Brake booster comprising a valve plunger stop made of metal wire

A brake booster, comprising a booster piston provided wit a tubular hub enclosing distribution valve means actuated by a valve plunger which is movable axially in said hub and coupled to an input rod of the booster, and a stop key for the plunger which is made from metal wire and mounted elastically on said hub with at least one stop portion of said key housed in a radial cavity of said hub so as to cooperate in engagement with said valve plunger, characterized in that the hub comprises two opposite radial cavities and said key comprises stop portions facing one another which are joined by an intermediate arch, each radial cavity comprising a central portion for housing the respective stop portion of said key and an access portion opening outwardly, a transverse distance between connecting zones located between said central portions and said access portions of said two radial cavities being greater than spacing between said stop portions facing one another of said key, each stop portion extended by an end portion which comes to bear against a bearing surface of the respective central portion, each stop portion of said key comprising a strand portion which is essentially straight and extended at each end by a bend, and the respective central portion having a height which is slightly greater than an overall distance between outer edges of said bends.