Took some time off today to just unwind and take a look at the tandem outside. Took the hub apart and found out why it wasn't working properly.
There wasn't a single locking nut or anti-rotation washer in place... well, there was one. But I don't think it can do its job anymore.
There were various small parts missing from the hub that should have been there. I guess that since it still brought me home these hubs are stronger than I thought.
I will be using new wheels I think, since these are old Dutch standard
26 x 1 3/8,
37-590mm wheels instead of the more common
559mm MTB 26 inch wheels.
Perhaps
27.5 inch/650B (ETRTO
584mm) will be a nice alternative. Can anyone say 42mm tyres on a tandem?
