hi Nico,
oh the heck...now i have onemore time to search for the words......so be patient and full of phantasy...
The coaches have "sliding gears", what would not be of any interest, because most other cars have, too.
But with the coaches, the drilling for the axles is not directly in the axle-gearbox. there is a sort of sleeve or bushing between.
For this sleeve,the drilling in the axlebox is MUCH too big.
Wouldnt be a problem though.....but the axles themselves are a bit to short to give all a proper direction. the ends of the axles are not deep enough in the sleeves.
The sleeves tend to "cant" or "tilt" and the axle gets some kind of clamp.
That effect is tricky:
when u lift the car and turn it over, the axles run smooth and fine.
Even when u lift it just to turn the axles, they run fine.
But everytime the weight of the coach (what is not too less.....) comes on the toggling sleeves, the moving gets clamped. Not completely, just a bit like braking.
e.g. my coaches dont move themselves on a 3% incline!!!!! The hard it is for the locos to pull them up!
I changed the axle-ends of one coach from 4mm to 3mm and put mini-ballbearings on. The axle-boxes are THAT instable, that sometimes i loose an axle of this car.....
the axles themselves werent longer because of the ballbearing!
But running is that fine then! Used to have no movement at all, i just put the car on a place where i thought it should be even. It took a long starting along a 4% incline and made the following 1200mm radius-curve on the outer wheels, ran through an even, 6m long station and bumped into the trackend.
All critical trackpoints with an about 1m freefall on concrete in case of derailment.
Nothing happened...all is fine.
I decided to go in, take a coffee and become a nervous breackdown.
Frank
P.S.: my solution with the ballbearings isnt very good....but at least, it IS one!