A multiple-ratio automatic transmission comprising a first multiple-ratio gear unit (10) and a second simple planetary gear unit (12) arranged in series in a torque flow path, each gear unit having a reaction brake (38,48) that can be selectively activated and deactivated to effect a ratio change as the first gear unit is upshifted and the second gear unit is downshifted, ratio changes in each gear unit being effected by pressure-operated clutches and brakes, the brakes (30,48) having opposed pressure-apply and pressure-release chambers. Separate exhaust flow paths (ISR,OSR) are provided for a reaction brake release chamber and for a companion pressure-operated clutch. A pressure modifier valve circuit is provided for increasing the rate of response to a command for applying and releasing the clutch.