Which of the following lock-up clutch components is usually located in the front half of the converter shell?

• A. Backing plate
• B. Friction disc
• C. Ground shaft
• D. Hydraulic piston

Answer: (D)

The action being tested is how the lock-up clutch is actuated inside a torque converter. The key point is that the hydraulic piston does the clamping action that engages the lock-up clutch. Placing this piston in the front half of the converter shell allows direct receipt of hydraulic pressure from the transmission’s oil pump and puts the piston right against the clutch pack that sits between the impeller (engine side) and the turbine (transmission input). When hydraulic fluid pushes the piston, it clamps the clutch plates together, locking the turbine to the impeller and eliminating slip at cruising speeds for better efficiency.

The backing plate is a structural part of the clutch assembly, the friction discs are the surfaces that actually transfer torque when pressed together, and the ground shaft isn’t part of the lock-up actuator located in the converter housing.