Gearbox with internal diaphragm

A method of configuring a gearbox for an irrigation system for operation, the method comprising:

• providing a gearbox comprising:
• a housing including a housing body and a housing cover;
• an output shaft;
• a worm gear within the housing;
• a bull gear within the housing and configured to be engaged with the worm gear and drive the output shaft;
• a vent configured to maintain pressure within a first chamber at substantially atmospheric pressure;
• securing a diaphragm to the housing cover with a retention member, the diaphragm positioned within the housing defining the first chamber fluidically sealed from a second chamber, wherein the first chamber is disposed within the housing cover, wherein the bull gear and the worm gear are positioned within the second chamber, wherein the retention member defines a plurality of expansion zones of the diaphragm, wherein the retention member is configured to limit movement of the diaphragm;
• filling, through an input port, the entirety of the second chamber of the gearbox with a lubricant such that the lubricant displaces the air within the second chamber;
• and
• sealing the input port so that air is prevented from entering the second chamber during operation of the gearbox.