first of all, i must give credit to this man, who (i think) pioneered the concept; i'm simply applying it to the xmod diffs.
http://s3.invisionfree.com/rcdrift/i...showtopic=4388
second of all, i apologize for the crappy picture quality; i should've done this in the morning so the camera wouldn't have to deal with artificial lighting, which it hates.
with that said, the purpose of this tutorial is to provide gen 1 owners with a way to make a better diff for themselves. it's as smooth as the ball diff, is adjustable like the ball diff, and yet retains the power transfer capabilities of the gear diff. you can lock it or leave it open, it's all up to you. this tutorial can probably be applied to evo diffs as well, though it'll be harder to keep the diff together and probably not adjustable (unless you modded it with an MR-02 kingpin or a screw).
so let's get started.
1. gather materials. you'll need your screwdriver, a hobby knife, side cutters, tweezers if you need them (not shown), superglue (not shown), your gear differential, a spare axle (not shown), spare plastic, and a cutting board.
2. disassemble the diff.
3. take the hobby knife and cut out two pieces of plastic from your spare plastic. for your own safety, make them at least the size of the gears in the picture.
4. take your knife again, and start a hole in one piece of your plastic. pick a spot, take your knife blade, and start turning the handle. eventually you'll go through the plastic, it shouldn't take too long.
5. pick up your piece and continue drilling. the picture below explains why i want you to make the pieces bigger than you need: the hobby knife should not be any closer to your fingers than needed.
6. continue drilling until the hole is about the size that the axle can fit snugly through. once that happens, scrape the burrs off and you should find that the axle fits a bit more loosely -- that is what we want.
7. this step will take some fine motor control. take your side cutters and trim around the hole; make the sides of your homemade shim as thin as possible. again, i apologize for the poor picture, but hopefully you get the gist of it.
8. repeat steps 4-7 for the other piece of plastic.
9. this step will require a lot of fine motor control, so be careful, and if you have tweezers, take them out. if you have a toothpick on hand, that would be very useful as well.
apply a tiny tiny dab of superglue to the broader, d-cut side of the diff gear (use a toothpick if you have one). next, slowly place the shim on top of the gear, and adjust its position till its hole lines up with the hole in the gear. use tweezers, toothpick, screwdriver, whatever, to make sure the shim lines up. when you're sure, take something and press down on the shim; let go after a couple seconds, and let the superglue dry.
repeat for other gear; at the end you should have two diff gears with a shim firmly glued to the tops. it's hard to see, but there is a slight reflection on the tops of these gears, caused by the clear plastic shim.
10. add a small dab of RS gear grease (the same size as your dabs of superglue) to each gear and reassemble the diff. turn the diff screws lightly, and stop the moment you encounter resistance.
11. adjusting: if you tighten the screws down all the way, the diff should basically be locked (unless you used some thinner plastic than i did). loosen the diff a quarter turn at a time until you get the effect you like. you can loosen the diff in the car, just stick the screwdriver through the wheel spokes, aim at the diff and you can probably reach the diff screws.
enjoy!