A hinge joint for use in the seats of motor vehicles to permit changes of inclination of the back rest has a first leaf secured to the body supporting portion of the seat, a second leaf secured to the back rest and a composite shaft having an eccentric cylindrical portion turnably mounted in the first leaf and two coaxial conical portions flanking the eccentric portion and turnably mounting the second leaf. At least one conical portion has a cylindrical core of a metallic material and elastic sleeve surrounding the core and having a conical external surface. A diaphragm spring reacts against the shaft and urges the second leaf axially of the shaft against the first leaf, and a spur gear of the first leaf mates with an internal gear of the second leaf.