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Detroit Locker vs Selectable Locker for the Jeep Grand Cherokee ZJ with Ford 8.8 Axle

What’s the best rear differential for a Jeep?

I have a 1994 Grand Cherokee, 5.2 V-8, automatic, NP242, Dana 30 front and a Ford 8.8 rear with the factory limited-slip differential, both with 4:10 gears and 33-inch tires. This is my daily driver, but it also sees medium trail use on the weekends. I am considering a locker for the rear axle. Obviously, some kind of selectable locker would be my best option, but the purchase price is a bit out of my reach. Would a Detroit Locker work well on the street? I have heard horror stories about these lockers in short-wheelbase and lightweight rigs, but my rig doesn't fit into either of those categories. If not a Detroit Locker, what would you recommend for a budget-friendly option for a rear locker that will also work on the road?

Ed G.
Via email

You are correct in saying that a selectable locker is a really good option for your daily driver. Lockers are awesome off the pavement, but they do introduce handling quirks on the street. Some of us here have always been fans of automatic lockers like the Detroit Locker, mostly because we often forget to hit the button on a selectable locker before attempting an obstacle. But there's no denying that a selectable locker is probably the best choice for a daily driver. Selectable lockers provide all the good manners of an open differential on the street, plus the ultimate traction of a locker off-road. If your rig spends a healthy amount of time on and off the pavement, then these attributes are hard to beat even if the price point is a little higher.

All automatic lockers have their quirks on the pavement regardless of the manufacturer. They can cause the vehicle to corner funny, introduce some additional drivetrain "slop," and can make funny ratcheting and popping noises from time to time. The severity of these quirks will vary according to the manufacturer, the axle type, and in our experience, even from locker to locker from the same manufacturer. We've experienced lockers that were practically silent and others that you'd swear were broken with all the popping and banging they made. You also bring up a good point that vehicle weight and wheelbase are factors. Generally speaking, the handling quirks of a locker are less noticeable on longer-wheelbase vehicles, and those that are heavier. A locker in a TJ will be much more noticeable than in a fullsize truck, and your Grand Cherokee would fall somewhere in between the two. Driving habits are another factor; altering your driving habits by doing things like coasting around a corner whenever possible will reduce how noticeable a locker is to you and your passengers. Slightly conflating these generalities, a vehicle with a solid, stiff suspension will slightly mitigate some of the quirks of an automatic locker, and a vehicle with a flexy, slinky suspension may exacerbate them. So, for example, a YJ may (not will, but may) be less affected than a TJ even though they have the same wheelbase. Or, in your case, a SJ fullsize Jeep with leaf springs may notice an auto locker a bit less than a quad-coiled slinky Grand Cherokee.

Before pulling the trigger on an automatic locker, however, you should ask yourself a few questions. First, are you the only one that drives your vehicle? You knowing and understanding what a locker does to a vehicle on the pavement is one thing, but what about other family members who might get behind the wheel? There's also climate. If you live where it gets pretty cold in the winter, know that a locker on an icy road is not a whole lot of fun. Last, there's your own tolerance level. What may be no big deal to some people might be completely unacceptable to others. If possible, spend some time behind the wheel of a vehicle equipped with the locker you're considering and draw your own conclusions. Based on these factors, it might be best to hold off a little longer and save up for a selectable locker, or go ahead with your plans for an automatic locker.

Our last thoughts are that there's some chance a locker isn't the best choice for your application. If you're spending 95 percent of your time on the street and only 5 percent of your time hitting relatively mild trails, there's a chance that a limited-slip would be a smart choice. The stock Ford limited-slips leave a lot to be desired, but an Auburn or Eaton Truetrac are both quality aftermarket options. Also note that lunchbox-style lockers are the least expensive option, but all of them require an open differential. Your limited-slip carrier is incompatible, and by the time you buy an open carrier and have the ring and pinion setup for the new carrier, you're at nearly the same price as a full locking differential or limited-slip.

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