Trac-Lok
Overview: The Trac-Lok is the OEM limited slip differential offered in many vehicles-from early CJs from the mid-'70s up through XJs and some TJs. It uses stacks of friction discs that hold the spider gears from differentiating until enough torque is generated by the shafts to let them spin.
Street:*****
You'll think you're driving an open diff. The Trac-Lok is largely unnoticeable.
Off-road:*
You'll think you're driving an open diff. The Trac-Lok is largely unnoticeable. Unless it's new from the factory, don't expect anything but poor performance off-road from a Trac-Lok.
Good: It probably came in your Jeep from the factory. The unit can be rebuilt at home.
Bad: They require gear oil with a friction modifier and have wearable clutches inside. If you're planning on adding a lunchbox locker, you'll need to order a special application that will work with the clutch disc recess in the case. The recess inside of the case makes it slightly weaker than a standard open diff case.
It's difficult to weld into a spool if that's your thing. Basically, they don't work well, so don't waste your money. You're better off with an open diff.
Welded Diff
Overview: In a normal open differential, a set of spider gears allows the axleshafts to spin at different rates for smooth turning. Welding these gears together and then to the differential case sides creates a poor-man's spool.
Street:*
Overall, the welded diff will behave just like a spool. In some instances where the axleshafts are of a smaller diameter (1.30-inch and smaller), there may be some torsional loading and unloading of the axleshafts when used with sticky tires. This will make for more tire squeal and chirping when turning. Basically, the welded diff loses a point to the spool because of the potential for the welds breaking, not due to any difference in performance.
Off-road:****
Again, it loses a point to the spool because of the potential for failure, but as long as your welds hold, you're good to go. Like a spool, we wouldn't recommend a welded diff for a front application. We pulled our welded Trac-Lok apart after about 30,000 road and trail miles and found that a crack was beginning to develop in a weld near the side of the case. Left alone, the weld could fail, sending chunks of diff into the gears and bearings. So if you decide to run a welded diff, plan on checking it frequently.
Good: Dirt cheap and gives great traction.
Bad: It's pretty butch, and the finished product will only be as good as your welds and the strength of the stock case. It's really only good for some rear-axle applications.
Lunchbox Lockers
There are tons of drop-in lockers designed to replace your factory differential gears. We've used several with generally poor results. While we consider lunchbox lockers a good beginner or temporary locker, we wouldn't count on one as a permanent modification. Many of the companies that make lunchbox lockers also make full-case lockers, so if you've got the money, step up to the plate. Their operation and installation are similar enough that we'll lump their performance into one general category, then give more detailed descriptions below.
Overview: Replacement for spider gears that fits inside stock differential carrier. Geared teeth and springs unload when coasting and lock under power.
Street:*
Act like normal automatic locker, so normal jerks and banging associated with automatic lockers apply.
Off-road:***
Locker-like traction when working properly, but gear teeth are susceptible to wear and failure. When worn, it may not lock or unlock smoothly. When the unit fails to lock, it will leave you with no drive in that axle. Very susceptible to damage from axleshaft failure, and strength of stock carrier can be a factor.
Good: Inexpensive, easy installation, no gear setup required. Can be used in front and rear applications.
Bad: Generally weaker than full-case counterparts, wear quicker, strength limited to stock carrier.
Notes: Powertrax Lock-Right: Easy installation. Doesn't work well with short wheelbases or manual trannies. With hard use, the teeth will wear and round off on edges for weird engagement/disengagement. Pins that hold locker halves together can shear under extreme shock load. Good factory warranty service.
Detroit E-Z: Very violent on-road handling in rear of lifted TJ. Crisp engagement of new unit.