Transmission differential, in particular for a motor vehicle, comprising at least: - a casing that is able to be rotationally connected to an input ring gear, said casing being made in one piece and comprising at least one transverse opening for accessing an interior cavity delimited by the casing, - pinions (26, 28) comprising two output sun gears that are centred on a longitudinal axis of the differential and are connected by meshing to two planet gears that are rotationally mounted on a vertical shaft, the sun gears and the planet gears being respectively mounted inside the cavity by virtue at least of one of said transverse openings or of said transverse opening, and - friction means of the differential, comprising at least one friction washer that is interposed longitudinally between each sun gear and the casing and at least one friction washer that is interposed vertically between each planet gear and the casing, characterized in that each of the friction washers that is associated with a sun gear comprises indicator means for allowing, in the operating position, the presence thereof to be visually checked through at least one of said openings or said opening in the casing, said means for indicating the presence of a friction washer being formed by a given number N of between 3 and 9 protruding elements that extend radially outwards from an external circumferential edge of said friction washer, projecting beyond the meshing means of the associated pinion, and that are circumferentially distributed in a regular manner so as to ensure effective visual checking through the opening, independently of the angular position of said friction washer relative to the opening in the casing and relative to the pinion with which said washer is associated. - a casing that is able to be rotationally connected to an input ring gear, said casing being made in one piece and comprising at least one transverse opening for accessing an interior cavity delimited by the casing, - pinions (26, 28) comprising two output sun gears that are centred on a longitudinal axis of the differential and are connected by meshing to two planet gears that are rotationally mounted on a vertical shaft, the sun gears and the planet gears being respectively mounted inside the cavity by virtue at least of one of said transverse openings or of said transverse opening, and - friction means of the differential, comprising at least one friction washer that is interposed longitudinally between each sun gear and the casing and at least one friction washer that is interposed vertically between each planet gear and the casing, characterized in that each of the friction washers that is associated with a sun gear comprises indicator means for allowing, in the operating position, the presence thereof to be visually checked through at least one of said openings or said opening in the casing, said means for indicating the presence of a friction washer being formed by a given number N of between 3 and 9 protruding elements that extend radially outwards from an external circumferential edge of said friction washer, projecting beyond the meshing means of the associated pinion, and that are circumferentially distributed in a regular manner so as to ensure effective visual checking through the opening, independently of the angular position of said friction washer relative to the opening in the casing and relative to the pinion with which said washer is associated.