Detroit Locker*
Overview: The Detroit Locker is an automatic locker that uses heavy springs and geared teeth to allow the outside wheel to spin faster when turning. In most applications the Detroit Locker is a replacement case, but some-such as for the GM 14-bolt, Dana 70, and Rockwell axles-it drops into the stock carrier. We like them for front applications best but have used them in the rear of longer-wheelbase vehicles with much success.
Street:*
Keep in mind we've tested Detroits in short- and long-wheelbase vehicles. In a longer vehicle, the handling drawbacks aren't as bad, but the short stuff (like Wranglers) earns this locker a bad on-road score. Whether you're turning or going straight, if you're on the gas, a Detroit Locker behaves just like a spool.
When you let off the gas, the Detroit will unlock. This is especially noticeable in a rear application of a high-horsepower, manual-transmission, short-wheelbase vehicle-such as a V-8 Jeep-and the resulting loading and unloading can cause a violent jerking that you need to get used to. We've driven rigs with super-supple suspensions or no sway bar that have changed lanes from the action.
Off-road:****
A Detroit Locker is a really strong differential, and about the only way we've seen them break is when they're violently loaded and unloaded-like when an axleshaft breaks. This vulnerability is the only reason the Detroit loses one point in the judgment. While you can lose some ability to turn when used in a front application, we've had little trouble snaking through tight spots by modulating the gas pedal to allow the front differential to unlock periodically for tighter turning. We like the no-brain traction with no buttons to push or levers to pull.
Good: Tough as nails, no brain required to operate, insane traction when on the gas, and OK for front and rear applications.
Bad: On-road handling quirks, susceptible to damage from a broken axleshaft, and can be a little rough on the street in the rear of short Jeeps.
Detroit Truetrac
Overview: The Truetrac is a geardriven limited slip that requires no special friction modifiers to operate. That means the bozo at the Qwikee Lube can't destroy your spendy limited slip by putting the wrong oil in. Under power, torque is sent to both tires unless there's an excessive amount of resistance on one.
Street:*****
The Truetrac is very unobtrusive on the street. When gassed in a corner or turn, you may feel the slightest pull, but there's no jerking or violent engagement of any sort. When under heavy throttle in a turn, the inside tire will bark a little, but not under normal driving conditions. Turning radius and tight maneuvers are totally unaffected.
Off-road:***1/2
The Truetrac offers near locker-like traction in all but the gnarliest terrain. We've found that modulating the brakes a bit can help keep one tire from spinning when the suspension is crossed up. You can't drive as elegantly in the rocks as you can with a spool or locker, but you'll have to work pretty hard to get stuck. In loose dirt twisties where you're lifting a tire, a Truetrac will almost always get you through.
Good: Great traction on- and off-road and can use straight 90W gear oil. They're moderately priced and great for front and rear applications.
Bad: There are a lot of little parts inside, so it's not as strong as most full-case lockers. Also, it doesn't offer as much traction as a locker or spool, and you may notice it (slightly) operating during some street driving.