Jeep Liberty/Dana 30a
The 27 spline Dana 30a, also know by Chrysler as the 186FIA, has always been the only front axle available in the Jeep Liberty. It's an IFS axle with an aluminum housing as indicated by the 'FI' and 'A'/'a' respectively. Essentially, it's an aluminum version of the Dana 30 with a longer pinion shaft. Unfortunately, the light weight aluminum construction makes it weaker than the D30 and the longer pinion shaft means pinion related D30 parts won't fit it. The D30a requires a 1-1/8" socket to remove and install the pinion nut.
CRD Libertys have a different front cradle that lowers and leftward shifts the differential to provide more clearance for the diesel engine. The lowering results in better half-shaft constant velocity joint angles but too little clearance for a differential collar. The leftward shift requires different length half-shafts than those used in the gas Liberty. Due to the shorter left side half shaft CRD models cannot be lifted as high before the CV joints begin to bind.
Traction Aiding Devices
The axle housing's aluminum construction is weak and installing a locker in the front differential could cause it to crack. It is recommended that an LSD be installed in place of a locker. It should be noted that installing any traction aiding device in the front will make steering slightly stiffer and cause the steering wheel to spring back to center more quickly than usual.
The gear lube in the Dana 30a should be changed every 12,000 miles. Off-roading and towing subject the differential to increased torque, dirt, and water. If the Liberty isn't off-roaded, isn't used for towing, and follows the Schedule A maintenance plan, it may be possible to stretch this interval. The differential housing requires 2.6 pints (1.24 liters) of lube. Since the Dana 30a doesn't have a removable differential cover that could allow to clean it, 75W-140 synthetic lube should be used for either light duty applications or heavy duty off-roading.
Mopar is the only manufacturer of the longer pinion gears required by the Dana 30a. As a result, there are only three sources of 4.10 gears for the Liberty's front differential: wrecked I4 Libertys, online stores that sell discounted Mopar parts, and Jeep dealerships.