I purchased a front differential axle assembly from a 2004 2.4L Sport KJ with factory 4.10 gear ratio from a local salvage yard for $395.00. I also purchased a rear axle assembly from a 2005 2.4L Sport KJ with factory 4.10 gear ratio through LKQ Online for $350.00 shipped to a commercial address. I removed the cover and inspected it before installing, with only 62K it was in really good shape I cleaned scuffed and repainted the cover then reinstalled it with new RTV I removed my front axle assembly while I already had my front suspension out during lifting. Instead of cutting the two front mounting bolts I decided to remove the mounting brackets from the differential instead and was able to drop the brackets out of the way after loosening the front two bolts that back up to the LCA mounting bolts and removing the others. After removing the front driveshaft I was able to slide the differential to the drive side slightly and slip it out of the passenger side mounting bracket and straight down to the ground then I was able to install the new front differential containing the factory set 4.10 gears. Once reinstalling all the mounting brackets and torqueing most parts to spec when I could find specs the front axle was in and ready to go. If you plan on replacing the front axle assembly without modifying the suspension please notice that the clevis must be removed in order to remove the CV axle which is necessary to remove the differential housing. Passenger side mounting bracket Drivers side mounting bracket removed Bolts that you can cut and remove and replace or just loosen and let them drop the mounting brackets. Mounting brackets hanging. CRUSTY! The rear was simple also the only major attachments are obviously the lower control arms, the shocks, the Y-Link attachment at the top of the housing, and the rear driveshaft. Before removing those attachment points, in my case my salvaged rear axle was very crusty and all the brake lines had been cut during its removal so I decided to use my factory caliper mounting brackets and brake lines from my 3.73 assembly. In order to do that I had to pop the cover and drain the fluid from both assemblies, remove the 8mm bolt holding the center pin inside the spider gears, then remove the center pin, slide the axle shafts slightly in toward the center, remove the C clips inside the spider gears, then replaced the center pin to prevent the spider gears from moving around, then pulled both axle shafts in order to have access to the studs holding the caliper mounting bracket to the axle housing. Let me tell you those studs were so corroded that after using an impact to remove the nuts the studs themselves were worthless. The dealership wanted $12 each for 8 new studs so I did some research and decided to replace the studs with grade 8 bolts and say screw it because there is no rotation on that piece they only used studs to make it easier for assembly at the factory. So after removing both sets of caliper brackets and putting the better set on my 4.10 assembly then I also had to remove the brake lines from the 3.73 assembly while it remained in the KJ. Luckily there were only a few 10mm bolts holding the line brackets and the caliper itself was free after removing it from the mounting plate, there is one vent bold that holds a block onto the top of the axle on the drivers side and had a vent tube for the axle housing that goes up above the gas tank. Its hexed for a 14mm wrench and wasn't bad to remove. Brake line block vent bolt Axle housings after removing the caliper brackets and studs After preparing the brakes for the salvage axle I removed all the mounting points including the lower control arms, shocks, the Y-Link connection and the rear driveshaft. The coil springs were able to be removed during this process too, but the coil springs and shocks make flexibility much more difficult when having to apply torque to rusty bolts so I tried to leave them in as long as I could. Once free, I rolled the axle assembly on to the cover plate side on top of a floor jack so that it I could drag it out. Then time to slide in the replacement housing with 4.10's. During my process I was lifting as well so before installing the salvage assembly I cleaned it and repainted it because it was in rough condition and also installed my new JBA extended bump stops and the JBA Y-link extension before sliding it in. Again I rolled the assembly onto the cover on top of the jack and rolled the jack back under the KJ to begin reinstallation. Keep in mind I would say the rear assembly probably weighs 150-200lbs and the front probably weighed 75-100lbs. After reconnection all the brake lines and mounting points and suspension it was ready to go back on the ground. The JBA Y-Link was tricky and I'm really not sure it served an pinion angle improvements, but it did remove stress from the Y-Link ball joint by reducing its angle after lifting. Grade 8's instead of studs for the brake caliper mounting bracket I had to only use one washer on the bottom bolt of the Y-link so that the bolt head didn't hit the sway bar I decided to give the red cover plate even more attitude with a KJ decal I found online. After the install I drove it around the block with no issues what so ever, torque and power to the ground response was much more noticeable so it was well worth the pain and price. Now when dropping into drive and letting off the brake, the jeep instantly starts rolling and would probably reach 5-10mph on its own, of course that's with only 245/65/17's. I'm anxious to see how it does for my new 265/75/16 (32"x10.50"x16") Nitto Trail Grapplers that weigh 62lbs each plus my powder coated MOAB's.