Original page created on 17/02/2023.
Observation
These Roco wagons, ref. 76178, have a bad running due to the wheels rubbing on the chassis underside.
Looking for the cause
I try to find the rubbing areas, with a wheel set on which I glued sandpaper strips. At first, I hoped I could get rid of the rubbing parts with that device, but it turned out to be impossible: I could hardly have the “abrasive” wheels rotate.
But this allowed me to see where it was jamming: at the bridges that connect the brake blocks.
Correction
For the previously purchased Eds hoppers, which had the same defect, I had milled these areas directly. This was tricky and able to damage the surrounding parts. So I decided to dismantle these bridges, which was sometimes difficult, and then machine them at the workbench.
To remove them, it seems more convenient to start with the outer pin, by attacking them from the top of the chassis. Here they are dismantled.
Below, you can see one bridge still intact, the other cut in three. The central part is deleted. Each remaining support is milled to round off the protruding part.
The supports are put back in place — not without some difficulty — and then glued with CA glue.
The clearance is such that it is even possible to fit wheels of the correct diameter (11.5 instead of 11.0).
Result: On the right, a modified wagon that has been fitted with detail parts (railings, chutes) and Piko ⌀ 11.5 wheels. On the left, an unmodified “bare” wagon. There is obviously a small difference in height.
The improvement due to the larger wheels is not obvious, but the most important thing, which is not visible, is that the modified wagon runs well now!