The Detroit Locker was initially developed during World War II by Thorson. After the War, the company changed its name to Detroit Engineering and began marketing its locker to the aftermarket. Detroit Engineering became Tractech, Inc. and was purchased by Eaton Corporation in 2005.
Despite all the corporate shifts, the basic design has remained unchanged over the last five decades, upholding the theory that if it ain't broke, don't fix it. One of the legends surrounding Detroit Lockers is that they don't break, so fixing has never been an issue. One major advantage to Detroit Locker fans that comes with the company's absorption into a massive corporation like Eaton, is the availability of resources for testing and manufacturing.
Here is a real layman's definition of differentials. The "diff," as we gearheads refer to it, delivers torque to your wheels. With an open diff as used in conventional street vehicles, the torque takes the path of least resistance, ie: the wheel with the least load. Picture a vehicle making a 90-degree turn on pavement. The wheel to the inside of the turn carries lessweight and travels less distance than the wheel on the outside of the turn. The open diff channels the power to this inside wheel. If the power went to both rear tires equally while going around our 90-degree turn, the vehicle would "push" or try to go straight ahead.
Open axles are good for going around corners on the street. But sending the power to the tire with the least traction can become a problem when the terrain turns rough. This is where traction aiding diffs come into play.
First up, the ladder of traction aiding differentials is the limited slip, called "limited" for a very good reason. While this type of diff (common on light trucks), biases where the torque goes to an extent, (20% to 40% when new) in the end, it still ends up headed straight for the wheel with least resistance. So, if you're headed through a twisty, turny, rocky mess and one wheel ends up in the air - that will still be the one getting all the torque and you'll be dead in the ditch. Limited slips are adequate for light off-roading, or installed in the front axle of a 4x4 with a rear locker. But they are not suitable for getting you through the tough stuff.
Let's now look at locking differentials like the Detroit Locker and Eaton's stable of aftermarket lockers. As the name implies, they lock the axle so both wheels are dealt an equal torque hand. One wheel's airborne, no sweat - the other one has full traction and off you go. All of the following diffs are available through Eaton, either under the Eaton brand or as Detroit Locker. Starting with their limited slip, here they are:
The Eaton Posi Limited-Slip has the advantage of the brand's bulletproof reputation. Designed for traction control on the track, it may not be the ideal upgrade for hard-core enthusiasts. But, for light duty travel, it will get you through some rough patches. For example, the Forest Service issues specialized trail maps for SUVs, acknowledging that familyfocused 4x4s are driven by urbanites who need bunny slopes to hone their skills. The kind of "maintained" truck trail found on these maps, which features sandy shoulders and wind-blown, washboard surfaces, would be ideal Posi LSD terrain.
Within Eaton's general locking differential family, there are automatic and selectable versions, both are pretty self-explanatory. The Eaton ELocker electronic locking differential falls in the selectable category. With an ELocker, the vehicle has the same handling and traction characteristics as a conventional open axle. That is, until you push a dash-mounted button, allowing the axle to lock up and send full power to both wheels. This magic happens via electromagnetics that push locking pins into a sturdy collar. The collar locks an axle side gear into the differential case, creating a spoollike diff that can deliver equal power to both wheels. The precision-forged gears are designed to mesh perfectly for improved strength and durability over a standard cut gear. Since the unit is activated electronically, a simple electrical wire running to the diff is all that's needed to activate it. As testament to its functionality, the ELocker is standard equipment on the Hummer H2.
Unlike the Hummer ELocker however, the aftermarket ELocker has a 4-pinion, instead of a 2-pinion, carrier resulting in. a locker that's 70 percent stronger. This locker is available for Dana 30 and Dana 35 axles, the front axle configurations on many Jeeps. If what you're looking for is a rig that can scale sheer cliffs, or pull you out of waistdeep mud, the set-up is a 4x4 with an ELocker in the front axle and a Detroit Locker in the rear.
Regarding the latter unit, the Detroit Locker's traction performance is legendary. If you ask the hardcore players of the off-road world what kind of diffs they've got in their big, honkin' trucks, you'll probably get this pithy reply: "Detroit Lockers." Or, you might get a grunt like, "You idiot, what do you think I've got?" These are the guys who lead expeditions up and down mountain trails and then end up hauling out the flatlanders, the guys who were raised by wolves, who stalk fish in mountain streams and get to their destination no matter what. "Off-roading is all about strength," says Eaton's Michael Mulholland, "Detroit Lockers just don't break."
If the concept of automatic disengagement gives you pause, it shouldn't. There's no danger of the locker not disengaging on an asphalt curve or city turn lane. You couldn't disengage it yourself more accurately than the unit itself can. Case in point: Detroit Lockers are used on both the NASCAR Craftsman Truck Series and the Nextel NASCAR series where split seconds can make or break a team.
"The locker unlocks through the turns," explains Mulholland, "then locks back up to launch the vehicle out of the corners. Without a locking diff, the inside tire would spin coming off the turn." Race mechanics have the ability to finetune their differentials to lock up faster, depending on how the race truck or car is set up. But let's face it, who among us has a button or switch finger, or the feel of our vehicle, that would be more accurate or quicker than a NASCAR vehicle?
Locker can be found in the testing lab, the land of automotive sadists. "They put shock loads on differentials," says Mulholland, "then they repeat it 500,000 times in different temperature extremes. Our testing is done in the lab, not in the marketplace." While the thought of auto part abuse by guys in white lab coats may sound cool to some, the really critical part of the testing is done on Eaton's 600-acre proving grounds in Marshall, Michigan. The grounds are set up with the kinds of obstacle courses that would bring tears of joy to the eyes of most enthusiasts. A 20-percent grade is set up with rollers along a left-hand track. With a limited slip or open axle differential, the left wheel slips on the rollers, gets an overdose of power delivered to it and the vehicle ends up sitting at the bottom of the grade, spinning gaily. With a locked differential, the vehicle flies up the grade like a champ.
There's also a field of moguls resembling a double blackdiamond ski run, a rock run and twist ditch constructed to be approached from different angles - all designed to defy gravity and keep at least one wheel in the air at all times. Mulholland took a spin through the twist ditch in a two-wheel drive truck with a locker - he made it through, while a second truck, a 4x4 with a limited slip differential, got twisted into a pretzel and was left for the buzzards.
Just for good measure, Eaton's product-punishers also have a mud grade, 45- and 60-percent hill climbs, a rock crawl, a log walk, a sandpit and a swamp course as well. All this testing is performed just so we can take our own Eaton locker-equipped rigs and tackle the same conditions, just for the fun of it.
SOURCE:
Eaton Performance Products Division
www.eatonperformance.com
