Thrust Washer
A flat washer designed to act as a bearing surface and control lateral or axial movement of a rotating shaft.
A thrust washer is a flat, ring-shaped washer made of bronze, steel, or composite materials, designed to handle axial load (thrust) along a rotating shaft. While standard radial bearings handle perpendicular forces, a thrust washer controls back-and-forth (lateral) movement of a shaft, preventing it from sliding out of alignment under load.
In automotive engines, thrust washers (often integrated with the main crankshaft bearings) are positioned on the sides of a crankshaft journal to limit crankshaft endplay. When a driver presses the clutch in a manual car, it pushes the crankshaft forward; the thrust washers absorb this force, preventing the steel crankshaft from grinding against the engine block.
Thrust washers are also widely used inside differentials, steering gearboxes, and transmissions. If thrust washers wear down due to oil starvation or high mileage, endplay increases, leading to mechanical noise, shaft misalignment, and potential catastrophic damage to the engine block or gears.