Transmission, Clutch, Gearbox and Driveline
What the exam tests
This domain tests how engine torque reaches the wheels: clutch operation, manual gearbox layout, final drive and differential, propeller shafts, universal joints and drive shafts.
Core rules
- The clutch connects and disconnects engine and gearbox. Main parts: flywheel, friction disc, pressure plate, release bearing, release fork and cable or hydraulic release system.
- A manual gearbox uses input shaft, countershaft, mainshaft, synchromesh units and selector forks. Synchromesh matches shaft speeds before engagement.
- The driveline includes propeller shaft, universal joints, differential, final drive and axle shafts. The differential allows wheels to turn at different speeds in a corner.
- Gear oil must meet the specified grade; the wrong oil can damage synchromesh and bearings.
Worked example
A car accelerates but engine speed rises faster than road speed, especially uphill. Reasoning: this is clutch slip, not a gearbox ratio fault. Possible causes are a worn friction disc, weak pressure plate, oil contamination or incorrect release adjustment. A road test in a high gear confirms slip; the repair is clutch replacement after checking the release system and rear main seal for oil leaks.
Traps that cost marks
Confusing slip with dragging, riding the clutch, coasting in neutral, using engine oil in a gearbox, and ignoring universal-joint vibration. Also remember that a differential does not multiply torque like a gearbox; it provides final drive reduction and allows wheel-speed difference.