Abstract: A mixing machine comprising a housing having an upper portion and a lower portion, an attachment drive head extending downwardly from the upper portion of the housing, an attachment drive including an attachment drive shaft, the shaft being capable of driving a detachable mixing attachment, an adjustable drive train linked to the attachment drive for driving the attachment drive shaft, a motor mounted in the housing for driving the drive train, a shift lever assembly including a shift lever wherein movement of the shift lever adjusts the length of the adjustable drive train and thereby changes the speed of the attachment drive, and a mechanism mounted on the housing to prevent the shift lever from vibrating out of position during a mixing operation and to prevent a change in speed of the mixing machine.