replacing rear joint assembly...

Welcome to the forums. I've never changed a u-joint on the 420, but it should be about the same process as any Honda SRA 4-wheeler. You will probably have to either, remove the swingarm and replace the u-joint or remove the brakes and brake backing plate and remove the axle and unbolt the differential and pull the driveshaft back and change it. The first option would probably be the easiest.

2wdRancherRider said:

dropped the swing arm and removed the old joint... which side of the joint would be the easiest to put on first? the side from the block or the side from the shaft?

Click to expand...

I don't know if it would make much difference, but I would probably put it on the output shaft first.

I agree, just look the boot over good and make sure it doesn't have any rips or holes in it and if it hasn't, reuse it. I would say that since the driveshaft and other parts are in the condition that you described, that it would be a good idea to go ahead and replace the u-joint because it's probably in bad condition too. If you don't replace it now, while everything is apart, you will just have to replace it later.