Fixing assembly for fixing a window regulator pulley to a base of thermoplastic material, the base having a connecting area and a support area, the fixing assembly comprising: - the pulley, the pulley having an orifice concentric with a rotation axis of the pulley; - the base; - a support (30a, 30c, 30d, 30e) comprising two parts: - a cylindrical shaft (31h, 31i) and - a connecting element (32h, 32i) which can be connected to the base in the connecting area, the cylindrical shaft (31h, 31i) having: - a first end (33h, 33i) by means of which it is joined to the connecting element (32h, 32i) so that the cylindrical shaft (31h, 31i) is connected to the base through the connecting element (32h, 32i), and - a second end (34h, 34i) opposite the first end (33h, 33i), the cylindrical shaft (31h, 31i) being secured by the first end (33h, 33i) and the second end (34h, 34i), so that the pulley is positioned between both ends; - a support piece (50h, 50i) comprising: - a fixing part (51h, 51i) with a fixing orifice (53h, 53i), and - a support part (52h, 52i); the cylindrical shaft (31h, 31i) being secured by its second end (34h, 34i) to the support piece (50h, 50i) through the fixing orifice (53h, 53i), the support piece (50h, 50i) being in turn supported by the base through the support part (52h, 52i) which is designed to rest on the support area, so that the cylindrical shaft (31h, 31i) is supported through its first end (33h, 33i) joined to the connecting element (32h, 32i) and its second end (34h, 34i) through the support piece (50h, 50i), and so that the pulley is retained between the base and the support piece (50h, 50i); wherein the cylindrical shaft (31h, 31i) is an extension of the base, and the connecting element (32h, 32i) forms an integral part of the base; wherein the fixing assembly further comprises a cylindrical element in the form of a bushing between the cylindrical shaft (31h, 31i) and the pulley; characterized in that the support area of the base comprises a wall or groove, designed to receive the support part (52h, 52i) and improve the transmission of forces between them both. - the pulley, the pulley having an orifice concentric with a rotation axis of the pulley; - the base; - a support (30a, 30c, 30d, 30e) comprising two parts: - a cylindrical shaft (31h, 31i) and - a connecting element (32h, 32i) which can be connected to the base in the connecting area, the cylindrical shaft (31h, 31i) having: - a first end (33h, 33i) by means of which it is joined to the connecting element (32h, 32i) so that the cylindrical shaft (31h, 31i) is connected to the base through the connecting element (32h, 32i), and - a second end (34h, 34i) opposite the first end (33h, 33i), the cylindrical shaft (31h, 31i) being secured by the first end (33h, 33i) and the second end (34h, 34i), so that the pulley is positioned between both ends; - a cylindrical shaft (31h, 31i) and - a connecting element (32h, 32i) which can be connected to the base in the connecting area, - a first end (33h, 33i) by means of which it is joined to the connecting element (32h, 32i) so that the cylindrical shaft (31h, 31i) is connected to the base through the connecting element (32h, 32i), and - a second end (34h, 34i) opposite the first end (33h, 33i), the cylindrical shaft (31h, 31i) being secured by the first end (33h, 33i) and the second end (34h, 34i), so that the pulley is positioned between both ends; - a support piece (50h, 50i) comprising: - a fixing part (51h, 51i) with a fixing orifice (53h, 53i), and - a support part (52h, 52i); - a fixing part (51h, 51i) with a fixing orifice (53h, 53i), and - a support part (52h, 52i);