Here's a pic of Grinder No 1 in service 42 odd years ago.
http://tdu.to/Grinder1_SwanstonSt_11-2-1967.jpg

The truck nearest the driver moved the tram, while the other truck (as
mentioned by Kevin) was the actual grinding mechanism and was powered
via the manila ropes visible between the two sections.

There is only one motor - it's visible behind the racks holding the
spare grinding wheels. It provides both the motive power to move the
grinder and/or runs the grinding wheels via mechanical linkages
including rope, belt and chain drives.

In the pic, you can see the driver apparently looking out the side of
the tram. He is in fact face on to the controller which is placed
against the side of the cab.

The grinding truck is able to be split (down the longitudinal axis) to
enable the ropes to be removed without being cut and re-spliced.

When the vehicle was being transported from Preston to Bylands, Doug
Prosser tells me that he intervened at the last moment to stop the ropes
being cut and showed the crew how to split the truck.

There's an earlier post (with a pic from the other side on the same day) at:
http://tdu.to/3902.msg
You can see the belt drive that Kevin referred to.

What an amazing piece of equipment!

Mal Rowe, in the city where Grinder 1 was designed and built