Steering and undercarriage — contact with the road

Steering and undercarriage are the systems that keep the car on the road and allow it to be steered precisely and drive stably. When something wears or gets play, it is felt as imprecise steering, poor grip or uneven tyre wear — and it affects both comfort and safety. As a mechanic, you must be able to assess these systems both while driving and during control on a lift.

§The suspension's task

The suspension connects the wheels to the body so the wheels can follow the road's irregularities without shaking the entire car. It typically consists of control arms, bushings, springs and shock absorbers plus joints that allow the wheel to move up and down and simultaneously turn. The geometry of the suspension determines how the wheels are positioned relative to the road — and thus how well the car steers and brakes.

§Springs and shock absorbers

Springs carry the car's weight and absorb the shocks from the road while shock absorbers slow the springs' movement so the car doesn't continue to rock. A worn shock absorber shows up in the car bouncing or tilting after a bump and it lengthens braking distance because the wheel loses contact with the road. Spring and shock absorber always work together — if one is defective the handling suffers.

§The steering from wheel to wheels

When the driver turns the wheel, the movement is transferred through the steering box or rack and pinion and further out to the tie rods and steering arms to the wheels. Most cars have power steering, where hydraulics or an electric motor amplifies the driver's force. Play in tie rods or a leaky power steering gives imprecise steering, and it must be found and corrected because steering is safety-critical.

Signs of wear in steering and suspension

• 01Clicking sounds over bumps — worn bushings, joints or load-bearing arms.
• 02The car sways or rocks after a bump — worn shock absorbers.
• 03Imprecise or loose steering—slack in steering linkage or steering box.
• 04The vehicle pulls to the side or has a crooked steering wheel — wheel alignment out of adjustment.
• 05Uneven or one-sided tire wear—error in wheel alignment or worn suspension.

§Inspection with care

Many wear faults are found easiest with wheels unloaded on a lift where you can shake the wheels and feel for play in certain directions. Combine it with a test drive where you listen and feel how the car behaves. Always cross-check your findings with the manufacturer's wear limits and remember that a suspension fault rarely comes alone — check both sides so you do not deliver a car that pulls to one side.