Transmission, driveline, steering and suspension systems
Domain focus
This section covers transmission, driveline, steering and suspension: how torque is multiplied and delivered, how the vehicle is steered, and how ride and wheel location are controlled. The exam tests component function, power flow, alignment angles and simple ratio calculations.
Core rules
- A clutch connects and disconnects engine and gearbox; it must engage smoothly without slip or drag.
- Manual gearboxes provide discrete ratios; final drive and differential reduce speed, multiply torque and allow wheels to turn at different speeds in a corner.
- Propeller shafts use universal joints and a slip joint; CV joints are common on independent drive shafts.
- Steering geometry includes camber, caster, toe and steering axis inclination; incorrect toe usually causes rapid tyre wear.
- Suspension types include MacPherson strut and double wishbone; shock absorbers control spring oscillation, not load carrying alone.
Worked example
A car in first gear has a gearbox ratio of 3.5:1 and a final drive of 4.0:1. Overall reduction = 3.5 × 4.0 = 14:1. At 3,000 engine rpm, wheel speed = 3,000 ÷ 14 = about 214 rpm. Torque at the wheels is multiplied by roughly 14, less transmission losses. This explains why low gear gives strong acceleration but limited road speed.
Traps
Treating the differential as only a speed reducer; confusing camber with caster; setting toe without centring the steering; diagnosing a worn CV joint as a wheel bearing; assuming shock absorbers support vehicle weight.