Hello again,
Yesterday I had a go at my Nexus 8 hub in hope that this time I will find
something obviously wrong which could then be fixed.
At first I was optimistic because I found that the nut which locks the
roller brake assembly was loose, so maybe that was it I thought. I also got
rid of the washer inserted by the bike shop which did the previous
unsuccessful repair attempt. After assembling everything back together it
looked even better because I could dry-shift through all gears and the
cassette joint unit would happily go back and forth even back from lower
gears.
However the following test ride showed that the problem was still there, and
it even changed a bit and got slightly worse. Now I get intermittent loss
of power in 5th gear, like clutch temporarily slips for half a second. I
still mostly can't shift to 4th and lower, and still when trying I
sometimes get a complete loss of power when I have to manually pull back
the cassette join unit back into alignment.
I think I checked all of the suggested stuff I could. Anti-rotation washers
are fine, lock nuts seem fine (I played with the one on the sprocket side
to see the effect - to tight and the whole hub gets difficult to turn, so I
left it only slightly fastened as it was), chain is tight and everything
else seems fine (cables, stops, etc).
As next step I will be contacting one shop which may be capable of dealing
with Nexus and if so probably putting the bike in car and taking it there.
It shouldn't be more than 45 minutes drive one way so it's not so bad. I
really hope they confirm they can deal with Nexus because the next
candidate shop is roughly twice as far.
Tvrtko