A mobile radiography system includes a wheeled transport frame and a vertical column mounted on the transport frame. A telescoping arm is attached to the vertical column and to an x-ray tube head. The telescoping arm includes a first section, a second section movable within the first section, and a third section movable within the second section. The first section and the second section each include a drag assembly configured to provide a drag force on the linearly movable section therewithin. The drag assemblies each include a friction material pressed against the linearly movable section to provide a constant drag force on the linearly movable section while it moves. A permanent pressure source presses the friction material against the linearly movable section.