Case Study: Thrust and Back-Up Washers

Process: Conventional powder metallurgy
Secondary Processes: Sintered, quenched & tempered
Material: Propriety low-alloy steel
Density: 7.1 g/cm³
Tensile Strength: 1,300 MPa (190,000 psi)
Yield Strength: 1,010 MPa (147,000 psi)

Thust and Back-Up Washers
2015 Grand Prize: Thust and Back-Up Washers

End Use and Function

The components, thrust and back-up washers, play a critical role in the function of Allison’s new TC10 automatic transmission for Class 8 (18-wheel) tractors.


Made using a proprietary low-alloy steel, the three parts are warm compacted to achieve high green density, then vacuum sintered at high temperature, gas-pressure quenched, and tempered. They’re produced very close to net shape, with only precision machining of some surfaces performed to improve the micro-finish and dimensional accuracy. They achieve a typical density of 7.1 g/cm³, 1,300 MPa (190,000 psi) ultimate tensile strength, 1,010 MPa (147,000 psi) yield strength, and an elongation of 1.7%.


  • A first of its kind for the trucking industry, this 10-speed automatic transmission enables even inexperienced drivers to achieve 5% fuel savings over typical manual transmissions, thus contributing to a significant lowering of CO₂ emissions.
  • While these washers were an original PM design, they’re estimated to save 30% over the cost of comparable forged/machined components.