Driveline
This domain tests propshafts, universal joints, constant-velocity joints, final drives, differentials, four-wheel-drive transfer cases and wheel bearings. The exam looks for understanding of how drive reaches the wheels and how speed differences are allowed during turns.
Core rules
A propshaft needs a slip joint for suspension movement and phased universal joints to avoid vibration. CV joints allow drive through large steering and suspension angles; a torn boot admits grit and water and quickly destroys the joint. The final drive provides a fixed gear reduction. An open differential divides torque equally but allows different wheel speeds; a locked or limited-slip differential limits speed difference. Transfer cases provide high and low ranges and may drive front and rear axles. Wheel-bearing preload and lubrication are critical.
Worked example
A rear-wheel-drive car turns with a 10 m radius to the vehicle centreline. Track is 1.50 m, so the inner wheel follows 9.25 m and the outer 10.75 m. If the inner wheel rotates at 30 km/h, the outer wheel speed is 30 x (10.75 / 9.25) = 34.9 km/h. The differential allows this 4.9 km/h difference; a locked differential would force tyre scrub.
Traps
Assuming an open differential sends equal speed to both wheels; it sends equal torque. Diagnosing a vibration without checking propshaft phasing and joint angles. Packing a CV joint with ordinary grease instead of the specified molybdenum-disulphide grease. Reusing a wheel bearing that has been removed with a press.