gearbox vs gearing

gearbox

noun
  • That part of a car's transmission containing the train of gears, and to which the gear lever is connected. 

  • An enclosed gear train. 

gearing

noun
  • The ratio of a system of gears. 

  • Harness; working implements. 

  • Synonym of leverage (“debt-to-equity ratio”) 

  • A train of toothed wheels and pinions. 

How often have the words gearbox and gearing occurred in a corpus of books? (source: Google Ngram Viewer )