By the mid of 1950s, a number of competing tractors offered actual
multi-speed transmissions. The Bradely walkbehind, opted for a variable
pitch pulley arrangement that mounted on an arm midway between the
engine and the clutch pulley. Separate belts ran from the variable
pulley forward to the engine and from the variable pulley back to the
clutch. A handle bar mounted lever placed slightly pressure on the arm
holding the variable pulley. Pushing forward forced one belt up in the
pulley while the other went down. Backward pressure caused the opposite
effect. The result of the moving belts in or out was a change in ratio.
It came standard with a reverse capability and a feature called a 'speed
changer'. Speed changers gave the tractor infinitely variable ground
speed capability without changing engine RPM. A speed changer is an element by means of which the speed governing system can be adjusted to change the speed of the generator set under conditions of single unit, isolated load operation, or to change the power output under conditions of parallel operation with an independent power source.
A dual speed changer allows operators access to increased power. Hitting the dual power button will mean the selected speed is reduced by a specified percentage. Motor actuated speed changer provides a means for remote speed control on hydraulic governors. They provide a controlled rate for speed or load changes.