I have looked through E Harper Charlton's book "Electric Railway Car
Trucks" and can find no truck resembling our mystery truck. He says his
book is not complete, but I doubt that a truck like this would have been
omitted if made in the USA or Canada.

Salient points are that the main frame passes under the axle-boxes in a
straight line, and that there are coil springs either side of the axle
boxes.  Very few of the Charlton diagrams have either of these features,
and so far as I could see, none have both.

i AM PUZZLED BY THE CONSTRUCTION OF THE TRUCK, AND PERHAPS SOME ERUDITE
truck lover can explain (and perhaps someone can say how unwanted upper
case letters can be got rid of without deleting and rewriting the whole
text!

The main side frame must be in compression and the upper in tension, as
they form a triangle linked by the vertical 'piece' immediately outside
the outer coil spring.  This vertical piece appears to be cast as part
of the lower side frame.  The axle boxes slide in hornways bolted to (I
presume) a projection from the main frame.  They have a small half
ecliptic spring on top. Now, the rail pushes up, the wheel pushes up,
the axle pushes up so the axle box pushes up so the spring is being
straightened. This spring appears to be connected to the top of the coil
spring, so the top of the coil spring is pushing up.  The coils springs
are sitting in a socket on the main frame, which is being pushed down by
the weight of the car, transmitted though the semi-elliptical springs
mounted on top of the frame extensions. So the coil spring is in
tension?????

A coil spring in tension? this seems to be rather unusual to me, though
it may well be the case.

If we number the large coil springs from left to right on the near side
of the truck,, just this side of number 2 spring is a 'bar' which
appears to extend to the other side of the truck, and which supports a
small spring, probably just this side of the half way point.
There appears to be nothing to go above this small spring.  Query, which
is its function?  Plausibly there is a similar spring a bit further
across, and I think a portion of this may be visible clear of the
nearest wheel, just above Number 3 large coil spring. Could these be to
support a motor which would drive the wheel by numbers 1 and 2 springs?

I would suggest that this was a prototype truck for a long single truck
car, where the mechanical engineer was dissatisfied with the performance
of the trucks on some of his single truck fleet. Decided to try and
experiment, was dissatisfied, and decided the best thing to do was to
scrap the single truck cars as soon as possible and replace them by a
large fleet of bogie cars. Possibly replaced by the "N" class cars in
Sydney?

Regards

Dudley Horscroft