Our cart, made by Odin in France, has three wheels, no suspension and
no brakes, and it works very well.  It also has solid rubber tires.
You might think this makes for a rough ride, but actually does not.
The organ generally is pushed along streets and sidewalks, and we just
avoid (or go slowly) through rough spots.

The "brake" is a rectangle made of four pieces of wood which, when
placed under one of the wheels, keeps the cart stationary.  The
Hofbauer cart I have has four wheels with pneumatic tires, and a light
spring suspension.  The brake is a plunger that pushes against a tire.
The suspension allows the organ to sway slightly when cranking, but
this is not a problem.

Phil Jamison