Transmission, drivetrain and clutch systems
Transmission, drivetrain and clutch systems
This domain covers power transfer from engine to wheels: clutch operation, manual gearbox, driveshafts and CV joints, differential, and basic automatic transmission checks. The exam tests observation, measurement, and correct lubricant and assembly practice.
Core rules and concepts
- The clutch must engage smoothly and hold torque. Check pedal free play, cable or hydraulic release, master and slave cylinder leaks, and release bearing noise.
- A slipping clutch shows engine speed rising without road speed under load; a dragging clutch shows difficult engagement and grinding.
- Manual gearbox faults include whine in one gear, jumping out of gear, and hard shifting. Check oil level and specification, linkage, detents, and bearings.
- CV joints: clicking on turns indicates outer joint wear; vibration under acceleration can be an inner joint or driveshaft.
- Differential whine on drive versus coast helps locate pinion or ring gear faults; check backlash and oil.
- Automatic transmission: check fluid level at the specified temperature, condition, and scan tool codes; do not road-test a severely slipping unit.
Worked example
A manual car slips in third gear on a hill. Pedal free play is 5 mm, so the release bearing is not holding the clutch partly disengaged. Road test confirms engine rpm rises but road speed does not. Inspect the clutch: worn friction disc or oil contamination is likely. A dragging clutch would grind into first and creep, which is a different fault.
Traps that cost marks
Riding the clutch; using engine oil in a gearbox; reusing a release bearing; overfilling an automatic; and diagnosing a CV click as a wheel bearing.