High performance engineering thermoplastics are replacing metal in automotive applications due to the many advantages they provide. Directly converting from metal parts to plastic parts requires more than a material change. It requires a more detailed approach to component design and test. This is primarily due to the differences in material properties and characteristics between the two classes of materials. This paper illustrates that PPS engineering thermoplastic automotive transmission parts can successfully be developed if the additional attention to detail and testing are included. This enables the advantages of plastic in these applications to be realized. The objective is to illustrate to other analysts what is required in the development of plastic parts when replacing metal. This is done by giving a historical account of the analysis and test cycles used during the development of three internally pressurized transmission components, highlighting the key design issues. Results from finite element analysis and laboratory testing are discussed.