and the 9-inch in 28-, 31-, and 35-spline configurations. The Powertrax unit is a unique locker in that it is installed into the vehicle's original open or limited slip differential housing in place of the OE guts. What this means is that you can easily upgrade your 8-inch open rear in your driveway with basic handtools, without affecting ring and pinion mesh, bearing preload, or other sensitive measurements. The Powertrax is designed to lock both rear axles together for full torque output to both axles, no matter the traction surface, yet allow for axle speed differentiation via disengagement of the side clutch, similar to the Detroit Locker explained earlier. With no friction clutches to wear out, no special setup tools required, and installation that can be accomplished at home in a little more than an hour, the Powertrax No-Slip locker is a great choice for street use. If you're looking for an all out dragstrip option (or serious street) Powertrax does offer its original Lock-Right, which is stronger, but also noisier.


If all you care about is 100 percent traction and going straight, then a spool is a viable option for your ride. While not considered street friendly due to the harsh strain a spool can put on the drive-line parts of your car, limited street use is possible. Currie Enterprises offers a 9-inch lightweight full spool in 28-, 31-, 33-, 35-, and 40-spline configurations, while a mini-spool is also available for the 8- and 9-inch rear as well in 28- and 31-spline configurations. The mini-spool gets installed into a traditional open differential housing (inset), so it makes it a great way to install a spool without messing with gear mesh, bearings, and so on.

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Yukon offers both a mini and full spool for several Ford applications. The full spool is made from 4130 chrome-moly steel and is heat treated for strength. A standard spool is offered, as are lightweight race models to reduce rotating mass. The full spool for 9-inch axles is available in 28-, 31-, 33-, 35-, and 40-spline models as well as the 8.8-inch rear with 31-spline axles (requires C-clip eliminators or 9-inch bearing end conversion). Mini-spools are offered for the 8.8-inch axle with 28- and 31-spline axles, the 8-inch with 28-spline axles, and 9-inch with both 28- and 31-spline axles. The mini-spool can be easily installed into an OE open differential without disturbing ring and pinion mesh.