Springs — Types and Purpose

Springs support the vehicle's weight at each corner and allow the suspension to travel through its designed range. Every time the wheel hits a bump and compresses the suspension, the spring stores that energy and releases it back as the wheel drops back down. The rate of the spring — how stiff it is — determines how much the vehicle reacts to road irregularities.

The most common spring type on modern passenger vehicles. A coil spring is a helix of spring steel wound around an axis. On MacPherson strut suspensions the spring wraps around the strut body. On double wishbone suspensions the spring often sits on the lower control arm. On some vehicles springs are separate from the shock and sit in their own perch.

A broken coil spring causes a sudden drop in ride height at the affected corner. The vehicle visibly sits lower on that corner. Sometimes a corner noise with every bump. Inspect all four spring seats — the rubber isolators at the top and bottom of the spring — whenever springs are being inspected. Deteriorated isolators allow spring noise and change ride height.

Used on light trucks and some SUVs. Multiple curved steel leaves stacked and clamped together. The longest leaf — the main leaf — curves up at both ends to form the spring eye where it mounts to the frame through the spring eye bushings and shackles. The other leaves are progressively shorter and add progressively more stiffness as the spring compresses under load.

Check leaf springs for broken individual leaves — a crack across any leaf changes spring rate significantly. Check the center bolt that clamps the leaves together — shearing of the center bolt allows the spring pack to shift and changes axle alignment. Check the spring eye bushings for cracking, tearing, or deterioration. Worn spring eye bushings are a very common cause of rear suspension noise and handling complaints on trucks.

Used on some trucks and SUVs as the front spring. A long steel bar runs front to rear. One end is anchored to the frame. The other end connects to the lower control arm. As the wheel moves up, the torsion bar twists. The resistance to twisting is what provides spring force. Ride height can be adjusted by moving the anchor point, which is why some trucks with torsion bar front suspension have a height adjustment bolt — turning it in or out changes the preload on the bar and changes front ride height.