Abstract: An apparatus for controlling the lateral disposition of a guide roller of a traveling service unit on a textile machine is provided. The apparatus includes a first support wheel rotatably mounted on the traveling service unit and an adjustable wheel assembly. The adjustable wheel assembly includes a second support wheel laterally spaced from the first support wheel, a device for rotatably mounting the second wheel to the traveling service unit and a device for selectively adjusting the vertical displacement of the second wheel relative to the traveling service unit to maintain the guide roller at a predetermined disposition relative to a guide surface of the textile machine. The device for selectively adjusting the vertical displacement of the second wheel includes, in one aspect of the invention, a cylinder and piston assembly and, in another aspect of the invention, a pair of bell cranks interconnected to one another by a cylinder and piston assembly.