Automatic and Manual Transmissions and Transaxles
Core concepts
Understand torque converter operation (impeller, turbine, stator), planetary gear sets, clutches and bands, and how a valve body directs hydraulic pressure. For automatics, know line pressure, shift solenoids, and the role of the transmission control module (TCM). For manuals, know clutch operation, synchronizers, and gear ratios. Be able to explain the difference between a transaxle and a transmission and how a differential integrates with a transaxle.
Traps to expect
Questions often blur hydraulic and electronic faults. A slipping automatic may be low fluid, a worn clutch pack, or a faulty pressure solenoid; do not assume a rebuild is needed. Watch for confusion between a torque converter's stator and turbine, and between clutch slip and engine misfire. Another trap is gear ratio math: overall ratio equals transmission ratio times final drive ratio. Also know that a manual transmission's synchronizers match shaft speeds; grinding on downshift suggests worn synchronizers or a dragging clutch.
Worked example
A vehicle has third gear ratio 1.00 and a final drive of 3.55. Overall ratio is 1.00 × 3.55 = 3.55:1. If first gear is 3.00, overall first is 3.00 × 3.55 = 10.65:1, which explains higher torque multiplication at low speed.
Study strategy
Trace power flow through each gear, practice reading a hydraulic circuit diagram, and explain how a scan tool reads solenoid commands and adaptive shift data.