Non-metallic piston in a heavy vehicle transmission and method of assembling the piston

A heavy vehicle transmission includes a multi-speed main gear box and an auxiliary gear box, such as a range or splitter gear box, coupled to the main gear box. The transmission assembly includes a shaft having an outwardly extending abutment element and a step portion. A piston constructed of non-metallic materials is mounted on the shaft. After the piston is mounted on the shaft, a retaining device is secured on the shaft for firmly retaining the piston on the shaft against the abutment element so the piston does not lean or tilt relative to the shaft to become misaligned or improperly seated, and the transmission assembly functions optimally. To accomplish this, the retaining device includes a spacing element and a locking member. The locking member is fastened on the shaft until the spacing element automatically abuts the step portion thereby retaining the piston of the assembly against the abutment element of the shaft. The step portion has a predetermined geometry on the shaft to facilitate quick and efficient assembly of the piston and the retaining device. A method for assembling the piston is also disclosed.