A MAINTENANCE EE WAS TAKING A DRIVELINE OUT OF A 789 CAT HAUL TRUCK. THE EE STEPPED FROM THE CENTER CROSS FRAME MEMBER TO ONE OF THE BRAKE CANS WITH HIS RIGHT FOOT. THE EE THEN STEPPED ONTO TH E TRANSMISSION HAVING WITH HIS LEFT FOOT. THE EELEFT FOOT SLIPPED FROM THE TRANSMISSION HOUSING TWISTING THE LEFT KNEE.