310T Drive Trains Practice Test 2026 - Free Drive Trains Practice Questions and Study Guide

Torque converter operation happens in two stages. First is torque multiplication: the impeller pushes fluid that slips relative to the turbine, and because the stator redirects that flow, the turbine ends up delivering more torque than the engine is actually producing at the same speed. This stage provides high torque at low to moderate speeds.

The second stage is the coupling (lock-up) phase: once enough speed is reached, a clutch inside the converter locks the impeller to the turbine, creating a direct mechanical link. That eliminates most slip and greatly improves efficiency and throttle response.

So the two phases are torque multiplication and coupling (lock-up). The term coupling here is another way to describe the lock-up action.