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The 1-2 shift characteristics of a 4-speed automatic transmission are examined. Shift quality fundamentals and ratio change mechanics are discussed, and shift quality metrics are introduced. A simple model is developed to describe the shift characteristics. Powertrain dynamometer data illustrate the effects of throttle position, band-brake capacity, spark timing, and transmission fluid temperature. Band-brake apply pressure largely determines the inertia phase output shaft torque. Retarded spark timing permits substantial reduction of vibration dose value at constant shift duration. Due to increased viscous torque from the drum interface oil film, band capacity significantly increases during the first 0.1-0.2 s of the inertia phase for temperatures less than 40 C.