Abstract: A tamper-resistant technique for retaining the cover of an electronically controlled air pressure piston operated automatic overdrive shifter employed on the auxiliary section of a change-speed transmission for heavy on-highway truck. In one embodiment a spring loaded slider tracks movement of the piston to cam a locking pin into engagement with a blind bolt to prevent removal of the cover when the piston is not in the overdrive position thereby requiring test equipment to operate the controller for cover removal. In another embodiment, the cover mounting has portions frangibly removable upon installation with press-in discs covering the bolts thereafter to deter removal. In another embodiment, a blind recessed roll pin is driven through slots in the bolt head to deter removal.

Abstract: An auxiliary transmission section (14) shift control system (230)/method is provided which includes a control member (234) to prevent auxiliary section synchronized clutch (92, 128) damage if the main transmission section (12) is engaged during an auxiliary section shift. Upon sensing main section engagement during a shift into the auxiliary section high-speed ratio, the force used to engage the high speed ratio is reduced from a first to a considerably lower second level by reducing the pressurization of the actuating pressurized fluid. To accomplish this, a dual pressure pressure regulator assembly (234) is utilized.