Transmission: Clutch, Gearbox, Differential and Drive Line
Clutch
A single-plate dry clutch transmits torque through friction between flywheel, friction disc and pressure plate. The release bearing disengages it via the release fork. Symptoms: slipping (worn disc, oil contamination, weak spring), dragging (faulty hydraulics, warped disc) and judder (contaminated or misaligned parts). Free play must be correct; too little causes slip, too much causes incomplete release.
Gearbox
Manual gearboxes use constant-mesh gears with synchromesh cones to equalise speeds before engagement. Gear ratio = driven teeth / driving teeth. Overall ratio multiplies gearbox and final drive ratios. Traps: reversing the ratio, ignoring the final drive, and confusing input and output shaft speeds.
Differential and drive line
A differential allows wheels to rotate at different speeds while transmitting torque; the crown wheel and pinion provide the final drive reduction. Limited-slip units add clutch packs or viscous coupling. Universal joints and constant-velocity joints handle angle changes; a worn joint causes vibration. Propshaft imbalance shows as speed-related vibration.
Worked example: gearbox ratio 3:1, final drive 4:1, engine 3000 rpm. Overall ratio = 12:1; wheel speed = 3000 / 12 = 250 rpm. Rule of thumb: lower numerical ratio means higher top speed but less torque multiplication.