A brake booster and a method of assembling an output member thereof within a bore of a valve body. In this brake booster, a reaction disc engages a holder of a reaction transmitting assembly which is connected to a plunger of an input member. A guide is attached to a cylindrical head on a shaft of an output member by hooks on the end of a first plurality of legs that extend in a first direction from a cylindrical base. A second plurality of axial legs that extend from the cylindrical base in a second direction are connected to a support ring. The cylindrical base is located in the bore by the support ring being positioned on a shoulder in the valve body by a return spring such that a series of arcuate tabs on the cylindrical base urge a reaction disc retained by the cylindrical head into engagement with the holder.