Gov-Loc
Overview: Manufactured for General Motors by Eaton, the Gov-Loc is really a marvel of engineering. It functions as an open diff when unlocked. When the difference in wheelspeed from one side to the other reaches a certain point, centrifugal weights expand and cause the differential to go from an open to locked diff in milliseconds.
Street:
It's fine when it's functioning as an open diff, but wheelspin is actually required to get a Gov-Loc to engage. Usually, once there is enough wheelspin present, the vehicle bangs and jerks when the locker engages. It just feels violent-and we're sure it is.
Off-road:
Like the street, the Gov-Loc requires a fair bit of wheelspeed before it will engage. You really feel like you're about to blast off, then BANG, away you go. The violence with which a Gov-Loc engages is one reason we see so many of them being replaced at our local 4x4 shop. Once you add larger tires or hit some hard off-road trails, the Gov-Loc usually blows its fine, Swiss-watch-like internals to dust.
Good: Available in many factory GM 10-, 12-, and 14-bolt rear axles.
Bad: They're not durable and you'll almost certainly be replacing it with one of the other aftermarket differentials listed in this story.
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:
Is a replacement for spider gears that fits inside stock differential carrier. Geared teeth and springs unload when coasting and lock under power.
Street:
Acts 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 is weaker than full-case counterparts, wears quicker, strength limited to stock carrier.
Notes:
Richmond Gear 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.