Abstract: A folding backrest for a passenger seat assembly in a motor vehicle comprises a backrest frame having a first end and a second end. First and second hinges pivotally support the respective first and second ends of the backrest frame about an imaginary horizontal folding axis for movement between a use position and a folded position. A pivot beating is formed in an tab extending from the first end of the backrest frame. A self-locking plastic bushing is positioned in the pivot beating. The pivot bearing and bushing together form a keyway having a pair of diametrically opposing notches. A floor bracket made of mirror-image right and left half sections retain a hinge pin in a perpendicularly extending fashion by sandwiching therebetween a central flange of the hinge pin. The hinge pin includes a keyed tip which is aligned and registerable with the keyway when the backrest frame is in the folded position to permit axial sliding connection between the pivot bearing and the hinge pin during the assembly process.