A truck (1) for a railroad rehabilitation machine comprises a railway truck (3) and a tank (2) resting on the railway truck (3) in a removable manner. The tank (2) comprises a holding structure (5) extending along a predetermined direction (X), at least one first conveyor (8) mounted within the holding structure (5) to transport incoherent material along the predetermined direction (X) internallyof the holding structure (5), and means (22) for laying the holding structure (5) on the truck (3) for railway transport. A process for making a truck for a railway rehabilitation machine comprises the steps of arranging a railway truck (3) having a support platform (4), arranging a tank (2) for trucks of railroad rehabilitation machines in accordance with the invention and laying the tank (2) onthe platform (4) of the railway truck (3) in a removable manner.