Suspension, Steering & Tires
MacPherson struts, control arms, sway bars, power steering, wheel alignment, tire service, TPMS, and wheel bearing diagnosis.
- Identify common front and rear suspension components and their functions
- Explain power steering system operation and common failures
- Define wheel alignment angles and their effects on tire wear
- Describe tire service procedures including TPMS, rotation, and balancing
- Diagnose wheel bearing noise and suspension wear
Leçon 1
Suspension Types, Struts, Control Arms & Sway Bars
Purpose of the Suspension System
The suspension system serves two primary purposes: it maintains tire contact with the road and it absorbs road shocks to provide a comfortable ride. Without a properly functioning suspension, the vehicle would bounce uncontrollably, lose traction, and become dangerous to drive.
MacPherson Strut Suspension
The MacPherson strut is the most widely used front suspension design. It combines the shock absorber and upper steering pivot into a single unit, reducing weight and complexity.
Components of a MacPherson strut assembly:
- Strut housing - contains the shock absorber (damper) and serves as the upper steering knuckle pivot
- Coil spring - supports the vehicle weight and absorbs major bumps
- Upper strut mount - bolts to the strut tower and includes a bearing for steering rotation
- Lower control arm - connects the steering knuckle to the frame and controls wheel position
- Ball joint - the pivot between the lower control arm and the steering knuckle
Spring Compressor Safety
A coil spring under compression stores enormous energy. Always use a proper spring compressor tool when disassembling a strut. A spring that releases uncontrolled can cause serious injury or death.
Double Wishbone (SLA) Suspension
The double wishbone (also called short-long arm or SLA) suspension uses an upper control arm and a lower control arm connected to the knuckle by ball joints. This design provides better camber control during suspension travel, making it popular on performance and luxury vehicles.
Rear Suspension Types
- Multi-link - uses multiple arms for precise wheel control; common on modern vehicles
- Torsion beam (twist beam) - a solid beam connecting rear wheels; simple and cost-effective for front-wheel-drive vehicles
- Leaf springs - used on trucks and heavy-duty vehicles for load-carrying capacity
Sway Bar (Stabilizer Bar)
The sway bar (stabilizer bar) connects the left and right suspension through sway bar links and bushings. Its purpose is to reduce body roll during cornering by transferring force from the compressed side to the unloaded side. Worn sway bar links produce a clunking noise over bumps.
The MacPherson strut is the most common front suspension design, combining the shock absorber and upper steering pivot in one unit. The sway bar reduces body roll during cornering. Always use a spring compressor when servicing strut assemblies.