What was found
(CAN) ON DEPARTURE FROM AUA - YYZ, A MODERATELY STEADY LATERAL AIRFRAME OSCILLATION ( AT APPROXIMATE RATE OF TWO PER SECOND) STARTED AT 180 KNOTS / 2100 FT ABOVE SEA LEVEL / FLAPS 4 DEGREES. IT STOPPED ONLY WHEN POWER WAS REDUCED TO 1.4 EPR AT 5100 FT ABOVE SEA LEVEL / 260 KNOTS / FLAPS 0 DEGREES. ALL FLIGHT CONTROLS (SURFACE POSITION INDICATOR), HYDRAULIC (QTY.+ PRESS.) AND ENGINE (RPM.TGT,VIB+OIL SYST.)INDICATIONS NORMAL. AUTOPILOT OFF. CABIN CREW REPORTED OSCILLATIONS WERE FELT THROUGHOUT THE CABIN.- NR 1 YAW RATE GYRO WAS REPLACED IN ACCORDANCE WITH M.M. 22-15-02.