I have done this in 2 different phases.
Phase one was when I removed the transmission (on jack stands, with a friend). When car is on ground, remove the TMIC (intercooler), turbo heat shield, and 5 turbo-to-downpipe bolts. That's 15 minutes if you know what you're doing, or 30 if your don't.
Next raise the car. Remove lower exhaust sections, as needed. Remove heat shield. Remove drive shaft (6 bolts if I remember correctly). Remove trans mount off tail housing (this trans mount is soft and does almost nothing). Remove speed sensor from tail housing (1 Bolt). This all is again 20 minutes if you know what you are doing, or 30 minutes if you don't, or an hour if you have inadequate tools.
My phase two was when I had the trans out of the car, though you shouldn't remove your trans unless you are doing a rebuild (me).
Remove tail housing from main case. Hammer tap output tail shaft out of housing (gently). Center diff will be staring you in the face. Pull snap ring, pull out gear pins (4), pull out planet gears (4). This is 5 minutes or an hour depending on how effective you are. My buddy just used a chisel, carefully, to separate the two housings. There was plenty of flange surface intact afterwards, as he only penetrated a few millimeters, so no problem. I wouldn't have been alright with this if it could have done damage.
Swap bearings with solid bushings. Old bearings literally fall out of their gear in their assembly.
Install all bushings in all 4 gears at once. Press fit or heat them up for interference fit. We are aiming for a 0.0000" to 0.0005" interference fit. Both bronze and steel have a coefficient of expansion roughly 9 or 10 x 10^6 in/in *F.
So with a delta of 100*F between the gear and bushing, the two should slide together with little or no force. So put the bushings in the freezer, and hold a flame to the gear, or just use a flame since you could easily get the gear to 200*F or 300*F. Do whatever you want, just wear gloves and be safe. Or press fit if that's easier. It really doesn't matter. Give yourself 30 minutes to be sure you get this right. You don't want to have the bushing sticking out one side of the gear because you placed it in wrong. If you do that you will need to tap it to centered.
Put it all back together, with new trans case gasket, and new exhaust gaskets, where needed. Go drive. If everything is in good shape, try a few launches. Just beware, there is no guarantee you won't break anything when you launch, especially when you are dealing with tons more torque over stock. There are no guarantees; all you can do is stack the odds in your favor
How many bushings in a set? Why?
There are 4 planet gears in each center diff, and each has a set of needle bearings in it, so to do this mod you need 4 total bearings for your one center diff. That is why they're in sets of 4. One set per center diff. None of this is in the actual transmission. It's all in the tail housing. I will clarify the two OPs.
Here look at this http://opposedforces.com/parts/legac...llustration_1/
#10 is the planet gear, of which there are four in the #16 Center Diff Carrier.
#5, #11, #5, find those. They sit inside each planet gear.
#5s are the needle bearings, two per gear. These are very small and not very strong. They are fine for stock power, but cannot handle much more.
#11 is the spacer between each set of needle bearings. Subaru could have put more needle bearing contact area inside the gear, but instead they put a spacer to fill the nothingness. The spacer does nothing except keeps the needle bearings at the ends of each gear.
#2 is the oiling pin, which goes inside the needle bearings inside the planet gears. The needle bearings rotate on this pin. One pin per gear. It is very strong, relative to the planet gear's needle bearings, but is probably the next weakest link in the center diff.
These solid bronze bushings will replace #5, #11, #5 with one solid bushing per gear. You're removing the two needle bearing and one spacer per gear, and putting in one solid heavy duty bushing. This will add a huge amount of contact area to spread out the torque between the #2 pin and the #10 gear.
If you were building an all-out drag race monster 5eat, you would probably want to consider replacing each of the four #2 pins with something a little thicker and a little harder, as strong a material as you could possibly find. But I don't know of anyone who would need something that crazy. For us who have more power and torque than stock, and still want to launch our cars like we did when they were stock, these bushings should add a lot of strength to your expensive center diff.
Courtesy of Frank_ster
Replace needle bearings on left with solid bearing-grade bronze aluminum bushing on right
How much stronger will this make my center diff?
Best we can do is speculate. Frank_ster thought it could be twice as strong. I think it will make it a LOT more than twice as strong. Both of us have taken apart the center diff and held the stock needle bearings. The stock needle bearings contact a very small fraction of the possible surface area between the gear and oiling pin. This mod spreads out the torque across the entire planet gear and entire oiling pin, making this weak point in the center differential significantly more durable.
Why do this mod?
The forum consensus is to never launch your 5eat or risk breaking your center diff. But launching at a stop light or at the drag strip is incredible fun and is a significant way in which you can use your AWD advantage over your FWD and RWD counterparts. So do it if you want to enjoy launching your car without living in fear that you are one snap away from a major repair.
Do I need this mod?
Do you torque break or launch your car?
Will these wear out over time?
The answer is unknown, but it is doubtful that these will wear out.
How do you install this mod?
It's pretty straightforward. Get a copy of the factory service manual, and follow the instructions to remove the center differential (transfer clutch).
Then take a plyers and remove the black snap ring. Then the center differential planets can come apart, and you are in.
To put everything back together, you need a new metal gasket to place between the transmission case and differential housing.
05 models have the center diff in two layers of housings. You want the gasket for the rear-most housing, part # 31337AA200.
At some point the center diff housing switches from 2 parts to only 1 part, so you use a different gasket, part # 31496AA010. I will find out the model year switch.