My clutch makes an incredible irritating shrieking sound which is coming from the slave piston ball bearing. I already tried to lubricate the bearing but the sounds returns after hundred kilometers or so. It only makes the sounds when the clutch is engaged, so during idling and riding, disengaged with the lever pulled in the sound disappears. Best way of getting rid of this sound is to replace the piston, I guess. Or is there a way to replace the bearing in the old piston? Except for the sound the clutch is still working perfectly and is not leaking oil.

Take a look here for some information:

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As it is winter in Holland, I have started repairs on my slave piston.
I have a piston with 2 bearings inside, where the upper bearing has loose bearing balls , the one of the 906. I replaced the balls with new ones and put new grease in it. Everything seems to run smooth . I am now waiting for a new oil seal for the piston before i can re-install it.