I seem to remember posting an item on this subject but don't remember
seeing it, so here goes again in case it didn't get through.
The NSWGR 40 class were based not on the RSD series, but the RSC series,
which were A1A-A1A wheel arrangement.
> One advantage of the A1A-A1A over the Bo-Bo is the lower axle loading as
> there is six axles instead of four. I don't know if that is the reason it
> was used but it caused problems later with wheelslip caused by the
driving
> wheels wearing faster than the non-driving wheels. This then allowed one
> driving axle to lift the wheels off the rails as the centre wheels were
> larger which created a see-saw effect pivoting on the centre axle. That
is
> the reason the centre axle was removed from the units that went to Robe
> River, as the higher axle loading on four axles was no problem.
> Regards,
I cannot agree with Chris about uneven wear on the driven wheels causing
the "seesaw" effect. The bogies had equalising beams which ensured that all
wheels carried the same proportion of weight reagrdless of track
irregularity. The most likely reason the Robe River 40 class had the centre
axles removed would have been to increase the axle load of the driving
wheels. Considering the much larger loads which the locos would have
required to shunt, the extra weight on drivers would have been necessary
for efficient operation.
John McCallum.