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[wimp]

In case somebody is confused reading this thread. Eaton is the parent company who makes the brand, Detroit. Detroit has many products, two of which are the Detroit Locker and the Detroit Tru Trac. The Locker is fully locked until the amount of torque developed across the two half shafts is great enough to cause it to slip. This is good becasue you will spare your drivetrain parts of breaking. It also tends to disengage in high grip environments where both wheels are firmly planted on a grippy surface and the wheels experience different wheel speeds. ie while cornering hard on dry pavement or concrete.
Both the Locker and the Tru Trac have no air lines and are completely automatic. This is good becuaue they are always working and have no air lines which can rip off on the trail and render your truck less capable.
Full ARB air lockers or the E-Lockers are truly bad ass. When they are locked, they are locked, period. mis-using one of these types of lockers (like having no grip on a wheel and then suddenly getting grip all at once) is often fatal to drivetrain components. When used properly, there is almost nothing better!

I chose the Tru Trac front and rear. Cheap, easy to install, and I wasn't building a purpose built rock crawler. With them installed, my truck is worlds better off than the other rigs that have to "bump" their way over obstacles. Grip = fun!!!

The Detroit Tru Trac is very different than a Locker. Here is a clip of an article that I found which simply explains how it works.


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The gear types use gear friction/interference alone to achieve the same effect. The gears in a gear type limited slip look completely different from a clutch type. They have a bunch of smaller helical gears instead of the four or six bevel type gears found in open diffs or clutch type limited slips. The friction comes from the meshing of the many small gears inside the unit as well as the axial thrust of those gears into pockets in the housing. More torque wedges the gears even tighter into their pockets and creates more friction.

How much limited slip action a particular diff will generate is built in. That effect can be measured and is expressed as the bias ratio. Bias ratio describes how much torque the limited slip can shuttle from the lower grip to the higher grip tire. The rear Truetrac used for our TJ has a bias ratio of around 3.5:1. That means for every 100 pounds-feet of grip the low traction tire can support, the Truetrac can deliver up to 350 lbs./ft. to the high traction tire. That low traction side figure will include the built-in braking force of the limited slip as well as whatever grip the tire can deliver (there's always a little grip, unless the tire is in the air). That 3.5:1 ratio remains constant.

Trutrac bias ratios run from about 2:1 to up to about 5:1, depending on application. Like all gear type units, the Trutrac is well known for being smooth and predictable on the street because of the smooth actions of its gears verses the more grabby action of clutch type units. A clutch type limited slip is somewhat variable according to the amount of engine torque that's being fed into it... meaning it can have a lower or higher bias ratio according to throttle position. Trutracs are less responsive in that way and more linear in their performance. This is why many road racers use gear type LS units because the cars are more predictable powering out of a turn.

On the trail, the Trutrac responds very well to brake pedal modulation by the driver, especially in cases where there is a wide variation in traction side to side, such as a lifted tire. A little brake pedal application (or partial application of parking brake for rear units) will augment torque transfer by applying a little extra braking action on the slipping tire. This is the key to finessing a Truetrac for maximum performance.

A Trutrac would be a good choice for people who want seamless, automatic operation. It would be a fine overall choice for terrain where traction is relatively even side to side. It would be less advantageous for a hardcore rockcrawler that frequently experiences lifted tires and lots of weight transfer. With a driver who is clued in to brake pedal modulation however, the trail capability of a Truetrac equipped Rockcrawler could be well into the extreme category. You might want to read the older Hummer and military HUMVEE driving manuals, because those rigs use similar type differentials.