John Deere 9000 combines are the result of a simultaneous engineering effort. New features, increased productivity, higher reliability, better serviceability, and safety result from customer surveys. A larger diameter cylinder/concave and new slope tolerant cleaning system increase capacity. Cab and controls offer improved visibility, comfort, handling and safety. Electronic governors improve engine performance. Power distribution gearcaes replace belt drives to improve reliability. A hydrostatic pump and motor control ground speed. The hydraulic system is controlled with hydro-electronic valves. A header disengage switch is located in the operator's seat.