Strut (MacPherson strut)
Definition
A MacPherson strut combines the shock absorber with a structural tube that locates the wheel: the coil spring sits around it, the bottom bolts to the knuckle and the top turns in a bearing inside the rubber strut mount, so the whole assembly steers with the wheel. Because it carries suspension loads as well as damping, the strut's piston rod, the top mount and its bearing and the spring seat all wear, in addition to normal damper leakage. Symptoms of a failed top mount or bearing are a clunk or creak when turning the wheel at low speed, a steering wheel that does not return to centre, a spring that can be heard winding up and releasing, and a knock over bumps; a leaking or weak strut gives nose dive, bounce, longer braking distances and cupped tyres. Compressing the spring is dangerous - use a proper compressor or buy a complete strut assembly - and the damper's position in the knuckle on some cars sets camber, so an alignment is required afterwards. No fault codes except on adaptive dampers (C-codes or manufacturer codes for the damper solenoid or ride height sensors, e.g. C1A3x, VAG 01772); related symptoms are noise, poor handling and uneven tyre wear.