Jeep Liberty/Lockers/ARB Air Locker
The ARB Air Locker is an air operated manually controlled locker. The selectability of the ARB allows you to turn it on for traction off-road and leave it off for a smooth ride on road. The locker is normally unlocked and requires a constant (85 PSI min / 105 PSI max) air supply to lock. ARB manufacturers numerous small compressors to fulfill this air supply requirement.
Front Dana 30a
While the ARB RD100 and RD101 Air Locker have been installed in the Dana 30a without issue by many, it is not recommended by some because of the differential's aluminum housing. The force resulting from the ARB can crack the D30a housing more easily than it can a steel one. However, it has also been pointed out that whenever the front diff housing has cracked it has usually been the result of a rapidly spinning wheel making contact with the ground. With an ARB air locker in the front diff there would be no wheel spin in the first place and therefore a lesser chance of cracking the diff housing. Putting a locker in the front differential will not affect on-road and most off-road steering as the ARB is selectable and should be set to "open" when not needed. You need the RD100 for 3.73 and up gears and the RD101 for 3.54 and down gears.
Rear Chrysler 8.25"
The ARB RD93 Air Locker is used most frequently in the rear of the Liberty because the rear differential is made of steel and won't crack as easily as the weaker aluminum front differential.