MacPherson Strut — The Most Common Design

The MacPherson strut is the most common front suspension design in the world. Understanding how it works is fundamental because you will work on it more than any other suspension type. The genius of the design is that it combines several suspension functions into one compact assembly.

The MacPherson strut does three jobs simultaneously with one unit. It is the shock absorber — it controls the rate of wheel movement up and down. It is a structural member — the strut body connects the steering knuckle at the bottom to the strut tower in the engine compartment at the top. It serves as the upper pivot point for steering — on most MacPherson designs, the entire strut rotates when you turn the steering wheel.

Strut body — the large outer tube that mounts to the steering knuckle. Contains the shock absorber internals. Does not rotate when steering. Coil spring — sits on a spring perch that is part of the strut body. Supports the corner weight of the vehicle. Strut mount — at the very top of the assembly inside the strut tower. Contains a bearing that allows the strut to rotate when steering, and isolates the assembly from the body. This is a very common noise source — worn strut mounts click or thump when turning. The cartridge — the inner working component of the shock absorber inside the strut body. When a strut cartridge wears out, it no longer controls suspension movement properly.

A failed strut is not just a ride comfort problem. Because the strut is a load-bearing structural member, a failed strut changes the alignment geometry of that corner. Camber angle changes. Caster may change. Tire wear becomes uneven. On braking, the nose dives excessively and steering precision degrades. A vehicle with blown struts that 'drives fine' and 'brakes fine' is still eating tires unevenly and handling dangerously in emergency maneuvers. Always inspect strut condition as part of any tire wear diagnosis.