FF,

To replace the bearings:

Use two 8 mm allen keys to remove one of the end-caps (you have to use one on each end, but of course only one comes off unless you're extraordinarily lucky). Then put the allen bolt back in about half way on the side you removed the end-cap from and use a soft mallet (or piece of 2x4) to gently tap the axle out the other side. It'll come out with one bearing attached. Then clamp the middle of the axle in a vise (gently -- it's aluminum) (or use a vise grips if you don't have a vise) and remove the remaining end-cap. The attached bearing should pull off; if not, let the axle suspend between a couple pieces of 2x4 (or a vise), resting on the bearing; put the allen bolt part way into that end of the axle and tap lightly. It will pop the axle through, leaving the bearing behind.

To finish disassembly, push the bare axle through the hub and through the hole in the bearing remaining in the hub. Again screw in the allen bolt half way and tap the end of the bolt. You'll push out the remaining bearing. (The reason for screwing in the allen bolt every time is that if you tap the end of the bare axle, the aluminum will bend and you have to buy a new one.)

To reassemble is simple. Be sure you've taken off cogs and lockrings (not absolutely necessary, but it makes it much easier). Insert the axle, slip the new bearings on each end of the axle, and lay the old bearings directly over them. Then screw in the allen bolts (with the included track washers). You'll have a sandwich with the hub in the middle, two bearings resting on each face of the hub, and two allen bolts holding it all together. At that point, very carefully tighten the allen bolts on each side. They should go in relatively smoothly, and they should go in perfectly straight. If one starts to tilt sideways, stop, disassemble everything as you did previously, and start over. Sometimes it takes a time or two to be aligned just right. When it goes right, the two allen bolts will simply pull the new bearings right into their seats, using the old bearings to distribute the load and help align things. Tighten firmly and remove the allen bolts and the old bearings. Spin on the end caps, tighten LIGHTLY (too much at all and you'll feel the bearings bind up), and you're done.

As a safety precaution in reassembly, I prefer to spin a metric hex nut onto each allen bolt before tightening down. Then you can loosen the allen-nut head while holding onto the hex nut. If you don't do this, you can sometimes have one allen bolt come out with the other one stuck. The only way to handle that problem is to start all over by disassembling and reassembling. Which sucks.

Don't try to do this with a ride starting in five minutes. It takes a little patience but not much else. I've done it plenty of times, but I've learned not to rush it. Sometimes it takes an extra try.