Device for transmitting a temperature signal by mechanical means, which consists in the use of a thermostatic element (1) made from expandable material which, when the inner bearing heats up, pushes against a rod (2) secured to a disc-carrying piece (3) and, simultaneously, to a disc (4), which, if the temperature is sufficiently high, is displaced until it comes into contact with the outer cover (5) of the bearing mounted on the other side of the wheel, that is to say on the outside, and the higher the temperature reached by the inner bearing, the greater will be the pressure exerted by the disc (4) on the cover (5) and the more rapidly the threshold detection temperature will rise, which temperature will be picked up by the pick-up device located on the track. (FIG. 1)