The conversion can be carried out very rapidly, without any specific effort, without tools, and without adding new components. At the rear of the vehicle two panels 1, 2 each comprising a glazed part, articulated at their respective ends 6, 7, 21, with seals, produce either, when lowered on the bodywork, the rear screen and the top of the boot of the saloon or, in the raised position, the roof of the tailgate part of the estate respectively. Two movable side windows 4, when mounted, form the upper sides of the estate. They are lowered into the lower part of the bodywork for the saloon position. A closing flap 3, articulated to the end of the panel 2, ensures closing on a third panel 5 which opens from front to rear. A removable cover is placed either on the panel 1 protecting from the sun, or the panel 2 preventing the inside of the boot from being seen.