Rear hub problem/howto?

First guess is that you didn't screw on the cones far enough, so you
have way too much play in the bearings... or it could be worse than
that.

Check this site:
http://www.parktool.com/repair_help/howfix_hub.shtml

Good luck,

-Ron

Quoted message said:

Some time ago I opened the rear hub on my Nishiki 601 (it's
Shimano STX/STX RC, Parallax from '98). I disassembled some parts
and I think I took out some of the balls from the bearings though
I put them back almost immediately.

Not many miles after that some problems started: at first the
wheel did not rotate that fluidly, then later it started wobbling
a bit sideways (well if you grab the rim you can tilt it by maybe
1 cm).

That is a lot! There may be some major problem there.

Quoted message said:

Is there a good howto online how to service your rear hub and fix
problems like these? Previously somebody advised me to check the
preload on the wheel (quick lock) but I have little clue what it
should be set at.

A trace of play should be detectable when the quick release is partially
open, and should dissappear when fully closed. That's a way of testing
it's just right.

SB has some good tips on final adjustment (involving using two cone
spanners or two locknut spanners at the same time: a trick Park miss):
http://www.sheldonbrown.com/cone-adjustment.html

~PB

Quoted message said:

Some time ago I opened the rear hub on my Nishiki 601 (it's
Shimano STX/STX RC, Parallax from '98). I disassembled some parts
and I think I took out some of the balls from the bearings though
I put them back almost immediately.

Not many miles after that some problems started: at first the
wheel did not rotate that fluidly, then later it started wobbling
a bit sideways (well if you grab the rim you can tilt it by maybe
1 cm).

Is there a good howto online how to service your rear hub and fix
problems like these? Previously somebody advised me to check the
preload on the wheel (quick lock) but I have little clue what it
should be set at.

Count your balls.