Clutch, transmission, propeller shaft and differential
Clutch, transmission, propeller shaft and differential
This domain examines power flow from flywheel to wheels, clutch operation, manual gearbox overhaul, driveline angles and final drive.
Core rules
- Clutch pedal free play is typically 10–20 mm; the release bearing must not carry load when the pedal is released. Check for oil contamination before replacing.
- Manual gearbox: check endplay, synchro ring clearance and bearing preload. Shift forks must be centred; detents give the click.
- Propeller shaft: yokes at each end must be in phase, aligned, for a two-joint shaft. Measure runout and check centre bearing preload.
- Differential: backlash is measured at the ring gear with a dial gauge, typically 0.10–0.20 mm; pinion preload is set with a collapsible spacer. Tooth contact pattern shows where the load sits.
- Final drive ratio = ring gear teeth / pinion teeth.
Worked example
Engine 2,000 rpm, 4th gear 1.00:1, final drive 4.10:1, tyre rolling circumference 2.0 m. Wheel rpm = 2000/(1.00×4.10) = 488 rpm. Road speed = 488 × 2.0 m/min = 976 m/min = 58.6 km/h. In 5th gear 0.80:1, speed rises to 73 km/h at the same engine speed. This explains why a lower final drive improves acceleration but raises cruise rpm.
Traps
- Fitting a propeller shaft with yokes 90° out of phase, causing vibration.
- Measuring differential backlash with the pinion loose.
- Adjusting the clutch cable so there is no free play, loading the release bearing.
- Mixing gear oils with different friction modifiers in a limited-slip differential.