Abstract: A pneumatic mechanism for incrementally adjusting a glass sheet washing machine of the type having upper and lower sets of brushes and rollers spaced apart vertically to wash sheets of glass of various thicknesses passing between the sets. The upper set of brushes and rollers is carried by an upper frame member and the lower set of brushes and rollers is carried by a lower frame member. The pneumatic mechanism includes a pair of stacked pneumatic cylinders arranged in lifting engagement with the upper frame member at each corner of the upper frame. A selector is provided to sequentially actuate one and then the other of the pneumatic cylinders in a stack to extend their piston rods which are of different lengths to raise the upper frame relative to the lower frame by incremental distances defined by the extended lengths of the respective piston rods.