The Transaxtion is a recent release of Duncan's, and it has a plastic transaxle. Here's Felix's mod to make it ball-bearing instead:

Hey, my name is Felix. Here's the transaxtion mod I came up with. In my personal opinion and from what other people tell me it kicks [uh, buttocks]!
First you need:
1. A Duncan transaxtion
2. any Proyo axle
3. 2 spacers (Yomegas work best)
4. A bearing (team losi works best)
5. Dremel tool (or something to cut the bolt)

Step 1
Take your dremel tool and cut of the head of the bolt so you have about 3/4 of an inch left. [I find that 1 inch is a little better, 3/4" was too short for me]

Step 2
Sand you spacers to about 0.088 of an inch (of till they are flush with the halves if you don't have a micrometer)

Now put the bearing and spacers on the axle and screw together then you have a great 1 hand yo-yo. Brake pads may be added, depends on you.

Thanks Felix, for this great mod! I have tried this myself and it plays extremely well. -Roger

Thanks to Eric Wolff for this mod!

What you see here is one sweet little fella'. The equal of a Pocket Rocket in play (though obviously not as nice looking), plays better than an Ace IMHO (though obviously not as nice looking):

1.) Take a Duncan Keychain Trans-Axtion and remove its guts (eeewwww!!!);
2.) Take 2 Yomega bearing spacers and grind them down from their original .110" thick to .0725" thick;
3.) Take a 1" long brass (or steel if you prefer) #6 screw/bolt and cut off the head leaving 3/4" and add a small bit of tape in the middle right where the bearing will go (the tape should be just enough so that the bearing fits snuggly on your new axle);
4.) Add a Yomega or Spintastics bearing (4mm or 5/32"x5/16");
5.) Screw everything together, add a Slick-6 string (it doesn't like thicker string for some reason), and GO!!!

Have fun,
Eric