Transmission, Drivetrain, and Differential
Domain 3 follows torque from the engine to the road: clutch, gearbox, propeller shaft, final drive and differential.
Clutch and gearbox
A single-plate dry clutch transmits drive through friction lining, pressure plate and release bearing; pedal free play prevents slip and bearing wear. Sliding-mesh, constant-mesh and synchromesh boxes differ in how gears engage - synchromesh cones equalise shaft speeds before the dog clutch locks. Gear ratio = driven teeth ÷ driving teeth; overall ratio = gearbox ratio × final drive ratio. A torque converter does the clutch job with fluid in automatics.
Driveline and differential
The propeller shaft uses universal joints for angle changes and a slip joint for length change. The final drive reduces speed and turns the drive through 90°. The differential lets wheels run at different speeds in a turn - outer wheel faster, inner slower - while both are driven. If one wheel is held, the free wheel turns at twice crown-wheel speed.
Worked example
Engine 3000 rpm, third gear 1.5 : 1, final drive 4.0 : 1, rolling circumference 2 m. Overall ratio = 1.5 × 4.0 = 6.0. Wheel speed = 3000 ÷ 6 = 500 rpm. Road speed = 500 × 2 m = 1000 m/min = 60 km/h. The same road speed in a taller top gear needs fewer engine revolutions, which is why overdrive improves economy.
Traps that cost marks
Inverting the gear ratio; mixing km/h with m/s; claiming both wheels must turn at crown-wheel speed; ignoring clutch slip when revs rise without road speed; forgetting to check differential oil level and propeller-shaft joint play.